0000066756-24-000007 | 10-K | XBRL Viewer

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Commitments, Guarantees and Contingencies - Capacity and Energy Table (Details) - MW	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Manitoba Hydro \| Minnesota Power \| Manitoba Hydro PPA (Expires 2040)
Power Purchase Agreements [Line Items]
Output being purchased - electric energy (MW)	133
Manitoba Hydro \| Minnesota Power \| Manitoba Hydro PPA (Expires May 2035)
Power Purchase Agreements [Line Items]
Output being purchased - electric energy and capacity (MW)	250
Tenaska \| Minnesota Power \| Nobles 2
Power Purchase Agreements [Line Items]
Output being purchased - electric energy and capacity (MW)	250
Oliver Wind \| Minnesota Power \| Oliver Wind I PPA
Power Purchase Agreements [Line Items]
Output being purchased - electric energy (MW)	50
Oliver Wind \| Minnesota Power \| Oliver Wind II PPA
Power Purchase Agreements [Line Items]
Output being purchased - electric energy (MW)	48
Basin \| Minnesota Power \| Basin Power Sales Agreement (Expires May 2028)
Power Purchase Agreements [Line Items]
Output being sold electric - capacity (MW)	100
Great River Energy \| Minnesota Power \| Great River Energy Power Sales Agreement (Expires May 2025)
Power Purchase Agreements [Line Items]
Output being sold electric - capacity (MW)	100
Oconto Electric Cooperative \| Minnesota Power \| Oconto Electric Cooperative Power Sales Agreement
Power Purchase Agreements [Line Items]
Output being sold electric - energy and capacity (MW)	25
Basin Electric Power Cooperative \| Minnesota Power \| Basin Electric Cooperative PSA June 2022 - May 2023
Power Purchase Agreements [Line Items]
Output being sold electric - capacity (MW)	75
Basin Electric Power Cooperative \| Minnesota Power \| Basin Electric Cooperative PSA June 2023 - May 2025
Power Purchase Agreements [Line Items]
Output being sold electric - capacity (MW)	125
Square Butte \| Minnesota Power \| Square Butte PPA \| Square Butte Coal-fired Unit
Power Purchase Agreements [Line Items]
Expected output entitlement	50.00%
Minnkota Power \| Square Butte PPA \| Minnkota Sales Agreement \| Square Butte Coal-fired Unit
Power Purchase Agreements [Line Items]
Expected output entitlement	37.00%	32.00%	28.00%
Silver Bay Power \| Minnesota Power \| Silver Bay Power Self-Generation
Power Purchase Agreements [Line Items]
Energy generation owned (MW)	90
Calpine Corporation PPA \| Calpine Corporation \| Minnesota Power
Power Purchase Agreements [Line Items]
Output being purchased - electric capacity (MW)	25

Operations and Significant Accounting Policies - Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Lessee, Lease, Description [Line Items]
Operating Lease Cost	$ 5.0	$ 6.3
Finance Lease Cost	0.1	0.0
Operating Cash Flows From Operating Leases	5.0	6.3
Financing Cash Flows From Finance Leases	$ 0.2	$ 0.0
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other Non-Current Assets	Other Non-Current Assets
Operating Lease Other Non-Current Assets	$ 10.7	$ 12.7
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other Non-Current Assets	Other Non-Current Assets
Finance Lease Other Non-Current Assets	$ 2.1	$ 0.0
Total Lease Right-of-use Assets	$ 12.8	$ 12.7
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other	Other
Operating Lease Liabilities	$ 3.0	$ 3.2
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other	Other
Finance Lease Liabilities	$ 0.4	$ 0.0
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other Non-Current Liabilities	Other Non-Current Liabilities
Operating Lease Liabilities	$ 7.7	$ 9.3
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other Non-Current Liabilities	Other Non-Current Liabilities
Finance Lease Liabilities	$ 1.6	$ 0.0
Total Lease Liabilities	12.7	12.5
Finance Lease Amortization Expense	0.1	0.0
Total Operating and Finance Lease Expenses	$ 5.1	$ 6.3
Vehicles and Equipment
Weighted Average Remaining Lease Term (Years):
Operating Leases	3 years	4 years
Finance Leases	5 years	0 years
Weighted Average Discount Rate:
Operating Lease	4.00%	3.90%
Finance Lease	5.40%	0.00%
Land and Other
Weighted Average Remaining Lease Term (Years):
Operating Leases	12 years	16 years
Weighted Average Discount Rate:
Operating Lease	5.00%	3.90%

Property, Plant and Equipment

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

PROPERTY, PLANT AND EQUIPMENT


Property, Plant and Equipment
As of December 31	2023	2022
Millions
Regulated Operations
Property, Plant and Equipment in Service	$5,167.2	$5,198.6

Construction Work in Progress	146.7	74.0
Accumulated Depreciation	(1,969.4)	(1,972.3)
Regulated Operations – Net	3,344.5	3,300.3
ALLETE Clean Energy
Property, Plant and Equipment in Service	1,612.8	1,619.4
Construction Work in Progress	48.9	51.1
Accumulated Depreciation	(229.1)	(176.8)
ALLETE Clean Energy – Net	1,432.6	1,493.7






Corporate and Other (a)
Property, Plant and Equipment in Service	355.8	295.2
Construction Work in Progress	27.5	50.9
Accumulated Depreciation	(147.0)	(136.1)
Corporate and Other – Net	236.3	210.0
Property, Plant and Equipment – Net	$5,013.4	$5,004.0

(a)Primarily includes BNI Energy and a small amount of non-rate base generation.

NOTE 2. PROPERTY, PLANT AND EQUIPMENT (Continued)

Depreciation is computed using the straight-line method over the estimated useful lives of the various classes of assets.

Estimated Useful Lives of Property, Plant and Equipment (Years)

Regulated Operations

Generation

4 to 50

ALLETE Clean Energy

5 to 35

Transmission

50 to 75

Corporate and Other

3 to 50

Distribution

18 to 70

Asset Retirement Obligations. We recognize, at fair value, obligations associated with the retirement of certain tangible, long lived assets that result from the acquisition, construction, development or normal operation of the asset. Asset retirement obligations (AROs) relate primarily to the decommissioning of our coal-fired and wind energy facilities, and land reclamation at BNI Energy. AROs are included in Other Non-Current Liabilities on the Consolidated Balance Sheet. The associated retirement costs are capitalized as part of the related long-lived asset and depreciated over the useful life of the asset. Removal costs associated with certain distribution and transmission assets have not been recognized, as these facilities have indeterminate useful lives.

Conditional asset retirement obligations have been identified for treated wood poles and remaining polychlorinated biphenyl and asbestos-containing assets; however, the period of remediation is indeterminable and removal liabilities have not been recognized.

Long-standing ratemaking practices approved by applicable state and federal regulatory authorities have allowed provisions for future plant removal costs in depreciation rates. These plant removal cost recoveries are classified either as AROs or as a regulatory liability for non-AROs. To the extent annual accruals for plant removal costs differ from accruals under approved depreciation rates, a regulatory asset has been established in accordance with GAAP for AROs. (See Note 4. Regulatory Matters.)


Asset Retirement Obligations
Millions
Obligation as of December 31, 2021						$184.5
Accretion						9.5
Liabilities Recognized						7.8
Liabilities Settled						(4.4)
Revisions in Estimated Cash Flows						3.0
Obligation as of December 31, 2022						200.4
Accretion						10.3

Liabilities Settled						(10.2)
Revisions in Estimated Cash Flows						2.4
Obligation as of December 31, 2023						$202.9

Operations and Significant Accounting Policies - Inventories (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Fuel	$ 27.2	$ 33.4
Materials and Supplies	115.7	75.1
Renewable Energy Energy Facilities Under Development	32.5	347.4
Total Inventories – Net	$ 175.4	$ 455.9

Employee Stock and Incentive Plans - Narrative (Details) - USD ($)	1 Months Ended		12 Months Ended
	Feb. 29, 2024	Jan. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Stock-based Compensation [Line Items]
ESOP compensation expense			$ 13,700,000	$ 12,000,000	$ 11,500,000
Capitalized share-based compensation costs			$ 0	$ 0	$ 0
Executive Long-Term Incentive Compensation Plan
Stock-based Compensation [Line Items]
Common stock reserved (in shares)			700,000
Shares available for issuance (in shares)			600,000
Employee Stock Purchase Plan (ESPP)
Stock-based Compensation [Line Items]
ESPP discount			5.00%
Performance Shares
Stock-based Compensation [Line Items]
Unrecognized compensation cost			$ 2,600,000
Weighted-average period for recognition			1 year 8 months 12 days
Granted (in shares)			54,039	37,731	33,304
Awarded (in shares)			0	0	0
Vesting period			3 years
Performance Shares \| Subsequent Event
Stock-based Compensation [Line Items]
Granted (in shares)		61,900
Granted, grant date fair value		$ 4,000,000
Awarded (in shares)	46,700
Awarded, grant date fair value	$ 3,300,000
Vesting period		3 years
Restricted Stock Units
Stock-based Compensation [Line Items]
Unrecognized compensation cost			$ 800,000
Weighted-average period for recognition			1 year 8 months 12 days
Granted (in shares)			21,200	15,477	16,251
Awarded (in shares)			9,631	7,396	23,631
Vesting period			3 years
Restricted Stock Units \| Subsequent Event
Stock-based Compensation [Line Items]
Granted (in shares)		24,300
Granted, grant date fair value		$ 1,400,000
Awarded (in shares)	11,200
Awarded, grant date fair value	$ 700,000

Pension and Other Postretirement Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net Loss	$ 2.5	$ 11.4
Amortization of Prior Service Credit	0.1	0.1
Prior Service Credit Arising During the Period	0.0	0.8
Amortization of Gain (Loss)	(5.7)	(11.4)
Amortization of Prior Service Credit	(0.1)	(0.1)
Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities	(3.1)	0.9
Postretirement Health and Life Obligation and Funded Status
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net Loss	(18.3)	3.9
Prior Service Credit Arising During the Period	(29.1)	0.0
Amortization of Prior Service Credit	8.4	7.5
Amortization of Gain (Loss)	2.7	(0.4)
Amortization of Prior Service Credit	(8.4)	(7.5)
Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities	$ (36.3)	$ 11.0

Operations and Significant Accounting Policies - Other Current Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Customer Deposits	$ 7.4	$ 150.7
PSAs	6.0	6.1
Provision for Interim Rate Refund	0.0	18.4
Manufactured Gas Plant	0.8	14.7
Other	77.7	61.1
Total Other Current Liabilities	$ 91.9	$ 251.0

Income Tax Expense - Gross Unrecognized Income Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Gross Unrecognized Income Tax Benefits [Roll Forward]
Balance at January 1	$ 1.3	$ 1.3	$ 1.4
Reductions for Tax Positions Related to Prior Years	(0.2)	0.0	(0.1)
Balance as of December 31	$ 1.1	$ 1.3	$ 1.3

Pension and Other Postretirement Benefit Plans - Estimated Future Benefit Payments (Details) $ in Millions	Dec. 31, 2023 USD ($)
Pension
Estimated Future Benefit Payments [Abstract]
2024	$ 58.4
2025	58.1
2026	57.5
2027	57.2
2028	56.9
Years 2029 – 2033	272.6
Postretirement Health and Life
Estimated Future Benefit Payments [Abstract]
2024	6.3
2025	6.2
2026	6.1
2027	6.1
2028	6.0
Years 2029 – 2033	$ 30.0

Short-Term and Long-Term Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Long-term debt	$ 1,799.4	$ 1,929.1
Unamortized Debt Issuance Costs	(8.1)	(8.3)
Total Long-Term Debt	1,791.3	1,920.8
Less: Due Within One Year	111.4	272.6
Net Long-Term Debt	$ 1,679.9	1,648.2
6.02% Series Due 2023
Debt Instrument [Line Items]
Interest rate	6.02%
Long-term debt	$ 0.0	75.0
3.69% Series Due 2024
Debt Instrument [Line Items]
Interest rate	3.69%
Long-term debt	$ 60.0	60.0
4.90% Series Due 2025
Debt Instrument [Line Items]
Interest rate	4.90%
Long-term debt	$ 30.0	30.0
5.10% Series Due 2025
Debt Instrument [Line Items]
Interest rate	5.10%
Long-term debt	$ 30.0	30.0
3.20% Series Due 2026
Debt Instrument [Line Items]
Interest rate	3.20%
Long-term debt	$ 75.0	75.0
5.99% Series Due 2027
Debt Instrument [Line Items]
Interest rate	5.99%
Long-term debt	$ 60.0	60.0
3.30% Series Due 2028
Debt Instrument [Line Items]
Interest rate	3.30%
Long-term debt	$ 40.0	40.0
4.08% Series Due 2029
Debt Instrument [Line Items]
Interest rate	4.08%
Long-term debt	$ 70.0	70.0
3.74% Series Due 2029
Debt Instrument [Line Items]
Interest rate	3.74%
Long-term debt	$ 50.0	50.0
2.50% Series Due 2030
Debt Instrument [Line Items]
Interest rate	2.50%
Long-term debt	$ 46.0	46.0
3.86% Series Due 2030
Debt Instrument [Line Items]
Interest rate	3.86%
Long-term debt	$ 60.0	60.0
2.79% Series Due 2031
Debt Instrument [Line Items]
Interest rate	2.79%
Long-term debt	$ 100.0	100.0
4.54% Series Due 2032
Debt Instrument [Line Items]
Interest rate	4.54%
Long-term debt	$ 75.0	75.0
4.98% Series Due 2033
Debt Instrument [Line Items]
Interest rate	4.98%
Long-term debt	$ 125.0	0.0
5.69% Series Due 2036
Debt Instrument [Line Items]
Interest rate	5.69%
Long-term debt	$ 50.0	50.0
6.00% Series Due 2040
Debt Instrument [Line Items]
Interest rate	6.00%
Long-term debt	$ 35.0	35.0
5.82% Series Due 2040
Debt Instrument [Line Items]
Interest rate	5.82%
Long-term debt	$ 45.0	45.0
4.08% Series Due 2042
Debt Instrument [Line Items]
Interest rate	4.08%
Long-term debt	$ 85.0	85.0
4.21% Series Due 2043
Debt Instrument [Line Items]
Interest rate	4.21%
Long-term debt	$ 60.0	60.0
4.95% Series Due 2044
Debt Instrument [Line Items]
Interest rate	4.95%
Long-term debt	$ 40.0	40.0
5.05% Series Due 2044
Debt Instrument [Line Items]
Interest rate	5.05%
Long-term debt	$ 40.0	40.0
4.39% Series Due 2044
Debt Instrument [Line Items]
Interest rate	4.39%
Long-term debt	$ 50.0	50.0
4.07% Series Due 2048
Debt Instrument [Line Items]
Interest rate	4.07%
Long-term debt	$ 60.0	60.0
4.47% Series Due 2049
Debt Instrument [Line Items]
Interest rate	4.47%
Long-term debt	$ 30.0	30.0
3.30% Series Due 2050
Debt Instrument [Line Items]
Interest rate	3.30%
Long-term debt	$ 94.0	94.0
Armenia Mountain Senior Secured Notes 3.26% Due 2024
Debt Instrument [Line Items]
Interest rate	3.26%
Long-term debt	$ 9.5	19.3
Industrial Development Variable Rate Demand Refunding Revenue Bonds Series 2006, Due 2025
Debt Instrument [Line Items]
Long-term debt	27.8	27.8
Revolving Credit Facility Variable Rate Due 2027
Debt Instrument [Line Items]
Long-term debt	$ 0.0	13.0
Senior Unsecured Notes 2.65% Due 2025
Debt Instrument [Line Items]
Interest rate	2.65%
Long-term debt	$ 150.0	150.0
Senior Unsecured Notes 3.11% Due 2027
Debt Instrument [Line Items]
Interest rate	3.11%
Long-term debt	$ 80.0	80.0
SWL&P First Mortgage Bonds 4.15% Series Due 2028
Debt Instrument [Line Items]
Interest rate	4.15%
Long-term debt	$ 15.0	15.0
SWL&P First Mortgage Bonds 4.14% Series Due 2048
Debt Instrument [Line Items]
Interest rate	4.14%
Long-term debt	$ 12.0	12.0
Unsecured Term Loan Variable Rate Due 2023
Debt Instrument [Line Items]
Long-term debt	$ 0.0	170.0
Other Long-Term Debt, 2023 Weighted Average Rate 5.24% Due 2024 – 2051
Debt Instrument [Line Items]
Interest rate	5.24%
Long-term debt	$ 95.1	$ 82.0

Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2023

Selected Quarterly Financial Information [Abstract]

Quarterly Financial Data (Unaudited)

QUARTERLY FINANCIAL DATA (UNAUDITED)

Information for any one quarterly period is not necessarily indicative of the results which may be expected for the year.


Quarter Ended	Mar. 31	Jun. 30	Sept. 30	Dec. 31
Millions Except Earnings Per Share
2023
Operating Revenue	$564.9	$533.4	$378.8	$402.7
Operating Income	$48.3	$53.5	$36.0	$43.1
Net Income Attributable to ALLETE	$58.2	$51.5	$85.9	$51.5
Earnings Per Share of Common Stock
Basic	$1.02	$0.90	$1.50	$0.89
Diluted	$1.02	$0.90	$1.49	$0.89
2022
Operating Revenue	$383.5	$373.1	$388.3	$425.8
Operating Income	$53.4	$13.7	$33.4	$33.7
Net Income Attributable to ALLETE	$66.3	$37.6	$33.7	$51.7
Earnings Per Share of Common Stock
Basic	$1.24	$0.67	$0.59	$0.90
Diluted	$1.24	$0.67	$0.59	$0.90
2021
Operating Revenue	$339.2	$335.6	$345.4	$399.0
Operating Income	$42.0	$28.2	$31.1	$50.0
Net Income Attributable to ALLETE	$51.8	$27.9	$27.6	$61.9
Earnings Per Share of Common Stock
Basic	$0.99	$0.53	$0.53	$1.18
Diluted	$0.99	$0.53	$0.53	$1.18

Regulatory Matters - Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Assets	$ 9.3	$ 25.6
Total Non-Current Regulatory Assets	425.4	441.0
Total Current Regulatory Liabilities	3.9	23.4
Total Non-Current Regulatory Liabilities	574.0	526.1
Provision for Interim Rate Refund
Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Liabilities	0.0	18.4
Transmission Formula Rates Refund
Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Liabilities	1.5	4.9
Other
Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Liabilities	2.4	0.1
Total Non-Current Regulatory Liabilities	4.4	4.2
Income Taxes
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	310.0	332.5
Wholesale and Retail Contra AFUDC
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	78.0	80.7
Plant Removal Obligations
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	67.0	60.0
Defined Benefit Pension and Other Postretirement Benefit Plans
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	48.6	17.6
Non-Jurisdictional Land Sales
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	30.2	7.5
Fuel Adjustment Clause
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	15.5	0.0
Investment Tax Credits
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	13.6	16.9
Boswell Units 1 and 2 Net Plant and Equipment
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	6.7	6.7
Fuel Adjustment Clause
Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Assets	8.7	25.6
Total Non-Current Regulatory Assets	5.0	14.5
Other
Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Assets	0.6	0.0
Total Non-Current Regulatory Assets	4.2	7.0
Defined Benefit Pension and Other Postretirement Benefit Plans
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	218.6	225.9
Income Taxes
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	88.1	97.6
Asset Retirement Obligations
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	37.7	35.6
Cost Recovery Riders
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	33.8	41.2
Taconite Harbor
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	20.9	0.0
Manufactured Gas Plant
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	13.2	15.1
PPACA Income Tax Deferral
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	$ 3.9	$ 4.1

Short-Term and Long-Term Debt - Narrative (Details) $ in Millions		12 Months Ended
	Apr. 27, 2023 USD ($)	Dec. 31, 2023 USD ($)	Oct. 17, 2023 USD ($)	Oct. 16, 2023 USD ($)	Dec. 31, 2022 USD ($)
Debt Instrument [Line Items]
Short-term debt - outstanding		$ 111.4			$ 272.6
Short-term debt - unamortized debt issuance costs		0.1
Long-Term Debt		1,679.9			1,648.2
Long-term debt - unamortized debt issuance costs		8.0
Long-term debt maturing in 2024		111.4
Long-term debt maturing in 2025		244.7
Long-term debt maturing in 2026		80.2
Long-term debt maturing in 2027		162.5
Long-term debt maturing in 2028		55.8
Long-term debt maturing thereafter		$ 1,144.8
Actual indebtedness to total capitalization ratio		0.36
Maximum
Debt Instrument [Line Items]
Allowed indebtedness to total capitalization ratio		0.65
Bank Lines of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 423.1			475.7
Standby letters of credit		19.4			32.8
Draws outstanding		34.1			$ 31.3
Credit Agreement \| Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 355.0	$ 400.0
Extension period			1 year
Issuable letters of credit			$ 100.0
Camp Ripley Financing
Debt Instrument [Line Items]
Annual financing payment		$ 1.4
Financing renewal term		2 years
Purchase option		$ 4.0
ALLETE Bonds 4.98% Due April 2033
Debt Instrument [Line Items]
Proceeds from issuance of First Mortgage Bond	$ 125.0
Interest rate	4.98%

Pension and Other Postretirement Benefit Plans - Reconciliation of Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet (Details) - Postretirement Health and Life - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net Gain	$ (24.8)	$ (9.2)
Prior Service Credit	33.8	13.2
Accumulated Net Periodic Benefit Cost in Excess of Contributions	41.3	29.8
Total Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet	$ 99.9	$ 52.2

Operations and Significant Accounting Policies - Other Income (Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other	$ 85.0	$ 22.4	$ 8.7
Pension and Other Postretirement Benefit Plan Non-Service Credit
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other	8.9	9.8	6.1
Interest and Investment Income
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other	10.3	0.0	2.3
AFUDC - Equity
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other	3.6	2.7	2.6
Gain on Land Sales
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other	0.2	0.0	0.1
PSA Liability
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other	0.0	10.2	0.0
Gain on Arbitration Award
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other	58.4	0.0	0.0
Other
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other	3.6	$ (0.3)	$ (2.4)
Interest Income Related To Interest Awarded As Part Of An Arbitration Ruling
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other	$ 5.1

Audit Information	12 Months Ended
Audit Information	Dec. 31, 2023
Auditor Information [Abstract]
Auditor Name	PricewaterhouseCoopers LLP
Auditor Firm ID	238
Auditor Location	Minneapolis, MN

Acquisitions - Schedule of Recognized Identified Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Apr. 15, 2022	Dec. 31, 2021	Dec. 31, 2020
Business Acquisition [Line Items]
Cash and Cash Equivalents	$ 79.4	$ 40.2		$ 47.7	$ 65.2
Goodwill	$ 154.9
New Energy
Business Acquisition [Line Items]
Cash and Cash Equivalents			$ 3.9
Accounts Receivable			1.4
Inventory			25.3
Other Current Assets			12.8
Property, Plant and Equipment - Net			16.4
Goodwill			154.9
Other Non-Current Assets			2.1
Total Assets Acquired			216.8
Current Liabilities			23.6
Long-Term Debt Due Within One Year			28.3
Long-Term Debt			5.9
Other Non-Current Liabilities			0.2
Total Liabilities Assumed			58.0
Net Identifiable Assets Acquired			158.8
Fair value adjustments			11.6
Deductible goodwill			$ 154.9

Pension and Other Postretirement Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

Obligation and Funded Status


Pension Obligation and Funded Status
As of December 31	2023	2022
Millions
Accumulated Benefit Obligation	$729.5	$724.5
Change in Benefit Obligation
Obligation, Beginning of Year	$739.7	$911.7
Service Cost	6.5	9.3
Interest Cost	40.5	27.2
Plan Amendments	—	0.8

Actuarial (Gain) Loss (a)	13.9	(160.6)
Benefits Paid	(60.9)	(58.9)
Participant Contributions	6.6	10.2
Obligation, End of Year	$746.3	$739.7
Change in Plan Assets
Fair Value, Beginning of Year	$568.6	$745.7
Actual Return on Plan Assets	55.1	(130.5)
Employer Contribution (b)	26.2	12.3
Benefits Paid	(60.9)	(58.9)
Fair Value, End of Year	$589.0	$568.6
Funded Status, End of Year	$(157.3)	$(171.1)

Net Pension Amounts Recognized in Consolidated Balance Sheet Consist of:
Current Liabilities	$(2.1)	$(2.1)
Non-Current Liabilities	$(155.2)	$(169.0)

(a) Actuarial gain in 2022 was primarily the result of increases in discount rates.

(b) Includes Participant Contributions noted above, any contributions made by the Company to pension plan trusts and any direct benefit payments made under certain plans.


Postretirement Health and Life Obligation and Funded Status
As of December 31	2023	2022
Millions
Change in Benefit Obligation
Obligation, Beginning of Year	$110.4	$148.2
Service Cost	2.0	3.0
Interest Cost	5.6	4.4
Actuarial Gain (a)	(9.3)	(38.7)
Benefits Paid	(8.1)	(9.2)
Participant Contributions	2.4	2.7
Plan Amendments (b)	(29.1)	—


Obligation, End of Year	$73.9	$110.4
Change in Plan Assets
Fair Value, Beginning of Year	$162.6	$201.8
Actual Return on Plan Assets	20.3	(33.0)
Employer Contribution (Withdrawal)	(3.4)	0.3
Participant Contributions	2.4	2.7
Benefits Paid	(8.1)	(9.2)
Fair Value, End of Year	$173.8	$162.6
Funded Status, End of Year	$99.9	$52.2

Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet Consist of:
Non-Current Assets	$106.3	$58.8
Current Liabilities	$(0.2)	$(0.2)
Non-Current Liabilities	$(6.2)	$(6.4)

(a)Actuarial gain in 2022 was primarily the result of increases in discount rates.

(b)In 2023, the postretirement health care plan was amended to change the company contribution to an annual stipend for certain retirees.

Amounts Recognized in Consolidated Balance Sheet


Reconciliation of Net Pension Amounts Recognized in Consolidated Balance Sheet
As of December 31	2023	2022
Millions
Net Loss	$(256.9)	$(260.2)
Prior Service Credit	—	0.1
Accumulated Contributions in Excess of Net Periodic Benefit Cost (Prepaid Pension Asset)	99.6	89.0
Total Net Pension Amounts Recognized in Consolidated Balance Sheet	$(157.3)	$(171.1)


Reconciliation of Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet
As of December 31	2023	2022
Millions
Net Gain (a)	$24.8	$9.2
Prior Service Credit	33.8	13.2
Accumulated Net Periodic Benefit Cost in Excess of Contributions (a)	41.3	29.8
Total Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet	$99.9	$52.2

(a)Excludes gains, losses and contributions associated with irrevocable grantor trusts.

Components of Net Periodic Cost


Components of Net Periodic Pension Cost
Year Ended December 31	2023	2022	2021
Millions
Service Cost	$6.5	$9.3	$11.0
Non-Service Cost Components (a)
Interest Cost	40.5	27.2	24.6
Expected Return on Plan Assets	(43.8)	(41.5)	(43.4)
Amortization of Loss	5.8	11.4	18.8
Amortization of Prior Service Credit	(0.1)	(0.1)	(0.2)
Net Pension Cost	$8.9	$6.3	$10.8

(a)These components of net periodic pension cost are included in the line item “Other” under Other Income (Expense) on the Consolidated Statement of Income.


Components of Net Periodic Postretirement Health and Life Cost
Year Ended December 31	2023	2022	2021
Millions
Service Cost	$2.0	$3.0	$3.6
Non-Service Cost Components (a)
Interest Cost	5.6	4.4	4.4
Expected Return on Plan Assets	(11.4)	(9.6)	(9.9)
Amortization of (Gain) Loss	(2.7)	0.4	3.0
Amortization of Prior Service Credit	(8.5)	(7.5)	(7.6)


Net Postretirement Health and Life Credit	$(15.0)	$(9.3)	$(6.5)

(a)These components of net periodic postretirement health and life cost are included in the line item “Other” under Other Income (Expense) on the Consolidated Statement of Income.

Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities


Other Changes in Pension Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities
Year Ended December 31	2023	2022
Millions
Net Loss	$2.5	$11.4
Amortization of Prior Service Credit	0.1	0.1
Prior Service Credit Arising During the Period	—	0.8
Amortization of Loss	(5.7)	(11.4)
Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities	$(3.1)	$0.9


Other Changes in Postretirement Benefit Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities
Year Ended December 31	2023	2022
Millions
Net (Gain) Loss	$(18.3)	$3.9
Prior Service Credit Arising During the Period	(29.1)	—
Amortization of Prior Service Credit	8.4	7.5

Amortization of Gain (Loss)	2.7	(0.4)

Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities	$(36.3)	$11.0

Information for Pension Plans with an Accumulated Benefit Obligation in Excess of Plan Assets


Information for Pension Plans with an Accumulated Benefit Obligation in Excess of Plan Assets
As of December 31	2023	2022
Millions
Projected Benefit Obligation	$746.3	$739.7
Accumulated Benefit Obligation	$729.5	$724.5
Fair Value of Plan Assets	$589.0	$568.6

Unrecognized Postretirement Health and Life Costs

The postretirement health and life costs that are reported as a component within the Consolidated Balance Sheet, reflected in regulatory long-term assets or liabilities and accumulated other comprehensive income, consist of the following:


Unrecognized Postretirement Health and Life Costs
As of December 31	2023	2022
Millions
Net Gain	$(24.8)	$(9.2)
Prior Service Credit	(33.8)	(13.2)

Total Unrecognized Postretirement Health and Life Cost	$(58.6)	$(22.4)

Estimated Future Benefit Payments


Estimated Future Benefit Payments	Pension	Postretirement Health and Life
Millions
2024	$58.4	$6.3
2025	$58.1	$6.2
2026	$57.5	$6.1
2027	$57.2	$6.1
2028	$56.9	$6.0
Years 2029 – 2033	$272.6	$30.0

Weighted Average Assumptions Used to Determine Benefit Obligation and Net Periodic Benefit Costs


Weighted Average Assumptions Used to Determine Benefit Obligation
As of December 31	2023	2022
Discount Rate
Pension	5.39%	5.70%
Postretirement Health and Life	5.42%	5.68%
Rate of Compensation Increase	3.52%	3.58%
Health Care Trend Rates
Trend Rate	7.00%	6.50%
Ultimate Trend Rate	5.00%	5.00%
Year Ultimate Trend Rate Effective	2038	2038


Weighted Average Assumptions Used to Determine Net Periodic Benefit Costs
Year Ended December 31	2023	2022	2021
Discount Rate
Pension	5.70%	3.28%	2.87%
Postretirement Health and Life	5.89%	3.09%	2.70%
Expected Long-Term Return on Plan Assets
Pension	6.83%	6.00%	6.50%
Postretirement Health and Life	6.33%	5.41%	5.85%
Rate of Compensation Increase	3.58%	3.58%	3.62%

Plan Asset Actual and Target Allocations


Actual Plan Asset Allocations	Pension		Postretirement Health and Life (a)
	2023	2022	2023	2022
Equity Securities	57%	46%	67%	66%
Fixed Income Securities	40%	50%	33%	34%

Real Estate	3%	4%	—	—
	100%	100%	100%	100%

(a)Includes VEBAs and irrevocable grantor trusts.

Following are the current targeted allocations as of December 31, 2023:


Plan Asset Target Allocations	Pension		Postretirement Health and Life (a)
Equity Securities	55	%	65	%
Fixed Income Securities	41	%	35	%

Real Estate	4	%	—
	100	%	100	%

(a)Includes VEBAs and irrevocable grantor trusts.

Recurring Fair Value Measures


	Fair Value as of December 31, 2023
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets:
Equity Securities:
U.S. Large-cap (a)	—	$83.7	—	$83.7
U.S. Mid-cap Growth (a)	—	69.9	—	69.9
U.S. Small-cap (a)	—	46.5	—	46.5

International	$134.6	—	—	134.6



Fixed Income Securities (a)	—	215.0	—	215.0
Cash and Cash Equivalents	20.4	—	—	20.4


Real Estate	—	—	$18.9	18.9
Total Fair Value of Assets	$155.0	$415.1	$18.9	$589.0

(a)The underlying investments consist of actively-managed funds managed to achieve the returns of certain U.S. equity and fixed income securities indexes.


	Fair Value as of December 31, 2022
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets:
Equity Securities:
U.S. Large-cap (a)	—	$61.2	—	$61.2
U.S. Mid-cap Growth (a)	—	40.0	—	40.0
U.S. Small-cap (a)	—	35.4	—	35.4

International	$127.0	—	—	127.0



Fixed Income Securities (a)	—	275.3	—	275.3
Cash and Cash Equivalents	7.3	—	—	7.3


Real Estate	—	—	$22.4	22.4
Total Fair Value of Assets	$134.3	$411.9	$22.4	$568.6

(a)The underlying investments consist of actively-managed funds managed to achieve the returns of certain U.S. equity and fixed income securities indexes.


	Fair Value as of December 31, 2023
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets:
Equity Securities: (a)
U.S. Large-cap	$30.0	—	—	$30.0
U.S. Mid-cap Growth	28.7	—	—	28.7
U.S. Small-cap	14.9	—	—	14.9
International	41.9	—	—	41.9
Fixed Income Securities:
Mutual Funds	55.1	—	—	55.1

Cash and Cash Equivalents	3.2	—	—	3.2


Total Fair Value of Assets	$173.8	—	—	$173.8

(a)The underlying investments consist of mutual funds (Level 1).


	Fair Value as of December 31, 2022
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets:
Equity Securities: (a)
U.S. Large-cap	$26.7	—	—	$26.7
U.S. Mid-cap Growth	25.5	—	—	25.5
U.S. Small-cap	12.7	—	—	12.7
International	41.5	—	—	41.5
Fixed Income Securities:
Mutual Funds	55.5	—	—	55.5
Cash and Cash Equivalents	0.7	—	—	0.7

Total Fair Value of Assets	$162.6	—	—	$162.6

(a)The underlying investments consist of mutual funds (Level 1).

NOTE 12. PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Continued)

Fair Value (Continued)

Recurring Fair Value Measures - Activity in Level 3


Recurring Fair Value Measures
Activity in Level 3						Real Estate
Millions
Balance as of December 31, 2022						$22.4
Actual Return on Plan Assets						(3.1)
Purchases, Sales, and Settlements – Net						(0.4)
Balance as of December 31, 2023						$18.9


Recurring Fair Value Measures
Activity in Level 3									Real Estate
Millions
Balance as of December 31, 2021									$21.6
Actual Return on Plan Assets									1.0
Purchases, Sales, and Settlements – Net									(0.2)
Balance as of December 31, 2022									$22.4


Recurring Fair Value Measures
Activity in Level 3			Private Equity Funds
Millions
Balance as of December 31, 2021			$2.0
Actual Return on Plan Assets			(1.5)
Purchases, Sales, and Settlements – Net			(0.5)
Balance as of December 31, 2022			—

Income Tax Expense - Narrative (Details) - USD ($)	12 Months Ended
Income Tax Expense - Narrative (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
NOL and Tax Credit Carryforwards [Line Items]
Effective tax rate	13.50%	(31.20%)	(24.30%)
Net unrecognized tax benefits	$ 600,000
Accrued interest	100,000	$ 0	$ 0
Penalties	0	$ 0	$ 0
Material changes to unrecognized tax benefits expected during next 12 months	0
Federal
NOL and Tax Credit Carryforwards [Line Items]
Valuation allowance	$ 0

Property, Plant and Equipment - Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Asset Retirement Obligation [Roll Forward]
Beginning obligation	$ 200.4	$ 184.5
Accretion	10.3	9.5
Liabilities Recognized		7.8
Liabilities Settled	(10.2)	(4.4)
Revisions in Estimated Cash Flows	2.4	3.0
Ending obligation	$ 202.9	$ 200.4

Short-Term and Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Long-term Debt


Long-Term Debt
As of December 31	2023	2022
Millions
First Mortgage Bonds
6.02% Series Due 2023	—	$75.0
3.69% Series Due 2024	$60.0	60.0
4.90% Series Due 2025	30.0	30.0
5.10% Series Due 2025	30.0	30.0
3.20% Series Due 2026	75.0	75.0
5.99% Series Due 2027	60.0	60.0
3.30% Series Due 2028	40.0	40.0
4.08% Series Due 2029	70.0	70.0
3.74% Series Due 2029	50.0	50.0
2.50% Series Due 2030	46.0	46.0
3.86% Series Due 2030	60.0	60.0
2.79% Series Due 2031	100.0	100.0
4.54% Series Due 2032	75.0	75.0
4.98% Series Due 2033	125.0	—
5.69% Series Due 2036	50.0	50.0
6.00% Series Due 2040	35.0	35.0
5.82% Series Due 2040	45.0	45.0
4.08% Series Due 2042	85.0	85.0
4.21% Series Due 2043	60.0	60.0
4.95% Series Due 2044	40.0	40.0
5.05% Series Due 2044	40.0	40.0
4.39% Series Due 2044	50.0	50.0
4.07% Series Due 2048	60.0	60.0
4.47% Series Due 2049	30.0	30.0
3.30% Series Due 2050	94.0	94.0
Armenia Mountain Senior Secured Notes 3.26% Due 2024	9.5	19.3
Industrial Development Variable Rate Demand Refunding Revenue Bonds Series 2006, Due 2025	27.8	27.8
Revolving Credit Facility Variable Rate Due 2027	—	13.0
Senior Unsecured Notes 2.65% Due 2025	150.0	150.0
Senior Unsecured Notes 3.11% Due 2027	80.0	80.0
SWL&P First Mortgage Bonds 4.15% Series Due 2028	15.0	15.0
SWL&P First Mortgage Bonds 4.14% Series Due 2048	12.0	12.0
Unsecured Term Loan Variable Rate Due 2023	—	170.0
Other Long-Term Debt, 2023 Weighted Average Rate 5.24% Due 2024 – 2051	95.1	82.0
Unamortized Debt Issuance Costs	(8.1)	(8.3)
Total Long-Term Debt	1,791.3	1,920.8
Less: Due Within One Year	111.4	272.6
Net Long-Term Debt	$1,679.9	$1,648.2

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

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+ Details

Operations and Significant Accounting Policies - Other Non-Current Assets (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Contract asset - noncurrent	$ 18.5	$ 21.0
ALLETE Properties	10.8	19.1
Restricted Cash	2.4	2.3	$ 2.3
Other Postretirement Benefit Plans	106.3	58.8
Other	124.9	103.1
Total Other Non-Current Assets	$ 262.9	$ 204.3

Consolidated Statement of Comprehensive Income Parentheticals - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Net of Income Tax Expense (Benefit) of $0.1, $(0.2) and $(0.1)	$ 0.1	$ (0.2)	$ (0.1)
Net of Income Tax Expense (Benefit) of $2.4, $(0.1) and $3.0	$ 2.4	$ (0.1)	$ 3.0

Operations and Significant Accounting Policies - Supplemental Statement of Cash Flows Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash Paid During the Period for Interest – Net of Amounts Capitalized	$ 80.5	$ 72.8	$ 66.8
Cash Paid for Income Taxes	19.5	6.0	0.0
Noncash Investing and Financing Activities
Increase (Decrease) in Accounts Payable for Capital Additions to Property, Plant and Equipment	2.2	(9.6)	(14.0)
Reclassification of Property, Plant and Equipment to Inventory	0.0	99.7	0.0
Reclassification of Redeemable Non-Controlling Interest to Current Liabilities	0.0	0.0	30.6
Capitalized Asset Retirement Costs	5.8	11.8	16.9
AFUDC–Equity	$ 3.6	$ 2.7	$ 2.6

Pay vs Performance Disclosure - USD ($) $ in Millions	3 Months Ended												12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Millions	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net Income Attributable to ALLETE	$ 51.5	$ 85.9	$ 51.5	$ 58.2	$ 51.7	$ 33.7	$ 37.6	$ 66.3	$ 61.9	$ 27.6	$ 27.9	$ 51.8	$ 247.1	$ 189.3	$ 169.2

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details

Consolidated Statement of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Activities
Net Income	$ 178.9	$ 131.3	$ 137.8
Adjustments to Reconcile Net Income to Cash provided by Operating Activities:
AFUDC – Equity	(3.6)	(2.7)	(2.6)
Income from Equity Investments – Net of Dividends	1.0	2.4	2.2
(Gain) / Loss on Investments and Property, Plant and Equipment	0.0	1.2	(0.8)
Depreciation Expense	251.7	242.0	231.6
Amortization of PSAs	(5.2)	(7.6)	(11.4)
Amortization of Other Intangible Assets and Other Assets	7.1	8.3	9.9
Deferred Income Tax Expense (Benefit)	17.6	(38.5)	(26.9)
Share-Based and ESOP Compensation Expense	7.3	4.9	5.9
Defined Benefit Pension and Other Postretirement Plan Expense (Benefit)	(6.1)	(3.0)	4.3
Bad Debt Expense	1.3	1.9	1.2
Fuel Adjustment Clause	44.0	15.1	(56.4)
Provision (Payments) for Interim Rate Refund	(18.4)	18.4	0.0
Changes in Operating Assets and Liabilities
Accounts Receivable	1.8	(14.0)	(13.0)
Inventories	277.1	(256.1)	(23.5)
Prepayments and Other	(7.9)	(21.5)	(0.5)
Accounts Payable	(4.0)	(1.3)	15.0
Other Current Liabilities	(157.6)	116.2	28.0
Cash Contributions to Defined Benefit Pension Plans	(17.3)	0.0	(10.3)
Changes in Regulatory and Other Non-Current Assets	15.6	24.1	(12.0)
Changes in Regulatory and Other Non-Current Liabilities	2.0	0.2	(15.0)
Cash provided by Operating Activities	585.3	221.3	263.5
Investing Activities
Proceeds from Sale of Available-for-sale Securities	1.0	2.2	6.4
Payments for Purchase of Available-for-sale Securities	(1.2)	(2.4)	(3.6)
Acquisitions of Subsidiaries – Net of Cash and Restricted Cash Acquired	0.0	(155.0)	0.0
Payments for Equity Investments	(8.2)	(5.9)	(17.6)
Additions to Property, Plant and Equipment	(271.2)	(220.5)	(479.5)
Other Investing Activities	(4.0)	(2.4)	9.1
Cash used in Investing Activities	(283.6)	(384.0)	(485.2)
Financing Activities
Proceeds from Issuance of Common Stock	14.9	248.0	69.9
Equity Issuance Costs	0.0	(8.1)	0.0
Proceeds from Issuance of Short-Term and Long-Term Debt	437.0	785.4	733.0
Repayments of Short-Term and Long-Term Debt	(566.7)	(877.0)	(552.9)
Proceeds from Non-Controlling Interest in Subsidiaries – Net of Issuance Costs	17.8	155.7	90.9
Distributions to Non-Controlling Interest	(8.5)	(1.7)	(3.1)
Dividends on Common Stock	(155.5)	(145.9)	(131.9)
Other Financing Activities	(1.5)	(1.2)	(1.7)
Cash provided (used in) by Financing Activities	(262.5)	155.2	204.2
Change in Cash, Cash Equivalents and Restricted Cash	39.2	(7.5)	(17.5)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	40.2	47.7	65.2
Cash, Cash Equivalents and Restricted Cash at End of Period	$ 79.4	$ 40.2	$ 47.7

Consolidated Balance Sheet Parentheticals - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Accounts Receivable [Abstract]
Accounts Receivable (Less Allowance of $1.6 and $1.6 )	$ 1.6	$ 1.6
Common Stock [Abstract]
Common stock, shares authorized (in shares)	80,000,000.0	80,000,000.0
Common stock, shares issued (in shares)	57,600,000	57,200,000
Common stock, shares outstanding (in shares)	57,600,000	57,200,000

Income Tax Expense - Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred Income Tax Assets
Employee Benefits and Compensation	$ 29.3	$ 46.4
Property-Related	58.1	61.9
NOL Carryforwards	13.0	16.7
Capital Loss Carryforwards	2.1	13.1
Tax Credit Carryforwards	557.4	548.7
Power Sales Agreements	9.0	13.7
Regulatory Liabilities	89.0	95.5
Other	8.7	28.1
Gross Deferred Income Tax Assets	766.6	824.1
Deferred Income Tax Asset Valuation Allowance	(58.0)	(60.2)
Total Deferred Income Tax Assets	708.6	763.9
Deferred Income Tax Liabilities
Deferred Gain	7.9	7.9
Property-Related	632.0	661.7
Regulatory Asset for Benefit Obligations	48.1	57.7
Unamortized Investment Tax Credits	29.6	30.0
Partnership Basis Differences	156.5	126.0
Fuel Adjustment Clause	1.9	10.7
Regulatory Assets	25.3	28.0
Total Deferred Income Tax Liabilities	901.3	922.0
Net Deferred Income Taxes	$ 192.7	$ 158.1

Operations and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Financial Statement Preparation	Financial Statement Preparation. References in this report to “we,” “us,” and “our” are to ALLETE and its subsidiaries, collectively. We prepare our financial statements in conformity with GAAP. These principles require management to make informed judgments, best estimates, and assumptions that affect the reported amounts of assets, liabilities, revenue and expenses. Actual results could differ from those estimates. The presentation of certain prior period amounts on the Consolidated Financial Statements have been adjusted for comparative purposes.
Subsequent Events	Subsequent Events. The Company performed an evaluation of subsequent events for potential recognition and disclosure through the time of the financial statements issuance.
Principles of Consolidation	Principles of Consolidation. Our Consolidated Financial Statements include the accounts of ALLETE, all of our majority owned subsidiary companies and variable interest entities of which ALLETE is the primary beneficiary. All material intercompany balances and transactions have been eliminated in consolidation.
Variable Interest Entities	Variable Interest Entities. The accounting guidance for “Variable Interest Entities” (VIE) is a consolidation model that considers if a company has a variable interest in a VIE. A VIE is a legal entity that possesses any of the following conditions: the entity’s equity at risk is not sufficient to permit the legal entity to finance its activities without additional subordinated financial support, equity owners are unable to direct the activities that most significantly impact the legal entity’s economic performance (or they possess disproportionate voting rights in relation to the economic interest in the legal entity), or the equity owners lack the obligation to absorb the legal entity’s expected losses or the right to receive the legal entity’s expected residual returns. Entities are required to consolidate a VIE when it is determined that they have a controlling financial interest in a VIE and therefore are the primary beneficiary of that VIE, as defined by the accounting guidance for “Variable Interest Entities.” In determining whether ALLETE is the primary beneficiary of a VIE, management considers whether ALLETE has the power to direct the most significant activities of the VIE and is obligated to absorb losses or receive the expected residual returns that are significant to the VIE. The accounting guidance for VIEs applies to certain ALLETE Clean Energy wind energy facilities, certain New Energy Equity facilities, and our investment in Nobles 2. (See Tax Equity Financing.)
Business Segments	Business Segments. We present two reportable segments: Regulated Operations and ALLETE Clean Energy. Our segments were determined in accordance with the guidance on segment reporting. We measure performance of our operations through budgeting and monitoring of contributions to consolidated net income by each business segment. We present two reportable segments: Regulated Operations and ALLETE Clean Energy. We measure performance of our operations through budgeting and monitoring of contributions to consolidated net income by each business segment.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash. We consider all investments purchased with original maturities of three months or less to be cash equivalents. As of December 31, 2023, and 2022, restricted cash amounts included in Prepayments and Other on the Consolidated Balance Sheet include deposits required under a tax equity financing agreement and collateral deposits required under an ALLETE Clean Energy loan agreement. The restricted cash amounts included in Other Non-Current Assets represent collateral deposits required under an ALLETE Clean Energy loan agreement and PSAs.
Accounts Receivable	Accounts Receivable. Accounts receivable are reported on the Consolidated Balance Sheet net of an allowance for doubtful accounts. The allowance is based on our evaluation of the receivable portfolio under current conditions, overall portfolio quality, review of specific situations and such other factors that, in our judgment, deserve recognition in estimating losses.
Long-Term Finance Receivables	Long-Term Finance Receivables. Long-term finance receivables relating to our real estate operations are collateralized by property sold, accrue interest at market-based rates and are net of an allowance for doubtful accounts. We assess delinquent finance receivables by comparing the balance of such receivables to the estimated fair value of the collateralized property. If the fair value of the property is less than the finance receivable, we record a reserve for the difference. We estimate fair value based on recent property tax assessed values or current appraisals.
Available-for-Sale Securities	Available-for-Sale Securities. Available-for-sale debt and equity securities are recorded at fair value. Unrealized gains and losses on available-for-sale debt securities are included in accumulated other comprehensive income (loss), net of tax. Unrealized gains and losses on available-for-sale equity securities are recognized in earnings. We use the specific identification method as the basis for determining the cost of securities sold.
Inventories – Net	Inventories – Net. Inventories are stated at the lower of cost or net realizable value. Inventories in our Regulated Operations segment are carried at an average cost or first-in, first-out basis. Inventories in our ALLETE Clean Energy segment and Corporate and Other businesses are carried at an average cost, first-in, first-out or specific identification basis.
Property, Plant and Equipment	Property, Plant and Equipment. Property, plant and equipment are recorded at original cost and are reported on the Consolidated Balance Sheet net of accumulated depreciation. Expenditures for additions, significant replacements, improvements and major plant overhauls are capitalized; maintenance and repair costs are expensed as incurred. Gains or losses on property, plant and equipment for Corporate and Other operations are recognized when they are retired or otherwise disposed. When property, plant and equipment in our Regulated Operations and ALLETE Clean Energy segments are retired or otherwise disposed, no gain or loss is recognized in accordance with the accounting standards for component depreciation except for certain circumstances where the retirement is unforeseen or unexpected. Our Regulated Operations capitalize AFUDC, which includes both an interest and equity component. AFUDC represents the cost of both debt and equity funds used to finance utility plant additions during construction periods. AFUDC amounts capitalized are included in rate base and are recovered from customers as the related property is depreciated. Upon MPUC approval of cost recovery, the recognition of AFUDC ceases. (See Note 2. Property, Plant and Equipment.) We believe that long-standing ratemaking practices approved by applicable state and federal regulatory commissions allow for the recovery of the remaining book value of retired plant assets. The MPUC order for Minnesota Power’s 2015 IRP directed Minnesota Power to retire Boswell Units 1 and 2, which occurred in the fourth quarter of 2018. As part of the 2016 general retail rate case, the MPUC allowed recovery of the remaining book value of Boswell Units 1 and 2 through 2022. Minnesota Power’s latest IRP, which was approved by the MPUC in an order dated January 9, 2023, includes ceasing coal operations at Boswell Units 3 and 4 by 2030 and 2035, respectively. Boswell Unit 3 and Unit 4 have a net book value of approximately $220 million and $420 million, respectively, as of December 31, 2023. (See Note 4. Regulatory Matters.) Minnesota Power also retired Taconite Harbor in the first quarter of 2023 consistent with its latest IRP. As part of the 2022 general retail rate case, the MPUC allowed recovery of the remaining book value of Taconite Harbor through 2026. We do not expect to record any impairment charge as a result of these operating changes at Taconite Harbor and Boswell. In addition, we expect to be able to continue depreciating these assets for at least their established remaining useful lives; however, we are unable to predict the impact of regulatory outcomes resulting in changes to their established remaining useful lives.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets. We review our long-lived assets for indicators of impairment in accordance with the accounting standards for property, plant and equipment on a quarterly basis. This includes our property, plant and equipment (see Property, Plant and Equipment) and land inventory. Land inventory is accounted for as held for use and is recorded at cost, unless the carrying value is determined not to be recoverable in accordance with the accounting standards for property, plant and equipment, in which case the land inventory is written down to estimated fair value. In accordance with the accounting standards for property, plant and equipment, if indicators of impairment exist, we test our long lived assets for recoverability by comparing the carrying amount of the asset to the undiscounted future net cash flows expected to be generated by the asset. Cash flows are assessed at the lowest level of identifiable cash flows. The undiscounted future net cash flows are impacted by trends and factors known to us at the time they are calculated, and our expectations related to: management’s best estimate of future use; sales prices; holding period and timing of sales; method of disposition; and future expenditures necessary to maintain the operations.
Derivatives	Derivatives. ALLETE is exposed to certain risks relating to its business operations that can be managed through the use of derivative instruments. ALLETE may enter into derivative instruments to manage those risks including interest rate risk related to certain variable-rate borrowings, and commodity price and transmission congestion cost risk related to sales to electric customers. We have determined that either these agreements are immaterial to the financial statements, are not derivatives, or, if they are derivatives, the agreements qualify for the normal purchases and normal sales exception to derivative accounting guidance; therefore, derivative accounting is not required.
Accounting for Stock-Based Compensation	Accounting for Stock-Based Compensation. We apply the fair value recognition guidance for share-based payments. Under this guidance, we recognize stock-based compensation expense for all share-based payments granted, net of an estimated forfeiture rate. (See Note 13. Employee Stock and Incentive Plans.) Performance Shares. Under the performance share awards, the number of shares earned is contingent upon attaining specific market and performance goals over a three-year performance period. Market goals are measured by total shareholder return relative to a group of peer companies while performance goals are measured by earnings per share growth. In the case of qualified retirement, death, or disability during a performance period, a pro rata portion of the award will be earned at the conclusion of the performance period based on the market goals achieved. In the case of termination of employment for any reason other than qualified retirement, death, or disability, no award will be earned. If there is a change in control, a pro rata portion of the award will be paid based on the greater of actual performance up to the date of the change in control or target performance. The fair value of these awards incorporates the probability of meeting the total shareholder return goals. Compensation cost is recognized over the three-year performance period based on our estimate of the number of shares which will be earned by the award recipients. Restricted Stock Units. Under the restricted stock unit awards, shares for participants eligible for retirement vest monthly over a three-year period. For participants not eligible for retirement, shares vest at the end of the three-year period. In the case of qualified retirement, death or disability, a pro rata portion of the award will be earned. In the case of termination of employment for any reason other than qualified retirement, death or disability, no award will be earned. If there is a change in control, a pro rata portion of the award will be earned. The fair value of these awards is equal to the grant date fair value. Compensation cost is recognized over the three-year vesting period based on our estimate of the number of shares which will be earned by the award recipients. Employee Stock Purchase Plan (ESPP). Under our ESPP, eligible employees may purchase ALLETE common stock at a 5 percent discount from the market price; we are not required to apply fair value accounting to these awards as the discount is not greater than 5 percent. RSOP. The RSOP is a contributory defined contribution plan subject to the provisions of the Employee Retirement Income Security Act of 1974, as amended, and qualifies as an employee stock ownership plan and profit sharing plan. The RSOP provides eligible employees an opportunity to save for retirement.
Goodwill	Goodwill. Goodwill is the excess of the purchase price (consideration transferred) over the estimated fair value of net assets of acquired businesses. In accordance with GAAP, goodwill is not amortized. Goodwill is assessed annually in the fourth quarter for impairment and whenever an event occurs or circumstances change that would indicate the carrying amount may be impaired. Impairment testing for goodwill is done at the reporting unit level.
Leases	Leases. We determine if a contract is, or contains, a lease at inception and recognize a right-of-use asset and lease liability for all leases with a term greater than 12 months. Our right-of-use assets and lease liabilities for operating and finance leases are included in Other Non-Current Assets, Other Current Liabilities and Other Non-Current Liabilities, respectively, in our Consolidated Balance Sheet. Right-of-use assets represent our right to use an underlying asset for the lease term and lease liabilities represent the obligation to make lease payments arising from the lease. Operating and finance lease right-of-use assets and lease liabilities are recognized at the commencement date based on the estimated present value of lease payments over the lease term. As our leases do not provide an explicit rate, we determine the present value of future lease payments based on our estimated incremental borrowing rate using information available at the lease commencement date. The operating and finance lease right-of-use assets includes lease payments to be made during the lease term and any lease incentives, as applicable. Our leases may include options to extend or buy out the lease at certain points throughout the term, and if it is reasonably certain at lease commencement that we will exercise that option, we include those rental payments in our calculation of the right-of-use asset and lease liability. Lease and rent expense are recognized on a straight-line basis over the lease term for operating leases. Finance leases recognize interest expense using the interest expense method over the lease term and amortization expense on a straight-line basis over the shorter of the useful life of the asset or the lease term, unless a buy out option is reasonably certain to be exercised, for which we then amortize on a straight-line basis over the useful life of the asset. Leases with a term of 12 months or less are not recognized on the Consolidated Balance Sheet. The majority of our operating leases are for heavy equipment, vehicles and land with fixed monthly payments which we group into two categories: Vehicles and Equipment; and Land and Other. Our largest operating lease is for the drag line at BNI Energy which includes a termination payment at the end of the lease term if we do not exercise our purchase option. The amount of this payment is $3 million and is included in our calculation of the right-of-use asset and lease liability recorded. None of our other leases contain residual value guarantees. We have one finance lease for heavy equipment which includes a purchase option we are reasonably certain to exercise when the lease terminates.
Environmental Liabilities	Environmental Liabilities. We review environmental matters on a quarterly basis. Accruals for environmental matters are recorded when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated based on current law and existing technologies. Accruals are adjusted as assessment and remediation efforts progress, or as additional technical or legal information becomes available. Accruals for environmental liabilities are included in the Consolidated Balance Sheet at undiscounted amounts and exclude claims for recoveries from insurance or other third parties. Costs related to environmental contamination treatment and cleanup are expensed unless recoverable in rates from customers. (See Note 9. Commitments, Guarantees and Contingencies.) We review environmental matters on a quarterly basis. Accruals for environmental matters are recorded when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated based on current law and existing technologies. Accruals are adjusted as assessment and remediation efforts progress, or as additional technical or legal information becomes available. Accruals for environmental liabilities are included in the Consolidated Balance Sheet at undiscounted amounts and exclude claims for recoveries from insurance or other third parties. Costs related to environmental contamination treatment and cleanup are expensed unless recoverable in rates from customers.
Revenue Recognition	Revenue. Contracts with Customers – Utility includes sales from our regulated operations for generation, transmission and distribution of electric service, and distribution of water and gas services to our customers. Also included is an immaterial amount of regulated steam generation that is used by customers in the production of paper and pulp. Contracts with Customers – Non-utility includes sales of goods and services to customers from ALLETE Clean Energy and our Corporate and Other businesses. Other – Non-utility is the non-cash adjustments to revenue recognized by ALLETE Clean Energy for the amortization of differences between contract prices and estimated market prices for PSAs that were assumed during the acquisition of various wind energy facilities. Revenue Recognition. Revenue is recognized upon transfer of control of promised goods or services to our customers in an amount that reflects the consideration we expect to receive in exchange for those products or services. Revenue is recognized net of allowance for returns and any taxes collected from customers, which are subsequently remitted to the appropriate governmental authorities. We account for shipping and handling activities that occur after the customer obtains control of goods as a cost rather than an additional performance obligation thereby recognizing revenue at time of shipment and accruing shipping and handling costs when control transfers to our customers. We have a right to consideration from our customers in an amount that corresponds directly with the value to the customer for our performance completed to date; therefore, we may recognize revenue in the amount to which we have a right to invoice. NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued) Revenue (Continued) Nature of Revenue Streams Utility Residential and Commercial includes sales for electric, gas or water service to customers, who have implied contracts with the utility, under rates governed by the MPUC, PSCW or FERC. Customers are billed on a monthly cycle basis and revenue is recognized for electric, gas or water service delivered during the billing period. Revenue is accrued for service provided but not yet billed at period end. Performance obligations with these customers are satisfied at time of delivery to customer meters and simultaneously consumed. Municipal includes sales to 14 non-affiliated municipal customers in Minnesota under long-term wholesale electric contracts. One of these wholesale electric contracts include a termination clause requiring a three-year notice to terminate. These contracts have termination dates ranging through 2037, with a majority of contracts expiring in 2029. Performance obligations with these customers are satisfied at the time energy is delivered to an agreed upon municipal substation or meter. Industrial includes sales recognized from contracts with customers in the taconite mining, paper, pulp and secondary wood products, pipeline and other industries. Industrial sales accounted for approximately 55 percent of total regulated utility kWh sales for the year ended December 31, 2023. Within industrial revenue, Minnesota Power had eight Large Power Customer contracts, each serving requirements of 10 MW or more of customer load as of December 31, 2023. These contracts automatically renew past the contract term unless a four-year written notice is given. Large Power Customer contracts have earliest termination dates ranging from 2027 through 2029. We satisfy our performance obligations for these customers at the time energy is delivered to an agreed upon customer substation. Revenue is accrued for energy provided but not yet billed at period end. Based on current contracts with industrial customers, we expect to recognize minimum revenue for the fixed contract components of approximately $62 million per annum through 2027, $15 million in 2028, and $12 million in total thereafter, which reflects the termination notice period in these contracts. When determining minimum revenue, we assume that customer contracts will continue under the contract renewal provision; however, if long-term contracts are renegotiated and subsequently approved by the MPUC or there are changes within our industrial customer class, these amounts may be impacted. Contracts with customers that contain variable pricing or quantity components are excluded from the expected minimum revenue amounts. Other Power Suppliers includes the sale of energy under a long-term PSA with one customer as well as MISO market and liquidation sales. The expiration date of this PSA is 2028. Performance obligations with these customers are satisfied at the time energy is delivered to an agreed upon delivery point defined in the contract (generally the MISO pricing node). The current contract with one customer contains variable pricing components that prevent us from estimating future minimum revenue. Other Revenue includes all remaining individually immaterial revenue streams for Minnesota Power and SWL&P, and is comprised of steam sales to paper and pulp mills, wheeling revenue and other sources. Revenue for steam sales to customers is recognized at the time steam is delivered and simultaneously consumed. Revenue is recognized at the time each performance obligation is satisfied. CIP Financial Incentive reflects certain revenue that is a result of the achievement of certain objectives for our CIP financial incentives. This revenue is accounted for in accordance with the accounting standards for alternative revenue programs which allow for the recognition of revenue under an alternative revenue program if the program is established by an order from the utility’s regulatory commission, the order allows for automatic adjustment of future rates, the amount of revenue recognized is objectively determinable and probable of recovery, and the revenue will be collected within 24 months following the end of the annual period in which it is recognized. CIP financial incentives are recognized in the period in which the MPUC approves the filing, which is typically mid-year. NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued) Revenue (Continued) Non-utility ALLETE Clean Energy Long-term PSA revenue includes all sales recognized under long-term contracts for production, curtailment, capacity and associated renewable energy credits from ALLETE Clean Energy wind energy facilities. Expiration dates of these PSAs range from 2024 through 2039. Performance obligations for these contracts are satisfied at the time energy is delivered to an agreed upon point, or production is curtailed at the request of the customer, at specified prices. Revenue from the sale of renewable energy credits is recognized at the same time the related energy is delivered to the customer when sold to the same party. Sale of Wind Energy Facility includes revenue recognized for the design, development, construction, and sale of a wind energy facility to a customer. Performance obligations for these types of agreements are satisfied at the time the completed project is transferred to the customer at the commercial operation date. Revenue from the sale of a wind energy facility is recognized at the time of asset transfer. Other is the non-cash adjustments to revenue recognized by ALLETE Clean Energy for the amortization of differences between contract prices and estimated market prices on assumed PSAs. As part of wind energy facility acquisitions, ALLETE Clean Energy assumed various PSAs that were above or below estimated market prices at the time of acquisition; the resulting differences between contract prices and estimated market prices are amortized to revenue over the remaining PSA term. Corporate and Other Long-term Contract encompasses the sale and delivery of coal to customer generation facilities. Revenue is recognized on a monthly basis at the cost of production plus a specified profit per ton of coal delivered to the customer. Coal sales are secured under long-term coal supply agreements extending through 2037. Performance obligations are satisfied during the period as coal is delivered to customer generation facilities. Sale of Renewable Development Projects includes revenue recognized from development only and development plus construction type projects that are sold to a customer. For development only projects, revenue is recognized at point in time when all required development responsibilities have been completed and ownership has transferred to the customer. For development plus construction, the transaction price is allocated to two performance obligations based upon the standalone selling price of each obligation. Revenue is recognized on the development performance obligation upon satisfying all required development activities and ownership transferring to the customer. Revenue for the construction performance obligation is recognized over time based on construction costs incurred, beginning at notice to proceed through the commercial operation date. Other primarily includes revenue from BNI Energy unrelated to coal, revenue from New Energy for asset management services and non-development activities, the sale of real estate from ALLETE Properties, and non‑rate base steam generation that is sold for use during production of paper and pulp. Performance obligations are satisfied when control transfers to the customer. Payment Terms. Payment terms and conditions vary across our businesses. Aside from taconite-producing Large Power Customers, payment terms generally require payment to be made within 15 to 30 days from the end of the period that the service has been rendered. In the case of its taconite-producing Large Power Customers, as permitted by the MPUC, Minnesota Power requires weekly payments for electric usage based on monthly energy usage estimates. These customers receive estimated bills based on Minnesota Power’s estimate of the customers’ energy usage, forecasted energy prices and fuel adjustment clause estimates. Minnesota Power’s taconite-producing Large Power Customers have generally predictable energy usage on a weekly basis and any differences that occur are trued-up the following month. Due to the timing difference of revenue recognition from the timing of invoicing and payment, the taconite-producing Large Power Customers receive credit for the time value of money; however, we have determined that our contracts do not include a significant financing component as the period between when we transfer the service to the customer and when they pay for such service is minimal. NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued) Revenue (Continued) Assets Recognized From the Costs to Obtain a Contract with a Customer. We recognize as an asset the incremental costs of obtaining a contract with a customer if we expect the benefit of those costs to be longer than one year. We expense incremental costs when the asset that would have resulted from capitalizing these costs would have been amortized in one year or less. As of December 31, 2023, we have $18.5 million of assets recognized for costs incurred to obtain contracts with our customers ($21.0 million as of December 31, 2022). Management determined the amount of costs to be recognized as assets based on actual costs incurred and paid to obtain and fulfill these contracts to provide goods and services to our customers. Assets recognized to obtain contracts are amortized on a straight-line basis over the contract term as a non-cash reduction to revenue. We recognized $2.4 million of non-cash amortization for the year ended December 31, 2023 ($2.4 million for the year end December 31, 2022).
Unamortized Discount and Premium on Debt	Unamortized Discount and Premium on Debt. Discount and premium on debt are deferred and amortized over the terms of the related debt instruments using a method which approximates the effective interest method.
Non-Controlling Interest in Subsidiaries and Redeemable Non-Controlling Interest	Non-Controlling Interest in Subsidiaries and Redeemable Non-Controlling Interest. Non-controlling interest in subsidiaries and redeemable non-controlling interest represent the portion of equity ownership, net income (loss), and comprehensive income (loss) in subsidiaries that is not attributable to equity holders of ALLETE. Non-controlling Interest in Subsidiaries as of and for the years ended December 31, 2023 and 2022, are related to the tax equity financings for ALLETE Clean Energy’s 106 MW Glen Ullin, 80 MW South Peak, 303 MW Diamond Spring and 303 MW Caddo wind energy facilities as well as ALLETE’s equity investment in the 250 MW Nobles 2 wind energy facility. Redeemable Non-Controlling Interest as of and for the year ended December 31, 2023, is related to a tax equity financing entered into in the fourth quarter of 2023 for certain New Energy solar energy facilities totaling 14 MW. This tax equity financing is classified as redeemable non-controlling interest as the redemption price and date are fixed and determinable. For those wind and solar projects with tax equity financings where the economic benefits are not allocated based on the underlying ownership percentage interests, we have determined that the appropriate methodology for calculating the non-controlling interest in subsidiaries balance is the hypothetical liquidation at book value (HLBV) method. The HLBV method is a balance sheet approach which reflects the substantive economic arrangements in the tax equity financing structures. Under the HLBV method, amounts reported as non-controlling interest in subsidiaries on the Consolidated Balance Sheet represent the amounts the third-party investors would hypothetically receive at each balance sheet reporting date under the liquidation provisions of the LLC agreements, assuming the net assets of the wind and solar projects were liquidated at amounts determined in accordance with GAAP and distributed to the third-party investor and sponsor. The resulting non-controlling interest in subsidiaries balance in these projects is reported as a component of equity on the Consolidated Balance Sheet as either Non-Controlling Interest in Subsidiaries or Redeemable Non-Controlling Interest. NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued) The results of operations for these projects attributable to non-controlling interest under the HLBV method is determined as the difference in non-controlling interest in subsidiaries and redeemable non-controlling interest on the Consolidated Balance Sheet at the start and end of each reporting period, after taking into account any capital transactions between the projects and the third-party investors. Factors used in the HLBV calculation include GAAP income, taxable income (loss), tax attributes such as accelerated depreciation, investment tax credits and production tax credits, capital contributions, cash distributions, and the target yield specified in the corresponding LLC agreement. Changes in these factors could have a significant impact on the amounts that third-party investors and sponsors would receive upon a hypothetical liquidation. The use of the HLBV method to allocate income to the non-controlling interest in subsidiaries may create variability in our results of operations as the application of the HLBV method can drive variability in net income or loss attributable to non-controlling interest in subsidiaries from period to period. Immaterial Out-of-Period Adjustment. In the third quarter of 2023, we recognized a $5.7 million increase in Net Loss Attributable to Non-Controlling Interest on the Consolidated Statement of Income for the correction of an error related to the calculation of non-controlling interest in subsidiaries under the hypothetical liquidation at book value method, of which $3.6 million related to 2022. We have evaluated the effect of this out-of-period adjustment for the current reporting period, as well as on the previous interim and annual periods in which they should have been recognized and concluded that this adjustment is not material to any of the periods affected.
Income Taxes	Income Taxes. ALLETE and its subsidiaries file a consolidated federal income tax return as well as combined and separate state income tax returns. We account for income taxes using the liability method in accordance with GAAP for income taxes. Under the liability method, deferred income tax assets and liabilities are established for all temporary differences in the book and tax basis of assets and liabilities, based upon enacted tax laws and rates applicable to the periods in which the taxes become payable. NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued) Due to the effects of regulation on Minnesota Power and SWL&P, certain adjustments made to deferred income taxes are, in turn, recorded as regulatory assets or liabilities. Tax credits are recorded when earned unless there is a requirement to defer the benefit and amortize it over the book depreciable lives of the related property. The requirement to defer and amortize tax credits only applies to federal credits related to public utility property. In accordance with GAAP for uncertainty in income taxes, we are required to recognize in our financial statements the largest tax benefit of a tax position that is “more‑likely‑than‑not” to be sustained on audit, based solely on the technical merits of the position as of the reporting date. The term “more‑likely‑than‑not” means more than 50 percent likely. (See Note 11. Income Tax Expense.) We have established a valuation allowance against certain state NOL, capital loss and tax credits that we do not expect to utilize before their expiration. NOTE 11. INCOME TAX EXPENSE (Continued)
Excise Taxes	Excise Taxes. We collect excise taxes from our customers levied by governmental entities. These taxes are stated separately on the billing to the customer and recorded as a liability to be remitted to the governmental entity. We account for the collection and payment of these taxes on a net basis.
New Accounting Standards	New Accounting Standards. Improvements to Reportable Segment Disclosures. In November 2023, the FASB issued Accounting Standards Update 2023-07, Improvements to Reportable Segment Disclosures (ASU 2023-07). ASU 2023-07 requires that an entity provide enhanced disclosures about significant segment expenses that are regularly provided to the chief operating decision maker, among other disclosures. ASU 2023-07 is effective for annual periods beginning after December 15, 2023, and for interim periods within annual periods beginning after December 15, 2024, with early adoption permitted. Improvements to Income Tax Disclosures. In December 2023, the FASB issued Accounting Standards Update 2023-09, Improvements to Income Tax Disclosures (ASU 2023-09). ASU 2023-09 was issued to enhance the transparency and decision usefulness of income tax disclosures by disclosing specific categories in the rate reconciliation as well as providing additional information for reconciling items above a threshold. It also requires disclosure about certain income taxes paid. ASU 2023-09 is effective for annual periods beginning after December 15, 2024, with early adoption permitted. There are no other new accounting standards that we anticipate having a material effect on the presentation of ALLETE’s consolidated financial statements.
Asset Retirement Obligations	Asset Retirement Obligations. We recognize, at fair value, obligations associated with the retirement of certain tangible, long lived assets that result from the acquisition, construction, development or normal operation of the asset. Asset retirement obligations (AROs) relate primarily to the decommissioning of our coal-fired and wind energy facilities, and land reclamation at BNI Energy. AROs are included in Other Non-Current Liabilities on the Consolidated Balance Sheet. The associated retirement costs are capitalized as part of the related long-lived asset and depreciated over the useful life of the asset. Removal costs associated with certain distribution and transmission assets have not been recognized, as these facilities have indeterminate useful lives. Conditional asset retirement obligations have been identified for treated wood poles and remaining polychlorinated biphenyl and asbestos-containing assets; however, the period of remediation is indeterminable and removal liabilities have not been recognized. Long-standing ratemaking practices approved by applicable state and federal regulatory authorities have allowed provisions for future plant removal costs in depreciation rates. These plant removal cost recoveries are classified either as AROs or as a regulatory liability for non-AROs. To the extent annual accruals for plant removal costs differ from accruals under approved depreciation rates, a regulatory asset has been established in accordance with GAAP for AROs. (See Note 4. Regulatory Matters.)
Depreciation	Depreciation is computed using the straight-line method over the estimated useful lives of the various classes of assets.
Regulatory Assets and Liabilities	Regulatory Assets and Liabilities. Our regulated utility operations are subject to accounting standards for the effects of certain types of regulation. Regulatory assets represent incurred costs that have been deferred as they are probable for recovery in customer rates. Regulatory liabilities represent obligations to make refunds to customers and amounts collected in rates for which the related costs have not yet been incurred. The Company assesses quarterly whether regulatory assets and liabilities meet the criteria for probability of future recovery or deferral. With the exception of the regulatory asset for Boswell Units 1 and 2 net plant and equipment, no other regulatory assets are currently earning a return. The recovery, refund or credit to rates for these regulatory assets and liabilities will occur over the periods either specified by the applicable regulatory authority or over the corresponding period related to the asset or liability.
Acquisitions	The acquisition was accounted for as a business combination and the purchase price was allocated based on the estimated fair values of the assets acquired and the liabilities assumed at the date of acquisition. The allocation of the purchase price, which was finalized in the fourth quarter of 2022, is shown in the following table. Fair value measurements were valued primarily using the discounted cash flow method and replacement cost basis.
Fair Value	FAIR VALUEFair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). We utilize market data or assumptions that market participants would use in pricing the asset or liability, including assumptions about risk and the risks inherent in the inputs to the valuation technique. These inputs can be readily observable, market corroborated, or generally unobservable. We primarily apply the market approach for recurring fair value measurements and endeavor to utilize the best available information. Accordingly, we utilize valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. These inputs, which are used to measure fair value, are prioritized through the fair value hierarchy.Each asset and liability is classified based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement requires judgment, which may affect the valuation of these assets and liabilities and their placement within the fair value hierarchy levels. The estimated fair value of Cash and Cash Equivalents listed on the Consolidated Balance Sheet approximates the carrying amount and therefore is excluded from the recurring fair value measures in the following tables.Non-financial assets such as equity method investments, goodwill, intangible assets, and property, plant and equipment are measured at fair value when there is an indicator of impairment and recorded at fair value only when an impairment is recognized. Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). We utilize market data or assumptions that market participants would use in pricing the asset or liability, including assumptions about risk and the risks inherent in the inputs to the valuation technique. These inputs can be readily observable, market corroborated, or generally unobservable. We primarily apply the market approach for recurring fair value measurements and endeavor to utilize the best available information. Accordingly, we utilize valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. These inputs, which are used to measure fair value, are prioritized through the fair value hierarchy. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurement) and the lowest priority to unobservable inputs (Level 3 measurement). (See Note 7. Fair Value.)
Fair Value Transfers	The Company’s policy is to recognize transfers in and transfers out of levels as of the actual date of the event or change in circumstances that caused the transfer.
Equity Method Investments	The Company assesses our equity investments in ATC and Nobles 2 for impairment whenever events or changes in circumstances indicate that the carrying amount of our investments may not be recoverable.
Unrecognized Tax Benefits	Unrecognized tax benefits are the differences between a tax position taken or expected to be taken in a tax return and the benefit recognized and measured pursuant to the “more-likely-than-not” criteria. The unrecognized tax benefit balance includes permanent tax positions which, if recognized, would affect the annual effective income tax rate. In addition, the unrecognized tax benefit balance includes temporary tax positions for which the ultimate deductibility is highly certain but for which there is uncertainty about the timing of such deductibility. A change in the period of deductibility would not affect the effective tax rate but would accelerate the payment of cash to the taxing authority to an earlier period.We classify interest related to unrecognized tax benefits as interest expense and tax-related penalties in operating expenses on the Consolidated Statement of Income.The unrecognized tax benefit amounts have been presented as an increase to the net deferred tax liability on the Consolidated Balance Sheet.
Property, Plant and Equipment	Property, Plant and Equipment. The Company assesses the impairment of property, plant, and equipment whenever events or changes in circumstances indicate that the carrying amount of property, plant, and equipment assets may not be recoverable.
Pension and Other Postretirement Benefit Plans	Management considers various factors when making funding decisions such as regulatory requirements, actuarially determined minimum contribution requirements and contributions required to avoid benefit restrictions for the pension plans. Contributions are based on estimates and assumptions which are subject to change Accounting for defined benefit pension and other postretirement benefit plans requires that employers recognize on a prospective basis the funded status of their defined benefit pension and other postretirement plans on their balance sheet and recognize as a component of other comprehensive income, net of tax, the gains or losses and prior service costs or credits that arise during the period but are not recognized as components of net periodic benefit cost. The defined benefit pension and postretirement health and life benefit expense (credit) recognized annually by our regulated utilities are expected to be recovered (refunded) through rates filed with our regulatory jurisdictions. As a result, these amounts that are required to otherwise be recognized in accumulated other comprehensive income have been recognized as a long-term regulatory asset (regulatory liability) on the Consolidated Balance Sheet, in accordance with the accounting standards for the effect of certain types of regulation applicable to our Regulated Operations. The defined benefit pension and postretirement health and life benefit expense (credits) associated with our other operations are recognized in accumulated other comprehensive income. NOTE 12. PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Continued) According to the accounting standards for retirement benefits, only assets in the VEBAs are treated as plan assets in the preceding table for the purpose of determining funded status. In establishing the expected long-term rate of return on plan assets, we determine the long-term historical performance of each asset class, adjust these for current economic conditions, and utilizing the target allocation of our plan assets, forecast the expected long-term rate of return. The discount rate is computed using a bond matching study which utilizes a portfolio of high quality bonds that produce cash flows similar to the projected costs of our pension and other postretirement plans. The Company utilizes actuarial assumptions about mortality to calculate the pension and postretirement health and life benefit obligations.
Employee Stock Ownership Plan	Employee Stock Ownership Plan. We sponsor an ESOP within the RSOP. Eligible employees may contribute to the RSOP plan as of their date of hire. The dividends received by the ESOP are distributed to participants. Dividends on allocated ESOP shares are recorded as a reduction of retained earnings. ESOP employer allocations are funded with contributions paid in either cash or the issuance of ALLETE common stock at the Company’s discretion. According to the accounting standards for stock compensation, unallocated shares of ALLETE common stock held and purchased by the ESOP were treated as unearned ESOP shares and not considered outstanding for earnings per share computations. All ESOP shares have been allocated to participants as of December 31, 2023, 2022 and 2021.

Consolidated Statement of Equity - USD ($) $ in Millions	Total	Common Stock	Accumulated Other Comprehensive Loss	Retained Earnings	Non-Controlling Interest in Subsidiaries
Balance, Beginning of Period at Dec. 31, 2020		$ 1,460.9	$ (31.1)	$ 856.0	$ 505.6
Consolidated Statement of Equity [Roll Forward]
Common Stock Issued	$ 51.0	75.8
Unrealized Gain (Loss) on Debt Securities	(0.1)		(0.1)
Defined Benefit Pension and Other Postretirement Plans	7.4		7.4
Net Income Attributable to ALLETE	169.2			169.2
Common Stock Dividends	131.9			(131.9)
Adjustment of Redeemable Non-Controlling Interest				(1.9)
Proceeds from Non-Controlling Interest in Subsidiaries – Net of Issuance Costs					90.9
Net Loss Attributable to Non-Controlling Interest	31.4				(31.4)
Reclassification of Redeemable Non-Controlling Interest to Current Liabilities					(28.8)
Distributions to Non-Controlling Interest					(3.1)
Balance, End of Period at Dec. 31, 2021	2,937.5	1,536.7	(23.8)	891.4	533.2
Balance, Beginning of Period at Dec. 31, 2020	0.0
Redeemable Non-Controlling Interest
Proceeds from Non-Controlling Interest in Subsidiaries	0.0
Net Loss Attributable to Non-Controlling Interest	0.0
Total Redeemable Non-Controlling Interest at Dec. 31, 2021	$ 0.0
Redeemable Non-Controlling Interest
Dividends Per Share of Common Stock (in usd per share)	$ 2.52
Common Stock Issued		244.8
Unrealized Gain (Loss) on Debt Securities	$ (0.4)		(0.4)
Defined Benefit Pension and Other Postretirement Plans	(0.2)		(0.2)
Net Income Attributable to ALLETE	189.3			189.3
Common Stock Dividends	145.9			(145.9)
Adjustment of Redeemable Non-Controlling Interest				0.0
Proceeds from Non-Controlling Interest in Subsidiaries – Net of Issuance Costs					182.9
Net Loss Attributable to Non-Controlling Interest	58.0				(58.0)
Reclassification of Redeemable Non-Controlling Interest to Current Liabilities					0.0
Distributions to Non-Controlling Interest					(1.7)
Balance, End of Period at Dec. 31, 2022	3,348.3	1,781.5	(24.4)	934.8	656.4
Redeemable Non-Controlling Interest
Proceeds from Non-Controlling Interest in Subsidiaries	0.0
Net Loss Attributable to Non-Controlling Interest	0.0
Total Redeemable Non-Controlling Interest at Dec. 31, 2022	$ 0.0
Redeemable Non-Controlling Interest
Dividends Per Share of Common Stock (in usd per share)	$ 2.60
Common Stock Issued		22.2
Unrealized Gain (Loss) on Debt Securities	$ 0.3		0.3
Defined Benefit Pension and Other Postretirement Plans	3.6		3.6
Net Income Attributable to ALLETE	247.1			247.1
Common Stock Dividends	155.5			(155.5)
Adjustment of Redeemable Non-Controlling Interest				0.0
Proceeds from Non-Controlling Interest in Subsidiaries – Net of Issuance Costs					9.9
Net Loss Attributable to Non-Controlling Interest	68.2				(60.8)
Reclassification of Redeemable Non-Controlling Interest to Current Liabilities					0.0
Distributions to Non-Controlling Interest					(8.5)
Balance, End of Period at Dec. 31, 2023	3,406.6	$ 1,803.7	$ (20.5)	$ 1,026.4	$ 597.0
Redeemable Non-Controlling Interest
Proceeds from Non-Controlling Interest in Subsidiaries	7.9
Net Loss Attributable to Non-Controlling Interest	(7.4)
Total Redeemable Non-Controlling Interest at Dec. 31, 2023	$ 0.5
Redeemable Non-Controlling Interest
Dividends Per Share of Common Stock (in usd per share)	$ 2.71

Equity Investments - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
Equity Investments - Narrative (Details) $ in Millions	Sep. 30, 2022 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($) MW	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Equity Investments [Line Items]
Cash Investments			$ 8.2	$ 5.9	$ 17.6
Wind Turbine Generators \| Tenaska \| Nobles 2 PPA \| Minnesota Power
Equity Investments [Line Items]
Generating capacity counterparty owned (MW) \| MW			250
Contract term			20 years
ATC
Equity Investments [Line Items]
Approximate refund for reversal of FERC ROE order	$ 31.0
Approximate refund for reversal of FERC ROE Order, ALLETE's proportionate share	$ 2.4
Basis point incentive adder			50.00%
Approximate reduction in pretax income for FERC proposal to limit incentive adder, ALLETE's proportionate share			$ 1.0
ATC
Equity Investments [Line Items]
Ownership percentage			8.00%
Cash Investments			$ 8.2	$ 5.9
Authorized return on equity			10.02%
Authorized return on equity, including incentive adder			10.52%
ATC \| Forecast
Equity Investments [Line Items]
Expected additional investment		$ 5.8
Nobles 2
Equity Investments [Line Items]
Ownership percentage			49.00%

Equity Investments

12 Months Ended

Dec. 31, 2023

Equity Method Investments and Joint Ventures [Abstract]

Equity Investments

EQUITY INVESTMENTS

Investment in ATC. Our wholly-owned subsidiary, ALLETE Transmission Holdings, owns approximately 8 percent of ATC, a Wisconsin-based utility that owns and maintains electric transmission assets in portions of Wisconsin, Michigan, Minnesota and Illinois. We account for our investment in ATC under the equity method of accounting. In 2023, we invested $8.2 million in ATC. In total, we expect to invest approximately $5.8 million in 2024.


ALLETE’s Investment in ATC
Year Ended December 31	2023	2022
Millions
Equity Investment Beginning Balance	$165.4	$154.5
Cash Investments	8.2	5.9
Equity in ATC Earnings	23.1	19.3
Distributed ATC Earnings	(18.3)	(15.5)

Amortization of the Remeasurement of Deferred Income Taxes	1.3	1.2
Equity Investment Ending Balance	$179.7	$165.4


ATC Summarized Financial Data
Balance Sheet Data
As of December 31	2023	2022
Millions
Current Assets	$115.2	$89.6
Non-Current Assets	6,337.0	5,997.8
Total Assets	$6,452.2	$6,087.4
Current Liabilities	$495.9	$511.9
Long-Term Debt	2,736.0	2,613.0
Other Non-Current Liabilities	585.2	485.8
Members’ Equity	2,635.1	2,476.7
Total Liabilities and Members’ Equity	$6,452.2	$6,087.4


Income Statement Data
Year Ended December 31	2023	2022	2021
Millions
Revenue	$818.9	$751.2	$754.8
Operating Expense	407.6	381.5	376.2
Other Expense	131.7	122.9	113.9
Net Income	$279.6	$246.8	$264.7
ALLETE’s Equity in Net Income	$23.1	$19.3	$21.3

ATC’s authorized return on equity is 10.02 percent, or 10.52 percent including an incentive adder for participation in a regional transmission organization, based on a 2020 FERC order which is subject to various outstanding legal challenges related to the return on equity calculation and refund period ordered by the FERC. In August 2022, the U.S. Court of Appeals for the District of Columbia Circuit vacated and remanded the 2020 FERC order back to FERC. As a result of this decision, ATC recorded a reserve in the third quarter of 2022 for anticipated refunds to its customers for approximately $31 million of which our share was approximately $2.4 million pre-tax. We cannot predict the return on equity FERC will ultimately authorize in the remanded proceeding.

In addition, the FERC issued a Notice of Proposed Rulemaking in April 2021 to limit the 50 basis point incentive adder for participation in a regional transmission organization to only the first three years of membership in such an organization. If this proposal is adopted, our equity in earnings from ATC would be reduced by approximately $1 million pre-tax annually.

NOTE 6. EQUITY INVESTMENTS (Continued)

Investment in Nobles 2. Our subsidiary, ALLETE South Wind, owns a 49 percent equity interest in Nobles 2, the entity that owns and operates a 250 MW wind energy facility in southwestern Minnesota pursuant to a 20-year PPA with Minnesota Power. We account for our investment in Nobles 2 under the equity method of accounting.


ALLETE’s Investment in Nobles 2
Millions
Equity Investment Balance as of December 31, 2022			$157.3

Equity in Nobles 2 Earnings (a)			(1.4)
Distributed Nobles 2 Earnings			(4.4)
Equity Investment Balance as of December 31, 2023			$151.5

(a)The Company also recorded net loss attributable to non-controlling interest of $10.2 million related to its investment in Nobles 2.

Pension and Other Postretirement Benefit Plans - Plan Asset Allocations (Details)	Dec. 31, 2023	Dec. 31, 2022
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Actual Plan Asset Allocations	100.00%	100.00%
Plan Asset Target Allocations	100.00%
Pension \| Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Actual Plan Asset Allocations	57.00%	46.00%
Plan Asset Target Allocations	55.00%
Pension \| Fixed Income Securities
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Actual Plan Asset Allocations	40.00%	50.00%
Plan Asset Target Allocations	41.00%
Pension \| Real Estate
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Actual Plan Asset Allocations	3.00%	4.00%
Plan Asset Target Allocations	4.00%
Postretirement Health and Life
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Actual Plan Asset Allocations	100.00%	100.00%
Plan Asset Target Allocations	100.00%
Postretirement Health and Life \| Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Actual Plan Asset Allocations	67.00%	66.00%
Plan Asset Target Allocations	65.00%
Postretirement Health and Life \| Fixed Income Securities
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Actual Plan Asset Allocations	33.00%	34.00%
Plan Asset Target Allocations	35.00%
Postretirement Health and Life \| Real Estate
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Actual Plan Asset Allocations	0.00%	0.00%
Plan Asset Target Allocations	0.00%

Operations and Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Cash, Cash Equivalents and Restricted Cash

The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Consolidated Balance Sheet that aggregate to the amounts presented in the Consolidated Statement of Cash Flows.


Cash, Cash Equivalents and Restricted Cash
As of December 31	2023	2022	2021
Millions
Cash and Cash Equivalents	$71.9	$36.4	$45.1
Restricted Cash included in Prepayments and Other	5.1	1.5	0.3
Restricted Cash included in Other Non-Current Assets	2.4	2.3	2.3
Cash, Cash Equivalents and Restricted Cash on the Consolidated Statement of Cash Flows	$79.4	$40.2	$47.7

Supplemental Statement of Cash Flows Information

Supplemental Statement of Cash Flow Information.


Consolidated Statement of Cash Flows
Year Ended December 31	2023	2022	2021
Millions
Cash Paid During the Period for Interest – Net of Amounts Capitalized	$80.5	$72.8	$66.8






Cash Paid for Income Taxes	$19.5	$6.0	—
Noncash Investing and Financing Activities
Increase (Decrease) in Accounts Payable for Capital Additions to Property, Plant and Equipment	$2.2	$(9.6)	$(14.0)
Reclassification of Property, Plant and Equipment to Inventory (a)	—	$99.7	—
Reclassification of Redeemable Non-Controlling Interest to Current Liabilities (b)	—	—	$30.6
Capitalized Asset Retirement Costs	$5.8	$11.8	$16.9


AFUDC–Equity	$3.6	$2.7	$2.6

(a)The decommissioning of the existing Northern Wind assets resulted in a reclassification from Property, Plant and Equipment – Net to Inventories – Net in the second quarter of 2022 as they were repowered and subsequently sold to a subsidiary of Xcel Energy Inc. In the third quarter of 2022, safe harbor equipment was transferred to the project entity resulting in an additional reclassification from Property, Plant and Equipment – Net to Inventories – Net.

(b)Amount reclassified to Current Liabilities resulting from the exercise of an option to buy out a non-controlling interest.

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

Accounts Receivable


Accounts Receivable
As of December 31	2023	2022
Millions
Trade Accounts Receivable
Billed	$106.8	$107.1
Unbilled	23.8	29.2
Less: Allowance for Doubtful Accounts	1.6	1.6
Total Trade Accounts Receivable	129.0	134.7
Income Taxes Receivable	8.2	3.2
Total Accounts Receivable	$137.2	$137.9

Inventories – Net


Inventories – Net
As of December 31	2023	2022
Millions
Fuel (a)	$27.2	$33.4
Materials and Supplies	115.7	75.1
Renewable Energy Facilities Under Development (b)	32.5	347.4




Total Inventories – Net	$175.4	$455.9

(a) Fuel consists primarily of coal inventory at Minnesota Power.

(b) Renewable Energy Facilities Under Development consists primarily of project costs related to renewable energy development projects at New Energy. As of December 31, 2022, it consisted primarily of project costs related to ALLETE Clean Energy’s Northern Wind and Red Barn wind projects sold in the first quarter of 2023 and the second quarter of 2023, respectively. (See Other Current Liabilities.)

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

Other Non-Current Assets


Other Non-Current Assets
As of December 31	2023	2022
Millions
Contract Assets (a)	$18.5	$21.0



ALLETE Properties	10.8	19.1
Restricted Cash	2.4	2.3
Other Postretirement Benefit Plans	106.3	58.8
Other	124.9	103.1
Total Other Non-Current Assets	$262.9	$204.3

(a) Contract Assets include payments made to customers as an incentive to execute or extend service agreements. The contract payments are being amortized over the term of the respective agreements as a reduction to revenue.

Other Current Liabilities


Other Current Liabilities
As of December 31	2023	2022
Millions
Customer Deposits (a)	$7.4	$150.7
PSAs	6.0	6.1


Provision for Interim Rate Refund	—	18.4
Manufactured Gas Plant (b)	0.8	14.7




Other	77.7	61.1
Total Other Current Liabilities	$91.9	$251.0

(a) Primarily related to deposits received by ALLETE Clean Energy for the Northern Wind project sold in the first quarter of 2023 and the Red Barn wind project sold in the second quarter of 2023. (See Inventories – Net.)

(b) The manufactured gas plant represents the current liability for remediation of a former manufactured gas plant site located in Superior, Wisconsin, and formerly operated by SWL&P. (See Note 9. Commitments, Guarantees and Contingencies.)

Other Non-Current Liabilities


Other Non-Current Liabilities
As of December 31	2023	2022
Millions
Asset Retirement Obligation (a)	$202.9	$200.4
PSAs	20.9	26.9


Other	40.5	41.7
Total Other Non-Current Liabilities	$264.3	$269.0

(a) The asset retirement obligation is primarily related to our Regulated Operations and is funded through customer rates over the life of the related assets. Additionally, BNI Energy funds its obligation through its cost-plus coal supply agreements for which BNI Energy has recorded a receivable of $37.2 million in Other Non-Current Assets on the Consolidated Balance Sheet as of December 31, 2023 ($32.4 million as of December 31, 2022).

Components of Lease Cost

Additional information on the components of lease cost and presentation of cash flows were as follows:


As December 31	2023	2022
Millions
Operating Lease Cost	$5.0	$6.3
Finance Lease Cost	$0.1	—

Other Information:
Operating Cash Flows From Operating Leases	$5.0	$6.3

Financing Cash Flows From Finance Leases	$0.2	—

Additional information related to leases were as follows:


As of December 31	2023		2022
Millions

Balance Sheet Information Related to Leases:
Operating Lease Other Non-Current Assets	$10.7		$12.7
Finance Lease Other Non-Current Assets	2.1		—
Total Lease Right-of-use Assets	$12.8		$12.7

Operating Lease Other Current Liabilities	$3.0		$3.2
Finance Lease Other Current Liabilities	0.4		—
Operating Lease Other Non-Current Liabilities	7.7		9.3
Finance Lease Other Non-Current Liabilities	1.6		—
Total Lease Liabilities	$12.7		$12.5

Income Statement Information Related to Leases:
Operating Lease Rent Expense	$5.0		$6.3

Finance Lease Amortization Expense	0.1		—
Total Operating and Finance Lease Expenses	$5.1		$6.3

Weighted Average Remaining Lease Term (Years):
Operating Leases - Vehicles and Equipment	3		4
Operating Leases - Land and Other	12		16
Finance Leases - Vehicles and Equipment	5		0


Weighted Average Discount Rate:
Operating Leases - Vehicles and Equipment	4.0	%	3.9	%
Operating Leases - Land and Other	5.0	%	3.9	%
Finance Leases - Vehicles and Equipment	5.4	%	—	%

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

Leases (Continued)

Maturities of Lease Liabilities

Maturities of operating and finance lease liabilities as of December 31, 2023, were as follows:



Millions	Operating	Finance
2024	$3.2	$0.4
2025	3.2	0.4
2026	3.2	0.4
2027	4.1	0.5
2028	0.2	0.6
Thereafter	1.2	—
Total Lease Payments Due	15.1	2.3
Less: Imputed Interest	4.4	0.3
Total Lease Obligations	10.7	2.0
Less: Current Lease Obligations	3.0	0.4
Total Long-term Lease Obligations	$7.7	$1.6

Other Income (Expense) - Other


Other Income (Expense) - Other
Year Ended December 31	2023	2022	2021
Millions
Pension and Other Postretirement Benefit Plan Non-Service Credit (a)	$8.9	$9.8	$6.1
Interest and Investment Income (b)	10.3	—	2.3
AFUDC - Equity	3.6	2.7	2.6
Gain on Land Sales	0.2	—	0.1
PSA Liability (c)	—	10.2	—
Gain on Arbitration Award (d)	58.4	—	—
Other	3.6	(0.3)	(2.4)
Total Other Income (Expense) - Other	$85.0	$22.4	$8.7

(a)These are components of net periodic pension and other postretirement benefit cost other than service cost. (See Note 12. Pension and Other Postretirement Benefit Plans.)

(b)Interest and Investment Income for the year ended December 31, 2023, reflects $5.1 million of interest income related to interest awarded as part of an arbitration ruling involving a subsidiary of ALLETE Clean Energy. (See Note 9. Commitments, Guarantees and Contingencies.)

(c)The gain on removal of the PSA liability for the Northern Wind project upon decommissioning of the legacy wind energy facility assets, which was more than offset by a reserve for an anticipated loss on the sale of the Northern Wind project that was recorded in Cost of Sales - Non-Utility on the Consolidated Statement of Income.

(d)This reflects a gain recognized for the favorable outcome of an arbitration ruling involving a subsidiary of ALLETE Clean Energy. (See Note 9. Commitments, Guarantees and Contingencies.)

Common Stock and Earnings Per Share - Summary of Common Stock (Details) - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Summary of Common Stock [Line Items]
Beginning balance (in shares)	57,200
Ending balance (in shares)	57,600	57,200
Common Stock
Summary of Common Stock [Line Items]
Beginning balance (in shares)	57,237	53,220	52,085
Employee Stock Purchase Plan (in shares)	16	11	17
Invest Direct (in shares)	232	244	263
Share-Based Compensation (in shares)	76	82	73
Equity Issuance Program (in shares)		3,680	782
Ending balance (in shares)	57,561	57,237	53,220
Beginning balance	$ 1,781.5	$ 1,536.7	$ 1,460.9
Employee Stock Purchase Plan	0.8	0.9	0.8
Invest Direct	13.3	14.9	17.5
Share-Based Compensation	8.1	5.3	6.5
Equity Issuance		223.7	51.0
Ending balance	$ 1,803.7	$ 1,781.5	$ 1,536.7

Fair Value (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Recurring Fair Value Measures


	Fair Value as of December 31, 2023
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets:
Investments (a)
Available-for-sale – Equity Securities	$8.7	—	—	$8.7
Available-for-sale – Corporate and Governmental Debt Securities (b)	—	$6.0	—	6.0
Cash Equivalents	5.8	—	—	5.8
Total Fair Value of Assets	$14.5	$6.0	—	$20.5

Liabilities:
Deferred Compensation (c)	—	$16.5	—	$16.5

Total Fair Value of Liabilities	—	$16.5	—	$16.5

(a)Included in Other Non-Current Assets on the Consolidated Balance Sheet.

(b)As of December 31, 2023, the aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year or less was $1.3 million, in one year to less than three years was $3.2 million, in three years to less than five years was $1.0 million and in five or more years was $0.5 million.

(c)Included in Other Non-Current Liabilities on the Consolidated Balance Sheet.


	Fair Value as of December 31, 2022
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets:
Investments (a)
Available-for-sale – Equity Securities	$7.7	—	—	$7.7
Available-for-sale – Corporate and Governmental Debt Securities	—	$5.7	—	5.7
Cash Equivalents	4.2	—	—	4.2
Total Fair Value of Assets	$11.9	$5.7	—	$17.6

Liabilities: (b)
Deferred Compensation	—	$15.0	—	$15.0

Total Fair Value of Liabilities	—	$15.0	—	$15.0

(a)Included in Other Non-Current Assets on the Consolidated Balance Sheet.

(b)Included in Other Non-Current Liabilities on the Consolidated Balance Sheet.

Financial Instruments


Financial Instruments	Carrying Amount	Fair Value
Millions
Short-Term and Long-Term Debt (a)
December 31, 2023	$1,799.4	$1,670.6
December 31, 2022	$1,929.1	$1,782.7

(a) Excludes unamortized debt issuance costs.

Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
Income Tax Expense (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current Income Tax Expense [Abstract]
Federal	$ 9.4	$ 1.2	$ 0.0
State	0.9	6.1	0.0
Total Current Income Tax Expense	10.3	7.3	0.0
Deferred Income Tax Expense (Benefit) [Abstract]
Federal	(6.0)	(32.8)	(37.2)
State	24.0	(5.2)	10.8
Investment Tax Credit Amortization	(0.4)	(0.5)	(0.5)
Total Deferred Income Tax Expense (Benefit)	17.6	(38.5)	(26.9)
Total Income Tax Expense (Benefit)	$ 27.9	$ (31.2)	$ (26.9)

Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended												12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Selected Quarterly Financial Information [Abstract]
Operating Revenue	$ 402.7	$ 378.8	$ 533.4	$ 564.9	$ 425.8	$ 388.3	$ 373.1	$ 383.5	$ 399.0	$ 345.4	$ 335.6	$ 339.2	$ 1,879.8	$ 1,570.7	$ 1,419.2
Operating Income	43.1	36.0	53.5	48.3	33.7	33.4	13.7	53.4	50.0	31.1	28.2	42.0	180.9	134.2	151.3
Net Income Attributable to ALLETE	$ 51.5	$ 85.9	$ 51.5	$ 58.2	$ 51.7	$ 33.7	$ 37.6	$ 66.3	$ 61.9	$ 27.6	$ 27.9	$ 51.8	$ 247.1	$ 189.3	$ 169.2
Basic Earnings Per Share of Common Stock (in usd per share)	$ 0.89	$ 1.50	$ 0.90	$ 1.02	$ 0.90	$ 0.59	$ 0.67	$ 1.24	$ 1.18	$ 0.53	$ 0.53	$ 0.99	$ 4.31	$ 3.38	$ 3.23
Diluted Earnings Per Share of Common Stock (in dollars per share)	$ 0.89	$ 1.49	$ 0.90	$ 1.02	$ 0.90	$ 0.59	$ 0.67	$ 1.24	$ 1.18	$ 0.53	$ 0.53	$ 0.99	$ 4.30	$ 3.38	$ 3.23

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-3

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482635/260-10-55-15

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (e)(4)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-7

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-2

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 60B
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-60B

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-4

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482662/260-10-50-1

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-10

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(25))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Commitments, Guarantees and Contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments, Guarantees and Contingencies

COMMITMENTS, GUARANTEES AND CONTINGENCIES

The following table details the estimated minimum payments for certain long-term commitments as of December 31, 2023:


	2024	2025	2026	2027	2028	Thereafter
Millions

Capital Purchase Obligations	$73.9	$1.6	$9.9	$38.1	—	$10.5
Easements (a)	$8.0	$8.1	$8.1	$8.2	$8.4	$217.7
PPAs (b)	$140.7	$133.8	$136.6	$125.7	$132.4	$937.5
Other Purchase Obligations (c)	$42.9	—	—	—	—	—

(a)Easement obligations represent the minimum payments for our land easement agreements at our wind energy facilities.

(b)Does not include the Oliver Wind I, Oliver Wind II or Nobles 2 PPAs, as Minnesota Power only pays for energy as it is delivered. (See Power Purchase Agreements.)

(c)Consists of long-term service agreements for wind energy facilities and minimum purchase commitments under coal and rail contracts.

Power Purchase and Sales Agreements. Our long-term PPAs have been evaluated under the accounting guidance for variable interest entities. We have determined that either we have no variable interest in the PPAs, or where we do have variable interests, we are not the primary beneficiary; therefore, consolidation is not required. These conclusions are based on the fact that we do not have both control over activities that are most significant to the entity and an obligation to absorb losses or receive benefits from the entity’s performance. Our financial exposure relating to these PPAs is limited to our capacity and energy payments.

These agreements have also been evaluated under the accounting guidance for derivatives. We have determined that either these agreements are not derivatives, or, if they are derivatives, the agreements qualify for the normal purchases and normal sales exception to derivative accounting guidance; therefore, derivative accounting is not required.

Square Butte PPA. Minnesota Power has a PPA with Square Butte that extends through 2026 (Agreement). Minnesota Power is obligated to pay its pro rata share of Square Butte’s costs based on its entitlement to the output of Square Butte’s 455 MW coal fired generating unit. Minnesota Power’s output entitlement under the Agreement is 50 percent for the remainder of the Agreement, subject to the provisions of the Minnkota Power PSA described in the following table. Minnesota Power’s payment obligation will be suspended if Square Butte fails to deliver any power, whether produced or purchased, for a period of one year. Square Butte’s costs consist primarily of debt service, operating and maintenance, depreciation and fuel expenses. As of December 31, 2023, Square Butte had total debt outstanding of $171.8 million. Annual debt service for Square Butte is expected to be approximately $33.5 million in 2024, $29.5 million in 2025, $29.6 million in 2026, and $11.9 million in 2027 of which Minnesota Power’s obligation is 50 percent. Fuel expenses are recoverable through Minnesota Power’s fuel adjustment clause and include the cost of coal purchased from BNI Energy under a long-term contract.

NOTE 9. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued)

Power Purchase and Sales Agreements (Continued)

Minnesota Power’s cost of power purchased from Square Butte during 2023 was $86.2 million ($82.7 million in 2022; $82.4 million in 2021). This reflects Minnesota Power’s pro rata share of total Square Butte costs based on the 50 percent output entitlement. Included in this amount was Minnesota Power’s pro rata share of interest expense of $5.5 million in 2023 ($5.1 million in 2022; $5.8 million in 2021). Minnesota Power’s payments to Square Butte are approved as a purchased power expense for ratemaking purposes by both the MPUC and the FERC.

Minnesota Power has also entered into the following long-term PPAs for the purchase of capacity and energy as of December 31, 2023:

Counterparty

Quantity

Product

Commencement

Expiration

Pricing

PPAs

Calpine Corporation

25 MW

Capacity

June 2019

May 2026

Fixed

Manitoba Hydro

PPA 1

250 MW

Capacity / Energy

June 2020

May 2035

(a)

PPA 2

133 MW

Energy

June 2020

June 2040

Forward Market Prices

Nobles 2

250 MW

Capacity / Energy

December 2020

December 2040

Fixed

Oliver Wind I

(b)

Energy

December 2006

December 2040

Fixed

Oliver Wind II

(b)

Energy

December 2007

December 2040

Fixed

(a)The capacity price was adjusted annually until 2020 by the change in a governmental inflationary index. The energy price is based on a formula that includes an annual fixed component adjusted for the change in a governmental inflationary index and a natural gas index, as well as market prices.

(b)The PPAs provide for the purchase of all output from the 50 MW Oliver Wind I and 48 MW Oliver Wind II wind energy facilities.

Minnesota Power has also entered into the following long-term PSAs for the sale of capacity and energy as of December 31, 2023:

Counterparty

Quantity

Product

Commencement

Expiration

Pricing

PSAs

Basin

PSA 1

(a)

Capacity

June 2022

May 2025

Fixed

PSA 2

100 MW

Capacity

June 2025

May 2028

Fixed

Great River Energy

100 MW

Capacity

June 2022

May 2025

Fixed

Minnkota Power

(b)

Capacity / Energy

June 2014

December 2026

(b)

Oconto Electric Cooperative

25 MW

Capacity / Energy

January 2019

May 2026

Fixed

Silver Bay Power

(c)

Energy

January 2017

December 2031

(d)

(a)The agreement provided for 75 MW of capacity from June 1, 2022, through May 31, 2023, and increased to 125 MW of capacity from June 1, 2023, through May 31, 2025.

(b)Minnesota Power is selling a portion of its entitlement from Square Butte to Minnkota Power, resulting in Minnkota Power’s net entitlement increasing and Minnesota Power’s net entitlement decreasing until Minnesota Power’s share is eliminated at the end of 2025. Of Minnesota Power’s 50 percent output entitlement, it sold to Minnkota Power approximately 37 percent in 2023 (32 percent in 2022 and 28 percent in 2021). (See Square Butte PPA.)

(c)Silver Bay Power supplies approximately 90 MW of load to Northshore Mining, an affiliate of Silver Bay Power.

(d)The energy pricing escalates at a fixed rate annually and is adjusted for changes in a natural gas index.

NOTE 9. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued)

Coal, Rail and Shipping Contracts. Minnesota Power has coal supply agreements providing for the purchase of a significant portion of its coal requirements through December 2025. Minnesota Power also has coal transportation agreements in place for the delivery of a significant portion of its coal requirements through December 2024. The costs of fuel and related transportation costs for Minnesota Power’s generation are recoverable from Minnesota Power’s utility customers through the fuel adjustment clause.

Environmental Matters.

Our businesses are subject to regulation of environmental matters by various federal, state, and local authorities. A number of regulatory changes to the Clean Air Act, the Clean Water Act and various waste management requirements continue to be promulgated by both the EPA and state authorities. Minnesota Power’s facilities are subject to new requirements under many of these regulations. Minnesota Power is reshaping its generation portfolio, over time, to reduce its reliance on coal, has installed cost-effective emission control technology, and advocates for sound science and policy during rulemaking implementation.

We consider our businesses to be in substantial compliance with currently applicable environmental regulations and believe all necessary permits have been obtained. We anticipate that with many new and proposed state and federal environmental regulations and requirements, potential expenditures for future environmental matters may be material and require significant capital investments. Minnesota Power has evaluated various environmental compliance scenarios using possible outcomes of environmental regulations to project power supply trends and impacts on customers.

We review environmental matters on a quarterly basis. Accruals for environmental matters are recorded when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated based on current law and existing technologies. Accruals are adjusted as assessment and remediation efforts progress, or as additional technical or legal information becomes available. Accruals for environmental liabilities are included in the Consolidated Balance Sheet at undiscounted amounts and exclude claims for recoveries from insurance or other third parties. Costs related to environmental contamination treatment and cleanup are expensed unless recoverable in rates from customers.

Air. The electric utility industry is regulated at the federal and state level to address air emissions. Minnesota Power’s thermal generating facilities mainly burn low-sulfur western sub-bituminous coal. All of Minnesota Power’s coal-fired generating facilities are equipped with pollution control equipment such as scrubbers, baghouses, and low NOX technologies. Under currently applicable environmental regulations, these facilities are substantially compliant with emission requirements.

Cross-State Air Pollution Rule (CSAPR). The CSAPR requires certain states in the eastern half of the U.S., including Minnesota, to reduce power plant emissions that contribute to ozone or fine particulate pollution in other states. The CSAPR does not require installation of controls but does require facilities have sufficient allowances to cover their emissions on an annual basis. These allowances are allocated to facilities from each state’s annual budget and can be bought and sold. Based on review of the NOX and SO2 allowances issued and pending issuance, as well as consideration of current rules, we currently expect generation levels and emission rates will result in continued compliance with the CSAPR. Minnesota Power will continue to monitor ongoing CSAPR rulemakings and compliance implementation, including the EPA’s Good Neighbor Rule which modifies certain aspects of the CSAPR’s program scope and extent (see EPA Good Neighbor Plan for 2015 Ozone NAAQS).

National Ambient Air Quality Standards (NAAQS). The EPA is required to review the NAAQS every five years. If the EPA determines that a state’s air quality is not in compliance with the NAAQS, the state is required to adopt plans describing how it will reduce emissions to attain the NAAQS. Minnesota Power actively monitors NAAQS developments, and the EPA is currently reviewing the primary or secondary NAAQS for NOx, SO2, and ozone. On February 7, 2024, the EPA announced a final rule lowering the annual primary standard for particulate matter less than 2.5 microns (PM2.5) from 12 micrograms per cubic meter (ug/m3) to 9 ug/m3, while retaining other existing primary and secondary standards such as those for course particulate matter. The Company is reviewing the new standard to determine potential impacts. Anticipated timelines and compliance costs related to this new standard and other expected NAAQS revisions cannot yet be fully estimated; however, costs could be material. Minnesota Power would seek recovery of additional costs through a rate proceeding.

NOTE 9. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued)

Environmental Matters (Continued)

EPA Good Neighbor Plan for 2015 Ozone NAAQS. On June 5, 2023, after disapproving state implementation plans, the EPA published a final Federal Implementation Plan (FIP) rule in the Federal Register, the Good Neighbor Plan, to address regional ozone transport for the 2015 Ozone NAAQS by reducing NOx emissions during the period of May 1 through September 30 (ozone season). In its justification for the final rule, the EPA asserted that 23 states, including Minnesota, were modeled as significant contributors to downwind states’ challenges in attaining or maintaining ozone NAAQS compliance. The Good Neighbor Plan is designed to resolve this interstate transport issue by implementing a variety of NOx reduction strategies, including federal implementation plan requirements, NOx emission limitations, and ozone season allowance program requirements. The final rule imposed restrictions on fossil-fuel fired power plants in 22 states and on certain industrial sources in 20 states, with implementation occurring through changes to the existing CSAPR program for power plants.

Since the EPA partially disapproved the Good Neighbor State Implementation Plans (SIPs) for the states of Minnesota and Wisconsin, among others, Minnesota is subject to the final Good Neighbor Plan. However, Minnesota Power and a coalition of other Minnesota utilities and industry (the parties) co-filed challenges to the EPA’s final Minnesota SIP disapproval, submitting a petition for reconsideration and stay to the EPA, and a petition for judicial review to the U.S. Court of Appeals for the Eighth Circuit (Eighth Circuit Court). The parties are challenging and requesting reconsideration of certain technical components of the EPA’s review and subsequent partial disapproval of Minnesota’s SIP. On July 5, 2023, the Eighth Circuit Court granted the stay preventing the Good Neighbor Plan from taking effect in Minnesota.

On September 29, 2023, the EPA issued an updated final interim rule addressing the stays in Minnesota and five other states, formally delaying the effective date of the final FIP for states with active stays in place. The state of Minnesota was therefore not subject to compliance obligations for the 2023 ozone season. Future compliance obligations will depend on resolution of the stay. Additionally, challenges have been filed against the final FIP rule by the Minnesota coalition parties and other entities, although the Minnesota coalition FIP challenge is currently in abeyance pending resolution of the SIP disapproval case. In February 2024, the U.S. Supreme Court will hear arguments from several states and industry groups requesting a national stay of the FIP rule. Anticipated compliance costs related to final Good Neighbor Plan compliance cannot yet be estimated due to uncertainties about SIP approval resolution, implementation timing, FIP rule outcome, and allowance costs and facility emissions during the ozone season. However, the costs could be material, including costs of additional NOx controls, emission allowance program participation, or operational changes, if any are required. Minnesota Power would seek recovery of additional costs through a rate proceeding.

EPA National Emission Standards for Hazardous Air Pollutants for Major Sources: Industrial, Commercial and Institutional Boilers and Process Heaters (Industrial Boiler MACT) Rule. A final rule issued by the EPA for Industrial Boiler MACT became effective in 2013 with compliance required at major existing sources in 2016, which applied to Minnesota Power’s Hibbard Renewable Energy Center and Rapids Energy Center. Compliance consisted largely of adjustments to fuels and operating practices and compliance costs were not material. After this initial rulemaking, litigation from 2016 through 2018 resulted in court orders directing that the EPA reconsider certain aspects of the regulation. A final rule incorporating these revisions became effective in December 2022, with a compliance deadline of October 6, 2025. Compliance costs are not expected to be material.

EPA Mercury and Air Toxics Standards (MATS) Rule. On April 24, 2023, the EPA published a proposed revision to the existing MATS Rule as part of its mandatory 2020 MATS review. In this proposed rule, the EPA is proposing to alter certain compliance and operational requirements, and to lower several emission limits. Compliance would be required in the 2026 to 2027 timeframe. The EPA expects to issue the final rule in April 2024. The MATS regulation applies at Minnesota Power’s Boswell Energy Center, which is currently well-controlled for these emissions and is in full compliance with existing requirements. Compliance costs cannot yet be estimated; however, recovery of any additional costs would be sought through a rate proceeding.

NOTE 9. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued)

Environmental Matters (Continued)

Climate Change. The scientific community generally accepts that emissions of GHGs are linked to global climate change which creates physical and financial risks. Physical risks could include but are not limited to: increased or decreased precipitation and water levels in lakes and rivers; increased or other changes in temperatures; increased risk of wildfires; and changes in the intensity and frequency of extreme weather events. These all have the potential to affect the Company’s business and operations. We are addressing climate change by taking the following steps that also ensure reliable and environmentally compliant generation resources to meet our customers’ requirements:

•Expanding renewable power supply for both our operations and the operations of others;

•Providing energy conservation initiatives for our customers and engaging in other demand side management efforts;

•Improving efficiency of our generating facilities;

•Supporting research of technologies to reduce carbon emissions from generating facilities and carbon sequestration efforts;

•Evaluating and developing less carbon intensive future generating assets such as efficient and flexible natural gas fired generating facilities;

•Managing vegetation on right-of-way corridors to reduce potential wildfire or storm damage risks; and

•Practicing sound forestry management in our service territories to create landscapes more resilient to disruption from climate-related changes, including planting and managing long-lived conifer species.

EPA Regulation of GHG Emissions. On May 23, 2023, the EPA published in the Federal Register proposed regulatory actions under Section 111 of the Clean Air Act (CAA) addressing greenhouse gas (GHG) emissions from fossil fuel-fired electric generating units (EGUs). The EPA is proposing to revise new source performance standards (NSPS) for new, modified and reconstructed EGUs (Section 111(b) of the CAA) as well as emission guidelines for certain existing (Section 111(d) of the CAA) EGUs. The EPA is also proposing in this action to officially repeal the predecessor regulation “Affordable Clean Energy Rule”, first issued in 2019 and later vacated in 2021. The EPA’s Fall 2023 unified agenda identifies the EPA’s goal of issuing final regulations in April 2024. The Company will continue to monitor this GHG rulemaking and analyze potential impacts to existing and proposed thermal generating facilities. The rule would apply to several Company assets including existing EGUs at Boswell and Laskin as well as the proposed combined cycle natural gas-fired generating facility, NTEC. Minnesota Power continues implementing its EnergyForward strategic plan that provides for significant emissions reductions and diversifying its electricity generation mix to include more renewable and natural gas energy. We are unable to predict compliance costs due to the draft status of the rules and the need for a state implementation plan for Section 111(d) existing units; however, the costs could be material. Minnesota Power would seek recovery of additional costs through a rate proceeding.

Water. The Clean Water Act requires NPDES permits be obtained from the EPA or delegated state agency for any wastewater discharged to navigable waters. Minnesota Power has obtained all necessary NPDES permits, including NPDES storm water permits, for applicable facilities to conduct operations.

Steam Electric Power Generating Effluent Limitations Guidelines. In 2015, the EPA issued revised federal Effluent Limitation Guidelines (ELG) for steam electric power generating stations under the Clean Water Act. The ELG set effluent limits and prescribed best available control technology for several wastewater streams, including flue gas desulphurization (FGD) water, bottom ash transport water (BATW) and coal combustion landfill leachate. On October 13, 2020, the EPA published a final ELG Rule allowing re-use of bottom ash transport water in FGD scrubber systems and limited discharge for maintaining system water balance. The rule set technology standards and numerical pollutant limits for discharges of BATW and FGD wastewater. Compliance deadlines depend on subcategory, with compliance generally required as soon as possible, beginning after October 13, 2021, but no later than December 31, 2025, or December 31, 2028, in some specific cases.

On March 29, 2023, the EPA published a proposed new ELG rule in the Federal Register to update the 2020 ELGs. In the proposed rule, the EPA is revising ELGs for existing sources, including establishing zero discharge limitations for BATW and FGD wastewater; new limits for combustion residual leachate; and allowing states to set discharge limits for legacy wastewater in surface impoundments. The rule proposes to maintain exemptions for units permanently ceasing coal combustion by 2028 and adds a new subcategory for units that have already complied with either the 2015 or 2020 ELG rules and which will retire by 2032. The EPA plans to publish a final ELG rule in April 2024.

NOTE 9. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued)

Environmental Matters (Continued)

ELG revisions are not expected to have a significant impact on Minnesota Power operations. Boswell, where these ELGs are applicable, completed conversion to dry bottom ash handling and installed a FGD dewatering system in September 2022. The dry conversion projects eliminated bottom ash transport water and minimized wastewater from the FGD system. Re-use and onsite consumption are planned for the remaining BATW and FGD waste stream and for dewatering legacy wastewater from Boswell’s existing impoundments. The EPA’s reconsideration of legacy wastewater and leachate discharge requirements has the potential to impact dewatering associated with the closed impoundment at Laskin and the closed Taconite Harbor dry ash landfill.

At this time, we estimate no additional material compliance costs for ELG, BATW and FGD requirements. Compliance costs we might incur related to other ELG waste streams (e.g., leachate) or other potential future water discharge regulations at Minnesota Power facilities cannot be estimated; however, the costs could be material, including costs associated with wastewater treatment and re-use. Minnesota Power would seek recovery of additional costs through a rate proceeding.

Permitted Water Discharges – Sulfate. In 2017, the MPCA released a draft water quality standard in an attempt to update Minnesota’s existing 10 mg/L sulfate limit for waters used for the production of wild rice with the proposed rulemaking heard before an administrative law judge (ALJ). In 2018, the ALJ rejected significant portions of the proposed rulemaking and the MPCA subsequently withdrew the rulemaking. The existing 10 mg/L limit remains in place, but the MPCA is currently prohibited under state law from listing wild rice waters as impaired or requiring sulfate reduction technology.

The federal Clean Water Act requires the MPCA to update the state's impaired water list every two years. Beginning in 2021 through the latest draft proposed on November 14, 2023, this list now includes Minnesota lakes and streams identified as wild rice waters that are listed for sulfate impairment. The list could subsequently be used to set sulfate limits in discharge permits for power generation facilities and municipal and industrial customers, including paper and pulp facilities, and mining operations. At this time, we are unable to determine the specific impacts these developments may have on Minnesota Power operations or its customers, if any. Minnesota Power would seek recovery of additional costs through a rate proceeding.

Solid and Hazardous Waste. The Resource Conservation and Recovery Act (RCRA) regulates the management and disposal of solid and hazardous wastes. Minnesota Power is required to notify the EPA of hazardous waste activity and routinely submit reports to the EPA.

Coal Ash Management Facilities. Minnesota Power produces the majority of its coal ash at Boswell, with small amounts of ash generated at Hibbard Renewable Energy Center. Ash storage and disposal methods include storing ash in clay-lined onsite impoundments (ash ponds), disposing of dry ash in a lined dry ash landfill, applying ash to land as an approved beneficial use, and trucking ash to state permitted landfills.

Coal Combustion Residuals from Electric Utilities (CCR). In 2015, the EPA published a final rule (2015 Rule) regulating CCR as nonhazardous waste under Subtitle D of the Resource Conservation and Recovery Act (RCRA) in the Federal Register. The rule included requirements for new landfill and impoundment construction as well as closure activities related to certain existing impoundments. Costs of compliance for Boswell and Laskin are expected to be incurred primarily over the next 12 years and be between approximately $65 million and $120 million. Compliance costs for CCR at Taconite Harbor are not expected to be material. Minnesota Power would seek recovery of additional costs through a rate proceeding.

Minnesota Power continues to work on minimizing compliance costs through evaluation of beneficial re-use and recycling of CCR. In 2018, a U.S. District Court for the District of Columbia decision vacated specific provisions of the CCR rule, which resulted in a change to the status of several existing clay-lined impoundments at Boswell being considered unlined. In September 2020, the EPA finalized the CCR Part A Rule, which required all unlined impoundments to cease disposal and initiate closure. Upon completion of dry ash conversion activities, Boswell ceased disposal in both impoundments in September 2022. Both impoundments are now inactive and have initiated closure.

NOTE 9. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued)

Environmental Matters (Continued)

On May 17, 2023, the EPA released a proposed rule for CCR legacy surface impoundments. The proposal expands the scope of units regulated under the CCR rule to include legacy ponds (inactive surface impoundments at inactive facilities) and creates a new category of units called CCR management units, which includes inactive and closed impoundments and landfills as well as other non-containerized accumulations of CCR. The proposed rule was published in the Federal Register on May 18, 2023. The EPA is proposing to require that generating facilities evaluate and identify all past deposits of CCR materials on their sites and close or re-close existing CCR units to meet current closure standards, as well as install groundwater monitoring systems, conduct groundwater monitoring, and implement groundwater corrective actions as necessary. A final rule is expected in April 2024. This rule has the potential to impact Boswell and Laskin. Compliance costs for Minnesota Power facilities cannot be estimated at this time; however, the costs could be material. Minnesota Power would seek recovery of additional costs through a rate proceeding.

Additionally, the EPA released a proposed CCR Part B rulemaking in February 2020 addressing options for beneficial reuse of CCR materials. The final Part B rule expected in late 2024. The final CCR federal permit rule is expected in the first half of 2026. The final federal permit rule will finalize procedures for implementing a CCR federal permit program.

Other Environmental Matters

Manufactured Gas Plant Site. We are reviewing and addressing environmental conditions at a former manufactured gas plant site located in Superior, Wisconsin, and formerly operated by SWL&P. SWL&P has been working with the Wisconsin Department of Natural Resources (WDNR) in determining the extent and location of contamination at the site and surrounding properties. As of December 31, 2023, we have recorded a liability of $1 million for remediation costs at this site. SWL&P has recorded remediation costs for the site as an associated regulatory asset as we expect recovery of these remediation costs to be allowed by the PSCW.

Other Matters

We have multiple credit facility agreements in place that provide the ability to issue standby letters of credit to satisfy our contractual security requirements across our businesses. As of December 31, 2023, we had $149.8 million of outstanding letters of credit issued, including those issued under our revolving credit facility. We do not believe it is likely that any of these outstanding letters of credit will be drawn upon.

Regulated Operations. As of December 31, 2023, we had $24.2 million outstanding in standby letters of credit at our Regulated Operations which are pledged as security to MISO, the NDPSC and a state agency.

ALLETE Clean Energy. ALLETE Clean Energy is party to PSAs that expire in various years between 2024 and 2039. As of December 31, 2023, ALLETE Clean Energy has $91.6 million outstanding in standby letters of credit, the majority of which are pledged as security under these PSAs.

Corporate and Other.

BNI Energy. As of December 31, 2023, BNI Energy had surety bonds outstanding of $82.4 million related to the reclamation liability for closing costs associated with its mine and mine facilities. Although its coal supply agreements obligate the customers to provide for the closing costs, additional assurance is required by federal and state regulations. BNI Energy’s total reclamation liability is currently estimated at $82.1 million. BNI Energy does not believe it is likely that any of these outstanding surety bonds will be drawn upon.

Investment in Nobles 2. Nobles 2 wind energy facility requires standby letters of credit as security for certain contractual obligations. As of December 31, 2023, ALLETE South Wind has $10.1 million outstanding in standby letters of credit, related to our portion of the security requirements relative to our ownership in Nobles 2.

NOTE 9. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued)

Other Matters (Continued)

South Shore Energy. As of December 31, 2023, South Shore Energy had $23.9 million outstanding in standby letters of credit pledged as security in connection with the development of NTEC.

ALLETE Properties. As of December 31, 2023, ALLETE Properties had surety bonds outstanding to governmental entities totaling $2.0 million primarily related to development and maintenance obligations for various projects. The estimated cost of the remaining development work is $1.0 million. ALLETE Properties does not believe it is likely that any of these outstanding surety bonds will be drawn upon.

Community Development District Obligations. In 2005, the Town Center District issued $26.4 million of tax-exempt, 6.0 percent capital improvement revenue bonds. The capital improvement revenue bonds are payable over 31 years (by May 1, 2036) and are secured by special assessments on the benefited land. To the extent that ALLETE Properties still owns land at the time of the assessment, it will incur the cost of its portion of these assessments, based upon its ownership of benefited property.

As of December 31, 2023, we owned 33 percent of the assessable land in the Town Center District (42 percent as of December 31, 2022). As of December 31, 2023, ownership levels, our annual assessments related to capital improvement and special assessment bonds for the ALLETE Properties project within the district is approximately $0.7 million. As we sell property at this project, the obligation to pay special assessments will pass to the new landowners. In accordance with accounting guidance, these bonds are not reflected as debt on our Consolidated Balance Sheet.

Legal Proceedings.

We are involved in litigation arising in the normal course of business. Also in the normal course of business, we are involved in tax, regulatory and other governmental audits, inspections, investigations and other proceedings that involve state and federal taxes, safety, and compliance with regulations, rate base and cost of service issues, among other things. We do not expect the outcome of these matters to have a material effect on our financial position, results of operations or cash flows.

In the first quarter of 2023, an ALLETE Clean Energy subsidiary initiated arbitration proceedings seeking damages against a counterparty for non-performance under a contract. Arbitration hearings were held in June and July 2023, and a final arbitration ruling was issued in favor of ALLETE Clean Energy’s subsidiary in September 2023. The final arbitration ruling awarded $68.3 million to ALLETE Clean Energy’s subsidiary, which included prejudgment interest of $5.1 million, recovery of $3.6 million of arbitration-related costs, and resulted in the recognition of a $58.4 million pre-tax gain in the third quarter of 2023. The arbitration ruling also resulted in the receipt of approximately $60 million of cash, net of distribution to non-controlling interest, in the third quarter of 2023.

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Dec. 31, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Pension and Other Postretirement Benefit Plans - Narrative (Details) - USD ($)		12 Months Ended
	Jan. 12, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
ESOP compensation expense		$ 13,700,000	$ 12,000,000	$ 11,500,000
Subsequent Event
Defined Benefit Plan Disclosure [Line Items]
Employer contribution	$ 25,000,000
Pension
Defined Benefit Plan Disclosure [Line Items]
Employer contributions to defined benefit pension plans - cash		17,300,000	0	10,300,000
Employer contribution		26,200,000	12,300,000
Expected employer contributions in 2024		2,000,000
Net loss		256,900,000	260,200,000
Prior Service Credit		$ 0	$ 100,000
ALLETE common stock included in pension plan equity securities (in shares)		0	0
Postretirement Health and Life
Defined Benefit Plan Disclosure [Line Items]
Employer contribution			$ 300,000
Expected employer contributions in 2024		$ 0
Net loss		(24,800,000)	(9,200,000)
Prior Service Credit		(33,800,000)	(13,200,000)
Postretirement Health and Life \| VEBA
Defined Benefit Plan Disclosure [Line Items]
Employer contributions to other postretirement benefit plans		0	0	0
Postretirement Health and Life \| Irrevocable Grantor Trust
Defined Benefit Plan Disclosure [Line Items]
Employer contributions to other postretirement benefit plans		0	0	$ 0
Long-term investments		$ 12,800,000	$ 11,800,000

Fair Value - Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Fair Value of Financial Instruments [Line Items]
Short-term and long-term debt - carrying amount	$ 1,799.4	$ 1,929.1
Level 2
Fair Value of Financial Instruments [Line Items]
Short-term and long-term debt - fair value	$ 1,670.6	$ 1,782.7

Business Segments

12 Months Ended

Dec. 31, 2023

Segment Reporting [Abstract]

Business Segments

BUSINESS SEGMENTS

We present two reportable segments: Regulated Operations and ALLETE Clean Energy. We measure performance of our operations through budgeting and monitoring of contributions to consolidated net income by each business segment.

Regulated Operations includes three operating segments which consist of our regulated utilities, Minnesota Power and SWL&P, as well as our investment in ATC. ALLETE Clean Energy is our business focused on developing, acquiring and operating clean and renewable energy projects. We also present Corporate and Other which includes three operating segments, New Energy, a renewable energy development company, BNI Energy, our coal mining operations in North Dakota, and ALLETE Properties, our legacy Florida real estate investment, along with our investment in Nobles 2, South Shore Energy, our non-rate regulated, Wisconsin subsidiary developing NTEC, other business development and corporate expenditures, unallocated interest expense, a small amount of non-rate base generation, land holdings in Minnesota, and earnings on cash and investments.

NOTE 14. BUSINESS SEGMENTS (Continued)


Year Ended December 31	2023	2022	2021
Millions
Operating Revenue
Residential	$165.7	$175.9	$160.8
Commercial	184.6	187.2	168.6
Municipal	33.4	40.2	52.0
Industrial	593.6	589.0	565.5
Other Power Suppliers	146.1	165.8	168.7

Other	114.9	101.2	112.3
Total Regulated Operations	1,238.3	1,259.3	1,227.9



ALLETE Clean Energy
Long-term PSA	65.0	77.2	75.5
Sale of Wind Energy Facilities	348.4	33.5	—
Other	5.1	7.6	11.4
Total ALLETE Clean Energy	418.5	118.3	86.9

Corporate and Other
Long-term Contract	101.2	89.2	84.4
Sale of Renewable Development Projects	92.5	73.9	—
Other	29.3	30.0	20.0
Total Corporate and Other	223.0	193.1	104.4
Total Operating Revenue	$1,879.8	$1,570.7	$1,419.2
Net Income Attributable to ALLETE (a)
Regulated Operations	$147.2	$149.9	$129.1


ALLETE Clean Energy (b)	71.7	16.3	26.3


Corporate and Other (c)(d)	28.2	23.1	13.8
Total Net Income Attributable to ALLETE	$247.1	$189.3	$169.2

(a) Includes interest expense and interest income resulting from intercompany loan agreements and allocated to certain subsidiaries. The amounts are eliminated in consolidation.

(b) Net income in 2023 includes a $44.3 million after-tax gain recognized for a favorable arbitration ruling. (See Note 9. Commitments, Guarantees and Contingencies.)

(c) Net Income in 2022 includes a $8.3 million after-tax expense as a result of purchase price accounting related to projects under development at the time of acquisition and $2.7 million after-tax of transaction costs related to the acquisition of New Energy.

(d) In 2021, South Shore Energy sold a portion of its undivided ownership interest in NTEC to Basin. The closing of the transaction resulted in the recognition of an approximately $8.5 million after-tax gain which is reflected in Corporate and Other. (See Note 1. Operations and Significant Accounting Policies.)

NOTE 14. BUSINESS SEGMENTS (Continued)


Year Ended December 31	2023	2022	2021
Millions
Depreciation and Amortization
Regulated Operations	$179.2	$171.9	$170.7


ALLETE Clean Energy	57.5	58.6	49.2

Corporate and Other	15.1	11.7	11.8
Total Depreciation and Amortization	$251.8	$242.2	$231.7




Interest Expense (a)
Regulated Operations	$63.9	$58.1	$57.3


ALLETE Clean Energy	0.8	2.3	1.5

Corporate and Other	22.5	19.6	13.2

Eliminations	(6.4)	(4.8)	(2.9)
Total Interest Expense	$80.8	$75.2	$69.1
Equity Earnings
Regulated Operations	$23.1	$19.3	$21.3
Corporate and Other	(1.4)	(0.6)	(1.3)
Total Equity Earnings	$21.7	$18.7	$20.0
Income Tax Expense (Benefit)
Regulated Operations	$22.4	$(10.4)	$(16.6)


ALLETE Clean Energy	2.7	(15.4)	(16.6)

Corporate and Other	2.8	(5.4)	6.3
Total Income Tax Expense (Benefit)	$27.9	$(31.2)	$(26.9)

(a) Includes interest expense resulting from intercompany loan agreements and allocated to certain subsidiaries. The amounts are eliminated in consolidation.


As of December 31	2023	2022
Millions
Assets
Regulated Operations	$4,335.0	$4,291.4


ALLETE Clean Energy	1,594.1	1,873.3


Corporate and Other	727.3	680.9
Total Assets	$6,656.4	$6,845.6
Capital Expenditures
Regulated Operations	$236.3	$158.3


ALLETE Clean Energy	(5.3)	2.2


Corporate and Other	25.0	47.6
Total Capital Expenditures	$256.0	$208.1

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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-Name Accounting Standards Codification
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-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-15

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-31

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-42

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-40

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-26

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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-Name Accounting Standards Codification
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-Paragraph 34
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-34

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-41

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-21

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

+ Details

Commitments, Guarantees and Contingencies - Other Matters (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2023	Dec. 31, 2005	Dec. 31, 2022
Guarantor Obligations [Line Items]
Proceeds from legal settlements, gross	$ 68.3
Litigation settlement, amount awarded from other party, prejudgment interest	5.1
Litigation settlement, amount awarded from other party, arbitration costs recovery	3.6
Litigation settlement, amount awarded from other party, pre tax gain	58.4
Proceeds from legal settlements	$ 60.0
ALLETE, Inc. \| Letters of Credit
Guarantor Obligations [Line Items]
Standby letters of credit		$ 149.8
Regulated Operations \| Letters of Credit
Guarantor Obligations [Line Items]
Standby letters of credit		24.2
ALLETE Clean Energy \| Letters of Credit
Guarantor Obligations [Line Items]
Standby letters of credit		91.6
BNI Energy Reclamation Liability
Guarantor Obligations [Line Items]
Estimated obligation		82.1
BNI Energy Reclamation Liability \| Surety Bonds
Guarantor Obligations [Line Items]
Collateral		82.4
ALLETE South Wind \| Letters of Credit
Guarantor Obligations [Line Items]
Standby letters of credit		10.1
South Shore Energy \| Letters of Credit
Guarantor Obligations [Line Items]
Standby letters of credit		23.9
ALLETE Properties Development and Maintenance Obligations
Guarantor Obligations [Line Items]
Estimated obligation		1.0
ALLETE Properties Development and Maintenance Obligations \| Surety Bonds and Letters of Credit
Guarantor Obligations [Line Items]
Collateral		$ 2.0
Town Center District Capital Improvement Bonds
Guarantor Obligations [Line Items]
Bonds			$ 26.4
Bond interest rate			6.00%
Bond term			31 years
Ownership percentage of benefited property		33.00%		42.00%
Annual assessment		$ 0.7

Fair Value

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair Value

FAIR VALUE

Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). We utilize market data or assumptions that market participants would use in pricing the asset or liability, including assumptions about risk and the risks inherent in the inputs to the valuation technique. These inputs can be readily observable, market corroborated, or generally unobservable. We primarily apply the market approach for recurring fair value measurements and endeavor to utilize the best available information. Accordingly, we utilize valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. These inputs, which are used to measure fair value, are prioritized through the fair value hierarchy. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurement) and the lowest priority to unobservable inputs (Level 3 measurement). The three levels of the fair value hierarchy are as follows:

Level 1 — Quoted prices are available in active markets for identical assets or liabilities as of the reported date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis. This category includes primarily equity securities.

Level 2 — Pricing inputs are other than quoted prices in active markets, but are either directly or indirectly observable as of the reported date. The types of assets and liabilities included in Level 2 are typically either comparable to actively traded securities or contracts, such as treasury securities with pricing interpolated from recent trades of similar securities, or priced with models using highly observable inputs, such as commodity options priced using observable forward prices and volatilities. This category includes deferred compensation and fixed income securities.

Level 3 — Significant inputs that are generally less observable from objective sources. The types of assets and liabilities included in Level 3 are those with inputs requiring significant management judgment or estimation, such as the complex and subjective models and forecasts used to determine the fair value.

NOTE 7. FAIR VALUE (Continued)

The following tables set forth by level within the fair value hierarchy, our assets and liabilities that were accounted for at fair value on a recurring basis as of December 31, 2023, and December 31, 2022. Each asset and liability is classified based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement requires judgment, which may affect the valuation of these assets and liabilities and their placement within the fair value hierarchy levels. The estimated fair value of Cash and Cash Equivalents listed on the Consolidated Balance Sheet approximates the carrying amount and therefore is excluded from the recurring fair value measures in the following tables.


	Fair Value as of December 31, 2023
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets:
Investments (a)
Available-for-sale – Equity Securities	$8.7	—	—	$8.7
Available-for-sale – Corporate and Governmental Debt Securities (b)	—	$6.0	—	6.0
Cash Equivalents	5.8	—	—	5.8
Total Fair Value of Assets	$14.5	$6.0	—	$20.5

Liabilities:
Deferred Compensation (c)	—	$16.5	—	$16.5

Total Fair Value of Liabilities	—	$16.5	—	$16.5

(a)Included in Other Non-Current Assets on the Consolidated Balance Sheet.

(c)Included in Other Non-Current Liabilities on the Consolidated Balance Sheet.


	Fair Value as of December 31, 2022
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets:
Investments (a)
Available-for-sale – Equity Securities	$7.7	—	—	$7.7
Available-for-sale – Corporate and Governmental Debt Securities	—	$5.7	—	5.7
Cash Equivalents	4.2	—	—	4.2
Total Fair Value of Assets	$11.9	$5.7	—	$17.6

Liabilities: (b)
Deferred Compensation	—	$15.0	—	$15.0

Total Fair Value of Liabilities	—	$15.0	—	$15.0

(a)Included in Other Non-Current Assets on the Consolidated Balance Sheet.

(b)Included in Other Non-Current Liabilities on the Consolidated Balance Sheet.

The Company’s policy is to recognize transfers in and transfers out of levels as of the actual date of the event or change in circumstances that caused the transfer. For the years ended December 31, 2023 and 2022, there were no transfers in or out of Levels 1, 2 or 3.

Fair Value of Financial Instruments. With the exception of the item listed in the following table, the estimated fair value of all financial instruments approximates the carrying amount. The fair value for the item listed in the following table was based on quoted market prices for the same or similar instruments (Level 2).

NOTE 7. FAIR VALUE (Continued)


Financial Instruments	Carrying Amount	Fair Value
Millions
Short-Term and Long-Term Debt (a)
December 31, 2023	$1,799.4	$1,670.6
December 31, 2022	$1,929.1	$1,782.7

(a) Excludes unamortized debt issuance costs.

Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis. Non-financial assets such as equity method investments, goodwill, intangible assets, and property, plant and equipment are measured at fair value when there is an indicator of impairment and recorded at fair value only when an impairment is recognized.

Equity Method Investments. The aggregate carrying amount of our equity investments was $331.2 million as of December 31, 2023 ($322.7 million as of December 31, 2022). The Company assesses our equity investments in ATC and Nobles 2 for impairment whenever events or changes in circumstances indicate that the carrying amount of our investments may not be recoverable. For the years ended December 31, 2023 and 2022, there were no indicators of impairment. (See Note 6. Equity Investments.)

Goodwill. The Company assesses the impairment of goodwill annually in the fourth quarter and whenever an event occurs or circumstances change that would indicate that the carrying amount may be impaired. The Company’s goodwill is a result of the New Energy acquisition in 2022. (See Note 1. Operations and Significant Accounting Policies and Note 5. Acquisitions.) The aggregate carrying amount of goodwill was $154.9 million as of December 31, 2023.

Property, Plant and Equipment. The Company assesses the impairment of property, plant, and equipment whenever events or changes in circumstances indicate that the carrying amount of property, plant, and equipment assets may not be recoverable. (See Note 1. Operations and Significant Accounting Policies.) For the years ended December 31, 2023, and 2022, there was no impairment of property, plant, and equipment.

We believe that long-standing ratemaking practices approved by applicable state and federal regulatory commissions allow for the recovery of the remaining book value of retired plant assets. The MPUC order for Minnesota Power’s 2015 IRP directed Minnesota Power to retire Boswell Units 1 and 2, which occurred in the fourth quarter of 2018. As part of the 2016 general retail rate case, the MPUC allowed recovery of the remaining book value of Boswell Units 1 and 2 through 2022. Minnesota Power’s latest IRP, which was approved by the MPUC in an order dated January 9, 2023, includes ceasing coal operations at Boswell Units 3 and 4 by 2030 and 2035, respectively. Boswell Unit 3 and Unit 4 have a net book value of approximately $220 million and $420 million, respectively, as of December 31, 2023. (See Note 4. Regulatory Matters.) Minnesota Power also retired Taconite Harbor in the first quarter of 2023 consistent with its latest IRP. As part of the 2022 general retail rate case, the MPUC allowed recovery of the remaining book value of Taconite Harbor through 2026. We do not expect to record any impairment charge as a result of these operating changes at Taconite Harbor and Boswell. In addition, we expect to be able to continue depreciating these assets for at least their established remaining useful lives; however, we are unable to predict the impact of regulatory outcomes resulting in changes to their established remaining useful lives.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Pension and Other Postretirement Benefit Plans - Information for Pension Plans with an Accumulated Benefit Obligation in Excess of Plan Assets (Details) - Pension - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Projected Benefit Obligation	$ 746.3	$ 739.7
Accumulated Benefit Obligation	729.5	724.5
Fair Value of Plan Assets	$ 589.0	$ 568.6

Employee Stock and Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Share-Based Compensation Expense

The following share-based compensation expense amounts were recognized in our Consolidated Statement of Income for the periods presented.


Share-Based Compensation Expense
Year Ended December 31	2023	2022	2021
Millions

Performance Shares	$3.1	$0.7	$2.0
Restricted Stock Units	0.8	0.9	1.0
Total Share-Based Compensation Expense	$3.9	$1.6	$3.0
Income Tax Benefit	$1.1	$0.5	$0.9

Performance Shares

Performance Shares. The following table presents information regarding our non-vested performance shares.


	2023		2022		2021
	Number of Shares	Weighted- Average Grant Date Fair Value	Number of Shares	Weighted- Average Grant Date Fair Value	Number of Shares	Weighted- Average Grant Date Fair Value
Non-vested as of January 1	60,489	$69.62	80,661	$75.80	85,284	$80.73
Granted (a)	54,039	$63.50	37,731	$67.22	33,304	$73.25
Awarded	—	—	—	—	—	—
Unearned Grant Award	—	—	(50,524)	$77.49	(33,375)	$86.09
Forfeited	(3,030)	$67.60	(7,379)	$71.00	(4,552)	$74.05
Non-vested as of December 31	111,498	$66.71	60,489	$69.62	80,661	$75.80

(a) Shares granted include accrued dividends.

Restricted Stock Units

Restricted Stock Units. The following table presents information regarding our available restricted stock units.


	2023		2022		2021
	Number of Shares	Weighted- Average Grant Date Fair Value	Number of Shares	Weighted- Average Grant Date Fair Value	Number of Shares	Weighted- Average Grant Date Fair Value
Available as of January 1	33,564	$68.80	28,141	$73.16	37,482	$77.64
Granted (a)	21,200	$61.16	15,477	$63.70	16,251	$64.97
Awarded	(9,631)	$81.91	(7,396)	$75.55	(23,631)	$74.53
Forfeited	(1,389)	$63.46	(2,658)	$66.44	(1,961)	$74.52
Available as of December 31	43,744	$62.38	33,564	$68.80	28,141	$73.16

(a) Shares granted include accrued dividends.

Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Comprehensive Income [Abstract]
Net Income	$ 178.9	$ 131.3	$ 137.8
Other Comprehensive Income (Loss)
Net of Income Tax Expense (Benefit) of $0.1, $(0.2) and $(0.1)	0.3	(0.4)	(0.1)
Net of Income Tax Expense (Benefit) of $2.4, $(0.1) and $3.0	3.6	(0.2)	7.4
Total Other Comprehensive Income (Loss)	3.9	(0.6)	7.3
Total Comprehensive Income	182.8	130.7	145.1
Net Loss Attributable to Non-Controlling Interest	(68.2)	(58.0)	(31.4)
Total Comprehensive Income Attributable to ALLETE	$ 251.0	$ 188.7	$ 176.5

- Definition

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income (loss) and other comprehensive income (loss), attributable to noncontrolling interests. Excludes changes in equity resulting from investments by owners and distributions to owners.

+ References + Details

- Definition

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income. Excludes changes in equity resulting from investments by owners and distributions to owners.

+ References + Details

- Definition

Amount after tax and reclassification adjustments of other comprehensive income (loss).

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The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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+ Details

Consolidated Statement of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Revenue [Abstract]
Contracts with Customers – Utility	$ 1,238.3	$ 1,259.3	$ 1,227.9
Contracts with Customers – Non-utility	636.4	303.8	179.9
Other – Non-utility	5.1	7.6	11.4
Total Operating Revenue	1,879.8	1,570.7	1,419.2
Operating Expenses
Fuel, Purchased Power and Gas – Utility	482.9	545.5	562.4
Transmission Services – Utility	88.2	76.7	75.3
Cost of Sales – Non-utility	473.5	182.8	68.8
Operating and Maintenance	345.3	318.9	259.2
Depreciation and Amortization	251.8	242.2	231.7
Taxes Other than Income Taxes	57.2	70.4	70.5
Total Operating Expenses	1,698.9	1,436.5	1,267.9
Operating Income	180.9	134.2	151.3
Other Income (Expense)
Interest Expense	(80.8)	(75.2)	(69.1)
Equity Earnings	21.7	18.7	20.0
Other	85.0	22.4	8.7
Total Other Income (Expense)	25.9	(34.1)	(40.4)
Income Before Non-Controlling Interest and Income Taxes	206.8	100.1	110.9
Income Tax Expense (Benefit)	27.9	(31.2)	(26.9)
Net Income	178.9	131.3	137.8
Net Loss Attributable to Non-Controlling Interest	(68.2)	(58.0)	(31.4)
Net Income Attributable to ALLETE	$ 247.1	$ 189.3	$ 169.2
Average Shares of Common Stock
Basic (in shares)	57.3	55.9	52.4
Diluted (in shares)	57.4	56.0	52.5
Basic Earnings Per Share of Common Stock (in usd per share)	$ 4.31	$ 3.38	$ 3.23
Diluted Earnings Per Share of Common Stock (in dollars per share)	$ 4.30	$ 3.38	$ 3.23

Operations and Significant Accounting Policies - Lease Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Operating
2024	$ 3.2
2025	3.2
2026	3.2
2027	4.1
2028	0.2
Thereafter	1.2
Total Lease Payments Due	15.1
Less: Imputed Interest	4.4
Total Lease Obligations	10.7
Less: Current Lease Obligations	3.0	$ 3.2
Operating Lease Liabilities	7.7	9.3
Finance
2024	0.4
2025	0.4
2026	0.4
2027	0.5
2028	0.6
Thereafter	0.0
Total Lease Payments Due	2.3
Less: Imputed Interest	0.3
Total Lease Obligations	2.0
Less: Current Lease Obligations	0.4	0.0
Finance Lease Liabilities	$ 1.6	$ 0.0

Consolidated Balance Sheet - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Current Assets
Cash and Cash Equivalents	$ 71.9	$ 36.4
Accounts Receivable (Less Allowance of $1.6 and $1.6 )	137.2	137.9
Inventories – Net	175.4	455.9
Prepayments and Other	83.6	87.8
Total Current Assets	468.1	718.0
Property, Plant and Equipment – Net	5,013.4	5,004.0
Regulatory Assets	425.4	441.0
Equity Investments	331.2	322.7
Goodwill and Intangible Assets – Net	155.4	155.6
Other Non-Current Assets	262.9	204.3
Total Assets	6,656.4	6,845.6
Current Liabilities
Accounts Payable	102.2	103.0
Accrued Taxes	51.0	69.1
Accrued Interest	21.1	20.5
Long-Term Debt Due Within One Year	111.4	272.6
Other	91.9	251.0
Total Current Liabilities	377.6	716.2
Long-Term Debt	1,679.9	1,648.2
Deferred Income Taxes	192.7	158.1
Regulatory Liabilities	574.0	526.1
Defined Benefit Pension and Other Postretirement Benefit Plans	160.8	179.7
Other Non-Current Liabilities	264.3	269.0
Total Liabilities	3,249.3	3,497.3
Commitments, Guarantees and Contingencies (Note 9)
Redeemable Non-Controlling Interest	0.5	0.0
ALLETE Equity
Common Stock Without Par Value, 80.0 Shares Authorized, 57.6 and 57.2 Shares Issued and Outstanding	1,803.7	1,781.5
Accumulated Other Comprehensive Loss	(20.5)	(24.4)
Retained Earnings	1,026.4	934.8
Total ALLETE Equity	2,809.6	2,691.9
Non-Controlling Interest in Subsidiaries	597.0	656.4
Total Equity	3,406.6	3,348.3
Total Liabilities, Redeemable Non-Controlling Interest and Equity	$ 6,656.4	$ 6,845.6

Regulatory Matters

12 Months Ended

Dec. 31, 2023

Regulated Operations [Abstract]

Regulatory Matters

REGULATORY MATTERS

Electric Rates. Entities within our Regulated Operations segment file for periodic rate revisions with the MPUC, PSCW or FERC. As authorized by the MPUC, Minnesota Power also recognizes revenue under cost recovery riders for transmission, renewable and environmental investments and expenditures. (See Transmission Cost Recovery Rider, Renewable Cost Recovery Rider, Solar Cost Recovery Rider and Environmental Improvement Rider.) Revenue from cost recovery riders was $57.0 million in 2023 ($38.8 million in 2022; $38.9 million in 2021).

Minnesota Retail Rates. Minnesota Power’s retail base rates through 2021 were based on a 2018 MPUC retail rate order that allowed for a 9.25 percent return on common equity and a 53.81 percent equity ratio. Interim rates were implemented in Minnesota Power’s 2022 general rate case beginning in January 2022, and the resolution of Minnesota Power’s 2022 general rate case changed the allowed return on equity to 9.65 percent and the equity ratio to 52.50 percent beginning October 1, 2023. (See 2022 Minnesota General Rate Case.)

2024 Minnesota General Rate Case. On November 1, 2023, Minnesota Power filed a retail rate increase request with the MPUC seeking an average increase of approximately 12.00 percent for retail customers, net of rider revenue incorporated into base rates. The rate filing seeks a return on equity of 10.30 percent and a 53.00 percent equity ratio. On an annualized basis, the requested final rate increase would generate approximately $89 million in additional revenue. In orders dated December 19, 2023, the MPUC accepted the filing as complete and approved an annual interim rate increase of approximately $64 million, net of rider revenue, beginning January 1, 2024, subject to refund. We cannot predict the level of final rates that may be authorized by the MPUC.

2022 Minnesota General Rate Case. On November 1, 2021, Minnesota Power filed a retail rate increase request with the MPUC seeking an average increase of approximately 18 percent for retail customers. The rate filing sought a return on equity of 10.25 percent and a 53.81 percent equity ratio. On an annualized basis, the requested final rate increase would have generated approximately $108 million in additional revenue.

NOTE 4. REGULATORY MATTERS (Continued)

Electric Rates (Continued)

In an order dated February 28, 2023, the MPUC made determinations regarding Minnesota Power’s general rate case including allowing a return on common equity of 9.65 percent and a 52.50 percent equity ratio. We expect additional revenue from base rates of approximately $60 million and an additional $10 million in revenue recognized under cost recovery riders on an annualized basis. On March 20, 2023, Minnesota Power filed a petition for reconsideration with the MPUC requesting reconsideration and clarification of certain decisions in the MPUC’s order. Minnesota Power’s petition included requesting reconsideration of the ratemaking treatment of Taconite Harbor and Minnesota Power’s prepaid pension asset as well as clarification on interim rate treatment for sales to certain customers that did not operate during 2022. The MPUC denied the requests for reconsideration in an order dated May 15, 2023, and provided clarification in support of the interim rate refund treatment for sales to certain customers that did not operate during 2022.

On June 14, 2023, Minnesota Power appealed to the Minnesota Court of Appeals (Court) specific aspects of the MPUC’s rate case orders. Minnesota Power is appealing the ratemaking treatment of Taconite Harbor and Minnesota Power’s prepaid pension asset. We are unable to predict the outcome of this proceeding.

In an order dated September 29, 2023, the MPUC approved Minnesota Power’s final rates, which were implemented beginning on October 1, 2023. The MPUC order also approved Minnesota Power’s interim rate refund plan. Interim rates were collected through the third quarter with reserves recorded as necessary. Minnesota Power recorded a reserve for an interim rate refund of approximately $39 million pre-tax as of September 30, 2023 (approximately $18 million as of December 31, 2022), which was refunded to customers during the fourth quarter of 2023.

FERC-Approved Wholesale Rates. Minnesota Power has wholesale contracts with 14 non-affiliated municipal customers in Minnesota and SWL&P. Two of the wholesale contracts include a termination clause requiring a three-year notice to terminate.

Minnesota Power’s wholesale electric contract with the Nashwauk Public Utilities Commission is effective through December 31, 2037. The wholesale electric service contract with SWL&P is effective through February 28, 2027. Under the agreement with SWL&P, no termination notice has been given. The rates included in these two contracts are set each July 1 based on a cost-based formula methodology, using estimated costs and a rate of return that is equal to Minnesota Power’s authorized rate of return for Minnesota retail customers. The formula-based rate methodology also provides for a yearly true-up calculation for actual costs incurred.

Minnesota Power’s wholesale electric contracts with 13 other municipal customers were extended in January 2022 and are effective through 2029. These contracts are based on fixed prices for capacity and energy. The base energy charge for each year is adjusted annually for updated fuel and purchased power costs.

Transmission Cost Recovery Rider. Minnesota Power has an approved cost recovery rider in place to charge retail customers on a current basis for certain transmission investments and expenditures, including a return on the capital invested. Current customer billing rates are based on an MPUC order dated December 19, 2023, which provisionally approved Minnesota Power’s latest transmission factor filing submitted on October 24, 2023. Updated billing rates were included on customer bills starting in the first quarter of 2024.

Renewable Cost Recovery Rider. Minnesota Power has an approved cost recovery rider in place to charge retail customers on a current basis for the costs of certain renewable investments and expenditures, including a return on the capital invested. Customer billing rates for the renewable cost recovery rider had been based on a MPUC order dated January 24, 2023. On March 29, 2023, Minnesota Power submitted its latest renewable cost recovery rider factor filing, which the MPUC approved in an order dated October 3, 2023. Updated billing rates were included on customer bills starting in the fourth quarter of 2023.

Solar Cost Recovery Rider. Minnesota Power has an approved cost recovery rider in place to charge retail customers on a current basis for solar costs related to investments and expenditures for meeting the state of Minnesota’s solar energy standard. Customer billing rates for the solar cost recovery rider had been based on an August 2022 MPUC order. On August 23, 2023, Minnesota Power submitted its latest solar cost recovery rider factor filing, which the MPUC approved in an order dated December 26, 2023. Updated billing rates were included on customer bills starting in the first quarter of 2024.

Fuel Adjustment Clause. Fuel and purchased power costs related to Minnesota Power’s retail customers are recovered from customers through the fuel adjustment clause. The method of accounting for all Minnesota electric utilities is a monthly budgeted, forward-looking fuel adjustment clause with annual prudence review and true-up to actual allowed costs.

NOTE 4. REGULATORY MATTERS (Continued)

Electric Rates (Continued)

Minnesota Power incurred higher fuel and purchased power costs in 2021 than those factored in its fuel adjustment forecast filed in May 2020 for 2021, which resulted in the recognition of an approximately $56 million regulatory asset as of December 31, 2021. The MPUC approved recovery of the regulatory asset in a July 2022 order; recovery of the regulatory asset was completed in 2023.

Minnesota Power incurred higher fuel and purchased power costs in 2022 than those factored in its fuel adjustment forecast filed in May 2021 for 2022, which resulted in the recognition of an approximately $13 million regulatory asset as of December 31, 2022. The MPUC approved recovery of the regulatory asset in an order dated July 31, 2023; recovery of the regulatory asset began in the third quarter of 2023 and will continue through mid-2024.

Minnesota Power incurred lower fuel and purchased power costs in 2023 than those factored in its fuel adjustment forecast filed in May 2022 for 2023, which resulted in the recognition of a $15.5 million regulatory liability as of December 31, 2023. On August 30, 2023, Minnesota Power submitted a filing with the MPUC requesting to refund a portion of over-collected fuel adjustment clause recoveries for 2023 from October 2023 through December 2023. No parties objected to the request and lower rates were implemented in October 2023, subject to final approval by the MPUC which is expected in 2024.

In May 2023, Minnesota Power filed its fuel adjustment forecast for 2024 which was subsequently approved by the MPUC in an order dated November 9, 2023. The fuel and purchase power rates for Minnesota Power retail customers are based on this filing beginning January 1, 2024.

Wisconsin Retail Rates. SWL&P’s retail rates through 2022 were based on a December 2018 order by the PSCW that allowed for a return on equity of 10.40 percent and a 55.00 percent equity ratio. The resolution of SWL&P’s 2022 general rate case changed the allowed return on equity to 10.00 percent and maintained an equity ratio of 55.00 percent. (See 2022 Wisconsin General Rate Case.)

2022 Wisconsin General Rate Case. In 2022, SWL&P filed a rate increase request with the PSCW seeking an average increase of 3.60 percent for retail customers. The filing sought an overall return on equity of 10.40 percent and a 55.00 percent equity ratio. On an annualized basis, the requested final rate increase would have generated an estimated $4.3 million in additional revenue. In an order dated December 20, 2022, the PSCW approved an annual increase of $3.3 million reflecting a return on equity of 10.00 percent and 55.00 percent equity ratio. Final rates went into effect January 1, 2023.

Integrated Resource Plan. On February 1, 2021, Minnesota Power filed its latest IRP, which was approved by the MPUC in an order dated January 9, 2023. The approved IRP, which reflects a joint agreement reached with various stakeholders, outlines Minnesota Power’s clean-energy transition plans through 2035. These plans include expanding its renewable energy supply, achieving coal-free operations at its facilities by 2035, and investing in a resilient and flexible transmission and distribution grid. As part of these plans, Minnesota Power anticipates adding up to 700 MW of new wind and solar energy resources, and ceasing coal operations at Boswell Units 3 and 4 by 2030 and 2035, respectively. Minnesota Power’s plans recognize that advances in technology will play a significant role in completing its transition to carbon-free energy supply, reliably and affordably. Minnesota Power is expected to file its next IRP by March 1, 2025.

Solar Energy Request For Proposals. On October 2, 2023, Minnesota Power filed a notice with the MPUC of its intent to issue a request for proposals for up to 300 MW of solar energy resources. Minnesota Power issued the request for proposals on November 15, 2023, which were accepted through January 17, 2024.

Wind Energy Request For Proposals. On December 15, 2023, Minnesota Power filed a notice with the MPUC of its intent to issue a request for proposals for up to 400 MW of wind energy resources. Minnesota Power issued the request for proposals on February 15, 2024.

Energy Conservation and Optimization (ECO) Plan. Minnesota requires electric utilities to spend a minimum of 1.5 percent of gross operating revenues, excluding revenue received from exempt customers, from service provided in the state on ECOs each year. On April 3, 2023, Minnesota Power submitted its 2022 ECO, formerly known as the conservation improvement program, annual filing detailing Minnesota Power’s ECO plan results and proposed financial incentive, which was approved by the MPUC on July 21, 2023. As a result, Minnesota Power recognized revenue of $2.2 million in 2023 for the approved financial incentive ($1.9 million in 2022 and $2.4 million in 2021). The financial incentives are recognized in the period in which the MPUC approves the filing.

NOTE 4. REGULATORY MATTERS (Continued)

On June 30, 2023, Minnesota Power submitted its triennial filing for 2024 through 2026 to the MPUC and Minnesota Department of Commerce, which outlines Minnesota Power’s ECO spending and energy-saving goals for those years. Minnesota Power’s investment goals are $12.5 million for 2024, $12.7 million for 2025 and $12.8 million for 2026.

MISO Return on Equity Complaint. MISO transmission owners, including ALLETE and ATC, have an authorized return on equity of 10.02 percent, or 10.52 percent including an incentive adder for participation in a regional transmission organization based on a 2020 FERC order which is subject to various outstanding legal challenges related to the return on equity calculation and refund period ordered by the FERC. In August 2022, the U.S. Court of Appeals for the District of Columbia Circuit vacated and remanded the 2020 FERC order back to the FERC. We cannot predict the return on equity the FERC will ultimately authorize in the remanded proceeding. (See Note 6. Equity Investments.)

Minnesota Solar Energy Standard. Minnesota law requires at least 1.5 percent of total retail electric sales, excluding sales to certain customers, to be generated by solar energy. At least 10 percent of the 1.5 percent mandate must be met by solar energy generated by or procured from solar photovoltaic devices with a nameplate capacity of 40 kW or less and community solar garden subscriptions. Minnesota Power has met both parts of the solar mandate to date.

In June 2020, Minnesota Power filed a proposal with the MPUC to accelerate its plans for purchasing solar energy from approximately 20 MW of solar energy projects in Minnesota which was approved in a June 2021 order. These solar energy projects were constructed and owned through an ALLETE subsidiary with an investment of approximately $40 million. Construction of these solar energy projects commenced in 2022 with a portion of these projects placed into service in the fourth quarter of 2022; the remaining project was placed into service in 2023.

Regulatory Assets and Liabilities. Our regulated utility operations are subject to accounting standards for the effects of certain types of regulation. Regulatory assets represent incurred costs that have been deferred as they are probable for recovery in customer rates. Regulatory liabilities represent obligations to make refunds to customers and amounts collected in rates for which the related costs have not yet been incurred. The Company assesses quarterly whether regulatory assets and liabilities meet the criteria for probability of future recovery or deferral. With the exception of the regulatory asset for Boswell Units 1 and 2 net plant and equipment, no other regulatory assets are currently earning a return. The recovery, refund or credit to rates for these regulatory assets and liabilities will occur over the periods either specified by the applicable regulatory authority or over the corresponding period related to the asset or liability.

NOTE 4. REGULATORY MATTERS (Continued)


Regulatory Assets and Liabilities
As of December 31	2023	2022
Millions
Current Regulatory Assets (a)
Fuel Adjustment Clause (b)	$8.7	$25.6
Other	0.6	—
Total Current Regulatory Assets	$9.3	$25.6
Non-Current Regulatory Assets

Defined Benefit Pension and Other Postretirement Benefit Plans (c)	$218.6	$225.9

Income Taxes (d)	88.1	97.6
Asset Retirement Obligations (e)	37.7	35.6
Cost Recovery Riders (f)	33.8	41.2
Taconite Harbor (g)	20.9	—
Manufactured Gas Plant (h)	13.2	15.1
Fuel Adjustment Clause (b)	5.0	14.5
PPACA Income Tax Deferral	3.9	4.1


Other	4.2	7.0
Total Non-Current Regulatory Assets	$425.4	$441.0


Current Regulatory Liabilities (i)
Provision for Interim Rate Refund	—	$18.4


Transmission Formula Rates Refund	$1.5	4.9
Other	2.4	0.1
Total Current Regulatory Liabilities	$3.9	$23.4
Non-Current Regulatory Liabilities

Income Taxes (d)	$310.0	$332.5
Wholesale and Retail Contra AFUDC (j)	78.0	80.7
Plant Removal Obligations (k)	67.0	60.0

Defined Benefit Pension and Other Postretirement Benefit Plans (c)	48.6	17.6
Non-Jurisdictional Land Sales (l)	30.2	7.5
Fuel Adjustment Clause (b)	15.5	—
Investment Tax Credits (m)	13.6	16.9
Boswell Units 1 and 2 Net Plant and Equipment (n)	6.7	6.7


Other	4.4	4.2
Total Non-Current Regulatory Liabilities	$574.0	$526.1

(a)Current regulatory assets are presented within Prepayments and Other on the Consolidated Balance Sheet.

(b)Fuel adjustment clause regulatory assets and liabilities represent the amount expected to be recovered from or refunded to customers for the under- or over-collection of fuel adjustment clause recoveries. (See Fuel Adjustment Clause.)

(c)Defined benefit pension and other postretirement items included in our Regulated Operations, which are otherwise required to be recognized in accumulated other comprehensive income, are recognized as regulatory assets or regulatory liabilities on the Consolidated Balance Sheet. The asset or liability will decrease as the deferred items are amortized and recognized as components of net periodic benefit cost. (See Note 12. Pension and Other Postretirement Benefit Plans.)

(d)These costs represent the difference between deferred income taxes recognized for financial reporting purposes and amounts previously billed to our customers. The balances will primarily decrease over the remaining life of the related temporary differences.

(e)Asset retirement obligations will accrete and be amortized over the lives of the related property with asset retirement obligations.

(f)The cost recovery rider regulatory assets and liabilities are revenue not yet collected from our customers and cash collections from our customers in excess of the revenue recognized, respectively, primarily due to capital expenditures related to Bison and the GNTL as well as differences between production tax credits recognized and those assumed in Minnesota Power’s base rates. The cost recovery rider regulatory assets as of December 31, 2023, will be recovered within the next two years.

(g)In the first quarter of 2023, Minnesota Power retired Taconite Harbor Units 1 and 2. The remaining net book value was reclassified from property, plant and equipment to a regulatory asset on the Consolidated Balance Sheet when the units were retired. Minnesota Power expects to receive recovery of the remaining net book value from customers.

(h)This regulatory asset represents costs of remediation for a former manufactured gas plant site located in Superior, Wisconsin, and formerly operated by SWL&P. We expect recovery of these remediation costs to be allowed by the PSCW in rates over time.

(i)Current regulatory liabilities are presented within Other Current Liabilities on the Consolidated Balance Sheet.

(j)Wholesale and retail contra AFUDC represents amortization to offset AFUDC Equity and Debt recorded during the construction period of our cost recovery rider projects prior to placing the projects in service. The regulatory liability will decrease over the remaining depreciable life of the related asset.

(k)Non-legal plant removal obligations included in retail customer rates that have not yet been incurred.

(l)This regulatory liability represents the net proceeds from the sale of certain land by Minnesota Power that is expected to be refunded to ratepayers through a future rate case or through its renewable resources rider.

(m)North Dakota and Federal investment tax credits expected to be realized from Minnesota Power’s Bison facility and SWL&P’s community solar facility that will be credited to retail customers primarily through future renewable cost recovery rider as the tax credits are utilized.

(n)In 2018, Minnesota Power retired Boswell Units 1 and 2 and reclassified the remaining net book value from property, plant and equipment to a regulatory asset on the Consolidated Balance Sheet. The remaining net book value is currently included in Minnesota Power’s rate base and Minnesota Power is earning a return on the outstanding balance.

Pension and Other Postretirement Benefit Plans

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

Pension and Other Postretirement Benefit Plans

PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS

We have noncontributory union, non-union and combined retiree defined benefit pension plans covering eligible employees. The combined retiree defined benefit pension plan was created in 2016, to include all union and non-union retirees from the existing plans as of January 2016. The plans provide defined benefits based on years of service and final average pay. We made $17.3 million in cash contributions to the plan trusts in 2023 (none in 2022; $10.3 million in 2021). We also have a defined contribution RSOP covering substantially all employees. The 2023 plan year employer contributions totaled $13.7 million ($12.0 million for the 2022 plan year; $11.5 million for the 2021 plan year). (See Note 10. Common Stock and Earnings Per Share and Note 13. Employee Stock and Incentive Plans.)

The non-union defined benefit pension plan was frozen in 2018, and does not allow further crediting of service or earnings to the plan. Further, it is closed to new participants. The Minnesota Power union defined benefit pension plan is also closed to new participants, and the SWL&P union defined benefit pension plan was closed to new participants effective February 1, 2022.

We have postretirement health care and life insurance plans covering eligible employees. In 2010, the postretirement health care plan was closed to employees hired after January 2011, and the eligibility requirements were amended. The postretirement life plan was amended in 2014 to close the plan to non-union employees retiring after 2015, and in 2018, the plan was amended to limit the benefit level for union employees retiring after 2018. In 2023, the postretirement health care plan was amended to change the company contribution to an annual stipend for certain retirees. The postretirement health and life plans are contributory with participant contributions adjusted annually. Postretirement health and life benefits are funded through a combination of Voluntary Employee Benefit Association trusts (VEBAs), established under section 501(c)(9) of the Internal Revenue Code, and irrevocable grantor trusts. In 2023, no contributions were made to the VEBAs (none in 2022; none in 2021) and no contributions were made to the grantor trusts (none in 2022; none in 2021).

Management considers various factors when making funding decisions such as regulatory requirements, actuarially determined minimum contribution requirements and contributions required to avoid benefit restrictions for the pension plans. Contributions are based on estimates and assumptions which are subject to change. On January 12, 2024, we contributed $25.0 million in cash to the defined benefit pension plans, and expect to make $2.0 million in additional cash contributions to the defined benefit pension plans in 2024. We do not expect to make any contributions to the defined benefit postretirement health and life plans in 2024.

Accounting for defined benefit pension and other postretirement benefit plans requires that employers recognize on a prospective basis the funded status of their defined benefit pension and other postretirement plans on their balance sheet and recognize as a component of other comprehensive income, net of tax, the gains or losses and prior service costs or credits that arise during the period but are not recognized as components of net periodic benefit cost.

The defined benefit pension and postretirement health and life benefit expense (credit) recognized annually by our regulated utilities are expected to be recovered (refunded) through rates filed with our regulatory jurisdictions. As a result, these amounts that are required to otherwise be recognized in accumulated other comprehensive income have been recognized as a long-term regulatory asset (regulatory liability) on the Consolidated Balance Sheet, in accordance with the accounting standards for the effect of certain types of regulation applicable to our Regulated Operations. The defined benefit pension and postretirement health and life benefit expense (credits) associated with our other operations are recognized in accumulated other comprehensive income.

NOTE 12. PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Continued)


Pension Obligation and Funded Status
As of December 31	2023	2022
Millions
Accumulated Benefit Obligation	$729.5	$724.5
Change in Benefit Obligation
Obligation, Beginning of Year	$739.7	$911.7
Service Cost	6.5	9.3
Interest Cost	40.5	27.2
Plan Amendments	—	0.8

Actuarial (Gain) Loss (a)	13.9	(160.6)
Benefits Paid	(60.9)	(58.9)
Participant Contributions	6.6	10.2
Obligation, End of Year	$746.3	$739.7
Change in Plan Assets
Fair Value, Beginning of Year	$568.6	$745.7
Actual Return on Plan Assets	55.1	(130.5)
Employer Contribution (b)	26.2	12.3
Benefits Paid	(60.9)	(58.9)
Fair Value, End of Year	$589.0	$568.6
Funded Status, End of Year	$(157.3)	$(171.1)

Net Pension Amounts Recognized in Consolidated Balance Sheet Consist of:
Current Liabilities	$(2.1)	$(2.1)
Non-Current Liabilities	$(155.2)	$(169.0)

(a) Actuarial gain in 2022 was primarily the result of increases in discount rates.

(b) Includes Participant Contributions noted above, any contributions made by the Company to pension plan trusts and any direct benefit payments made under certain plans.

The pension costs that are reported as a component within the Consolidated Balance Sheet, reflected in long-term regulatory assets or liabilities and accumulated other comprehensive income, consist of a net loss of $256.9 million as of December 31, 2023 (net loss of $260.2 million and prior service credit of $0.1 million as of December 31, 2022.

NOTE 12. PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Continued)


Reconciliation of Net Pension Amounts Recognized in Consolidated Balance Sheet
As of December 31	2023	2022
Millions
Net Loss	$(256.9)	$(260.2)
Prior Service Credit	—	0.1
Accumulated Contributions in Excess of Net Periodic Benefit Cost (Prepaid Pension Asset)	99.6	89.0
Total Net Pension Amounts Recognized in Consolidated Balance Sheet	$(157.3)	$(171.1)


Components of Net Periodic Pension Cost
Year Ended December 31	2023	2022	2021
Millions
Service Cost	$6.5	$9.3	$11.0
Non-Service Cost Components (a)
Interest Cost	40.5	27.2	24.6
Expected Return on Plan Assets	(43.8)	(41.5)	(43.4)
Amortization of Loss	5.8	11.4	18.8
Amortization of Prior Service Credit	(0.1)	(0.1)	(0.2)
Net Pension Cost	$8.9	$6.3	$10.8

(a)These components of net periodic pension cost are included in the line item “Other” under Other Income (Expense) on the Consolidated Statement of Income.


Other Changes in Pension Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities
Year Ended December 31	2023	2022
Millions
Net Loss	$2.5	$11.4
Amortization of Prior Service Credit	0.1	0.1
Prior Service Credit Arising During the Period	—	0.8
Amortization of Loss	(5.7)	(11.4)
Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities	$(3.1)	$0.9


Information for Pension Plans with an Accumulated Benefit Obligation in Excess of Plan Assets
As of December 31	2023	2022
Millions
Projected Benefit Obligation	$746.3	$739.7
Accumulated Benefit Obligation	$729.5	$724.5
Fair Value of Plan Assets	$589.0	$568.6

NOTE 12. PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Continued)


Postretirement Health and Life Obligation and Funded Status
As of December 31	2023	2022
Millions
Change in Benefit Obligation
Obligation, Beginning of Year	$110.4	$148.2
Service Cost	2.0	3.0
Interest Cost	5.6	4.4
Actuarial Gain (a)	(9.3)	(38.7)
Benefits Paid	(8.1)	(9.2)
Participant Contributions	2.4	2.7
Plan Amendments (b)	(29.1)	—


Obligation, End of Year	$73.9	$110.4
Change in Plan Assets
Fair Value, Beginning of Year	$162.6	$201.8
Actual Return on Plan Assets	20.3	(33.0)
Employer Contribution (Withdrawal)	(3.4)	0.3
Participant Contributions	2.4	2.7
Benefits Paid	(8.1)	(9.2)
Fair Value, End of Year	$173.8	$162.6
Funded Status, End of Year	$99.9	$52.2

Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet Consist of:
Non-Current Assets	$106.3	$58.8
Current Liabilities	$(0.2)	$(0.2)
Non-Current Liabilities	$(6.2)	$(6.4)

(a)Actuarial gain in 2022 was primarily the result of increases in discount rates.

(b)In 2023, the postretirement health care plan was amended to change the company contribution to an annual stipend for certain retirees.

According to the accounting standards for retirement benefits, only assets in the VEBAs are treated as plan assets in the preceding table for the purpose of determining funded status. In addition to the postretirement health and life assets reported in the previous table, we had $12.8 million in irrevocable grantor trusts included in Other Non-Current Assets on the Consolidated Balance Sheet as of December 31, 2023 ($11.8 million as of December 31, 2022).


Unrecognized Postretirement Health and Life Costs
As of December 31	2023	2022
Millions
Net Gain	$(24.8)	$(9.2)
Prior Service Credit	(33.8)	(13.2)

Total Unrecognized Postretirement Health and Life Cost	$(58.6)	$(22.4)

NOTE 12. PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Continued)


Reconciliation of Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet
As of December 31	2023	2022
Millions
Net Gain (a)	$24.8	$9.2
Prior Service Credit	33.8	13.2
Accumulated Net Periodic Benefit Cost in Excess of Contributions (a)	41.3	29.8
Total Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet	$99.9	$52.2

(a)Excludes gains, losses and contributions associated with irrevocable grantor trusts.


Components of Net Periodic Postretirement Health and Life Cost
Year Ended December 31	2023	2022	2021
Millions
Service Cost	$2.0	$3.0	$3.6
Non-Service Cost Components (a)
Interest Cost	5.6	4.4	4.4
Expected Return on Plan Assets	(11.4)	(9.6)	(9.9)
Amortization of (Gain) Loss	(2.7)	0.4	3.0
Amortization of Prior Service Credit	(8.5)	(7.5)	(7.6)


Net Postretirement Health and Life Credit	$(15.0)	$(9.3)	$(6.5)

(a)These components of net periodic postretirement health and life cost are included in the line item “Other” under Other Income (Expense) on the Consolidated Statement of Income.


Other Changes in Postretirement Benefit Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities
Year Ended December 31	2023	2022
Millions
Net (Gain) Loss	$(18.3)	$3.9
Prior Service Credit Arising During the Period	(29.1)	—
Amortization of Prior Service Credit	8.4	7.5

Amortization of Gain (Loss)	2.7	(0.4)

Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities	$(36.3)	$11.0


Estimated Future Benefit Payments	Pension	Postretirement Health and Life
Millions
2024	$58.4	$6.3
2025	$58.1	$6.2
2026	$57.5	$6.1
2027	$57.2	$6.1
2028	$56.9	$6.0
Years 2029 – 2033	$272.6	$30.0

NOTE 12. PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Continued)


Weighted Average Assumptions Used to Determine Benefit Obligation
As of December 31	2023	2022
Discount Rate
Pension	5.39%	5.70%
Postretirement Health and Life	5.42%	5.68%
Rate of Compensation Increase	3.52%	3.58%
Health Care Trend Rates
Trend Rate	7.00%	6.50%
Ultimate Trend Rate	5.00%	5.00%
Year Ultimate Trend Rate Effective	2038	2038


Weighted Average Assumptions Used to Determine Net Periodic Benefit Costs
Year Ended December 31	2023	2022	2021
Discount Rate
Pension	5.70%	3.28%	2.87%
Postretirement Health and Life	5.89%	3.09%	2.70%
Expected Long-Term Return on Plan Assets
Pension	6.83%	6.00%	6.50%
Postretirement Health and Life	6.33%	5.41%	5.85%
Rate of Compensation Increase	3.58%	3.58%	3.62%

In establishing the expected long-term rate of return on plan assets, we determine the long-term historical performance of each asset class, adjust these for current economic conditions, and utilizing the target allocation of our plan assets, forecast the expected long-term rate of return.

The discount rate is computed using a bond matching study which utilizes a portfolio of high quality bonds that produce cash flows similar to the projected costs of our pension and other postretirement plans.

The Company utilizes actuarial assumptions about mortality to calculate the pension and postretirement health and life benefit obligations. The mortality assumptions used to calculate our pension and other postretirement benefit obligations as of December 31, 2023, considered a modified PRI-2012 mortality table and MP-2021 mortality projection scale.

NOTE 12. PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Continued)


Actual Plan Asset Allocations	Pension		Postretirement Health and Life (a)
	2023	2022	2023	2022
Equity Securities	57%	46%	67%	66%
Fixed Income Securities	40%	50%	33%	34%

Real Estate	3%	4%	—	—
	100%	100%	100%	100%

(a)Includes VEBAs and irrevocable grantor trusts.

There were no shares of ALLETE common stock included in pension plan equity securities as of December 31, 2023 (no shares as of December 31, 2022).

The defined benefit pension plans have adopted a dynamic asset allocation strategy (glide path) that increases the invested allocation to fixed income assets as the funding level of the plan increases to better match the sensitivity of the plan’s assets and liabilities to changes in interest rates. This is expected to reduce the volatility of reported pension plan expenses. The postretirement health and life plans’ assets are diversified to achieve strong returns within managed risk. Equity securities are diversified among domestic companies with large, mid and small market capitalization, as well as investments in international companies. The majority of debt securities are made up of investment grade bonds.

Following are the current targeted allocations as of December 31, 2023:


Plan Asset Target Allocations	Pension		Postretirement Health and Life (a)
Equity Securities	55	%	65	%
Fixed Income Securities	41	%	35	%

Real Estate	4	%	—
	100	%	100	%

(a)Includes VEBAs and irrevocable grantor trusts.

Fair Value

NOTE 12. PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Continued)

Fair Value (Continued)

Pension Fair Value


	Fair Value as of December 31, 2023
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets:
Equity Securities:
U.S. Large-cap (a)	—	$83.7	—	$83.7
U.S. Mid-cap Growth (a)	—	69.9	—	69.9
U.S. Small-cap (a)	—	46.5	—	46.5

International	$134.6	—	—	134.6



Fixed Income Securities (a)	—	215.0	—	215.0
Cash and Cash Equivalents	20.4	—	—	20.4


Real Estate	—	—	$18.9	18.9
Total Fair Value of Assets	$155.0	$415.1	$18.9	$589.0

(a)The underlying investments consist of actively-managed funds managed to achieve the returns of certain U.S. equity and fixed income securities indexes.


Recurring Fair Value Measures
Activity in Level 3						Real Estate
Millions
Balance as of December 31, 2022						$22.4
Actual Return on Plan Assets						(3.1)
Purchases, Sales, and Settlements – Net						(0.4)
Balance as of December 31, 2023						$18.9


	Fair Value as of December 31, 2022
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets:
Equity Securities:
U.S. Large-cap (a)	—	$61.2	—	$61.2
U.S. Mid-cap Growth (a)	—	40.0	—	40.0
U.S. Small-cap (a)	—	35.4	—	35.4

International	$127.0	—	—	127.0



Fixed Income Securities (a)	—	275.3	—	275.3
Cash and Cash Equivalents	7.3	—	—	7.3


Real Estate	—	—	$22.4	22.4
Total Fair Value of Assets	$134.3	$411.9	$22.4	$568.6

(a)The underlying investments consist of actively-managed funds managed to achieve the returns of certain U.S. equity and fixed income securities indexes.

NOTE 12. PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Continued)

Fair Value (Continued)


Recurring Fair Value Measures
Activity in Level 3									Real Estate
Millions
Balance as of December 31, 2021									$21.6
Actual Return on Plan Assets									1.0
Purchases, Sales, and Settlements – Net									(0.2)
Balance as of December 31, 2022									$22.4

Postretirement Health and Life Fair Value


	Fair Value as of December 31, 2023
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets:
Equity Securities: (a)
U.S. Large-cap	$30.0	—	—	$30.0
U.S. Mid-cap Growth	28.7	—	—	28.7
U.S. Small-cap	14.9	—	—	14.9
International	41.9	—	—	41.9
Fixed Income Securities:
Mutual Funds	55.1	—	—	55.1

Cash and Cash Equivalents	3.2	—	—	3.2


Total Fair Value of Assets	$173.8	—	—	$173.8

(a)The underlying investments consist of mutual funds (Level 1).


	Fair Value as of December 31, 2022
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets:
Equity Securities: (a)
U.S. Large-cap	$26.7	—	—	$26.7
U.S. Mid-cap Growth	25.5	—	—	25.5
U.S. Small-cap	12.7	—	—	12.7
International	41.5	—	—	41.5
Fixed Income Securities:
Mutual Funds	55.5	—	—	55.5
Cash and Cash Equivalents	0.7	—	—	0.7

Total Fair Value of Assets	$162.6	—	—	$162.6

(a)The underlying investments consist of mutual funds (Level 1).

NOTE 12. PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Continued)

Fair Value (Continued)


Recurring Fair Value Measures
Activity in Level 3			Private Equity Funds
Millions
Balance as of December 31, 2021			$2.0
Actual Return on Plan Assets			(1.5)
Purchases, Sales, and Settlements – Net			(0.5)
Balance as of December 31, 2022			—

Accounting and disclosure requirements for the Medicare Prescription Drug, Improvement and Modernization Act of 2003 (Act) provide guidance for employers that sponsor postretirement health care plans that provide prescription drug benefits. We provide a fully insured postretirement health benefit, including a prescription drug benefit, which qualifies us for a federal subsidy under the Act. The federal subsidy is reflected in the premiums charged to us by the insurance company.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 70
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480794/715-70-50-1

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480482/715-20-55-17

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(03)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (q)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (l)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//715/tableOfContent

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (o)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (p)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (r)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
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-Section 50
-Paragraph 1
-Subparagraph (r)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480126/715-20-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 60
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480266/715-60-50-3

+ Details

Fair Value - Recurring Fair Value Measures (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Liabilities:
Aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year or less	$ 1.3
Aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year to less than three years	3.2
Aggregate amount of available-for-sale corporate and governmental debt securities maturing in three years to less than five years	1.0
Aggregate amount of available-for-sale corporate and governmental debt securities maturing in five years or more	0.5
Recurring Fair Value Measures
Investments [Abstract]
Available-for-sale – Equity Securities	8.7	$ 7.7
Available-for-sale – Corporate and Governmental Debt Securities	6.0	5.7
Cash Equivalents	5.8	4.2
Total Fair Value of Assets	20.5	17.6
Liabilities:
Deferred Compensation	16.5	15.0
Total Fair Value of Liabilities	16.5	15.0
Recurring Fair Value Measures \| Level 1
Investments [Abstract]
Available-for-sale – Equity Securities	8.7	7.7
Available-for-sale – Corporate and Governmental Debt Securities	0.0	0.0
Cash Equivalents	5.8	4.2
Total Fair Value of Assets	14.5	11.9
Liabilities:
Deferred Compensation	0.0	0.0
Total Fair Value of Liabilities	0.0	0.0
Recurring Fair Value Measures \| Level 2
Investments [Abstract]
Available-for-sale – Equity Securities	0.0	0.0
Available-for-sale – Corporate and Governmental Debt Securities	6.0	5.7
Cash Equivalents	0.0	0.0
Total Fair Value of Assets	6.0	5.7
Liabilities:
Deferred Compensation	16.5	15.0
Total Fair Value of Liabilities	16.5	15.0
Recurring Fair Value Measures \| Level 3
Investments [Abstract]
Available-for-sale – Equity Securities	0.0	0.0
Available-for-sale – Corporate and Governmental Debt Securities	0.0	0.0
Cash Equivalents	0.0	0.0
Total Fair Value of Assets	0.0	0.0
Liabilities:
Deferred Compensation	0.0	0.0
Total Fair Value of Liabilities	$ 0.0	$ 0.0

Cover - USD ($)	12 Months Ended
Cover - USD ($)	Dec. 31, 2023	Feb. 01, 2024	Jun. 30, 2023
Document and Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	1-3548
Entity Registrant Name	ALLETE, Inc.
Entity Incorporation, State	MN
Entity Tax Identification Number	41-0418150
Entity Address, Address Line	30 West Superior Street
Entity Address, City	Duluth
Entity Address, State	MN
Entity Address, Postal Zip Code	55802-2093
City Area Code	218
Local Phone Number	279-5000
Title of 12(b) Security	Common Stock, without par value
Trading Symbol	ALE
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 3,320,941,939
Entity Common Stock, Shares Outstanding		57,578,222
Documents Incorporated by Reference	Portions of the Proxy Statement for the 2024 Annual Meeting of Shareholders are incorporated by reference in Part III.
Entity Central Index Key	0000066756
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false

Employee Stock and Incentive Plans - Share-Based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-Based Compensation Expense [Line Items]
Total Share-Based Compensation Expense	$ 3.9	$ 1.6	$ 3.0
Income Tax Benefit	1.1	0.5	0.9
Performance Shares
Share-Based Compensation Expense [Line Items]
Total Share-Based Compensation Expense	3.1	0.7	2.0
Restricted Stock Units
Share-Based Compensation Expense [Line Items]
Total Share-Based Compensation Expense	$ 0.8	$ 0.9	$ 1.0

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 1D
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480483/718-10-35-1D

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480483/718-10-35-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 2
-Subparagraph (a)(3)
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-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Section 50
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-Subparagraph (c)(1)(ii)
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Section 50
-Paragraph 2
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-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 2
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
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Reference 19: http://www.xbrl.org/2003/role/disclosureRef
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Reference 26: http://www.xbrl.org/2003/role/disclosureRef
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Reference 27: http://www.xbrl.org/2003/role/disclosureRef
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Reference 28: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Acquisitions - Narrative (Details) - New Energy - USD ($) $ in Millions		12 Months Ended
	Apr. 15, 2022	Dec. 31, 2022
Business Acquisition [Line Items]
Voting interests acquired	100.00%
Transaction purchase price	$ 165.5
Consideration transferred	$ 158.8
Acquisition related costs		$ 2.7

Fair Value - Narrative (Details) - USD ($)	12 Months Ended
Fair Value - Narrative (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Recurring Fair Value Measures [Line Items]
Equity Investments	$ 331,200,000	$ 322,700,000
Goodwill	154,900,000
Impairment of long-lived assets held-for-use	0	0	$ 0
Boswell Unit 3 \| 2021 Integrated Resource Plan \| MPUC
Recurring Fair Value Measures [Line Items]
Net book value	220,000,000
Boswell Unit 4 \| 2021 Integrated Resource Plan \| MPUC
Recurring Fair Value Measures [Line Items]
Net book value	420,000,000
Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis
Recurring Fair Value Measures [Line Items]
Impairment of long-lived assets held-for-use	0	0
Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis \| Regulated Operations
Recurring Fair Value Measures [Line Items]
Indicators of impairment	0	0
ATC
Recurring Fair Value Measures [Line Items]
Equity Investments	$ 179,700,000	$ 165,400,000	$ 154,500,000

Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2023

Selected Quarterly Financial Information [Abstract]

Quarterly Financial Data (Unaudited)


Quarter Ended	Mar. 31	Jun. 30	Sept. 30	Dec. 31
Millions Except Earnings Per Share
2023
Operating Revenue	$564.9	$533.4	$378.8	$402.7
Operating Income	$48.3	$53.5	$36.0	$43.1
Net Income Attributable to ALLETE	$58.2	$51.5	$85.9	$51.5
Earnings Per Share of Common Stock
Basic	$1.02	$0.90	$1.50	$0.89
Diluted	$1.02	$0.90	$1.49	$0.89
2022
Operating Revenue	$383.5	$373.1	$388.3	$425.8
Operating Income	$53.4	$13.7	$33.4	$33.7
Net Income Attributable to ALLETE	$66.3	$37.6	$33.7	$51.7
Earnings Per Share of Common Stock
Basic	$1.24	$0.67	$0.59	$0.90
Diluted	$1.24	$0.67	$0.59	$0.90
2021
Operating Revenue	$339.2	$335.6	$345.4	$399.0
Operating Income	$42.0	$28.2	$31.1	$50.0
Net Income Attributable to ALLETE	$51.8	$27.9	$27.6	$61.9
Earnings Per Share of Common Stock
Basic	$0.99	$0.53	$0.53	$1.18
Diluted	$0.99	$0.53	$0.53	$1.18

Common Stock and Earnings Per Share - Reconciliation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended												12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Basic
Net Income Attributable to ALLETE	$ 51.5	$ 85.9	$ 51.5	$ 58.2	$ 51.7	$ 33.7	$ 37.6	$ 66.3	$ 61.9	$ 27.6	$ 27.9	$ 51.8	$ 247.1	$ 189.3	$ 169.2
Average Common Shares (in shares)													57.3	55.9	52.4
Earnings Per Share (in dollars per share)	$ 0.89	$ 1.50	$ 0.90	$ 1.02	$ 0.90	$ 0.59	$ 0.67	$ 1.24	$ 1.18	$ 0.53	$ 0.53	$ 0.99	$ 4.31	$ 3.38	$ 3.23
Diluted
Net Income Attributable to ALLETE													$ 247.1	$ 189.3	$ 169.2
Average Common Shares (in shares)													57.4	56.0	52.5
Earnings Per Share (in dollars per share)	$ 0.89	$ 1.49	$ 0.90	$ 1.02	$ 0.90	$ 0.59	$ 0.67	$ 1.24	$ 1.18	$ 0.53	$ 0.53	$ 0.99	$ 4.30	$ 3.38	$ 3.23
Dilutive Securities (Shares)													0.1	0.1	0.1

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482635/260-10-55-15

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (e)(4)
-Publisher FASB
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 1
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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-Section S99
-Paragraph 2
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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Reference 15: http://www.xbrl.org/2003/role/exampleRef
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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

- Definition

Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities, and addition from assumption of issuance of common shares for dilutive potential common shares; of income (loss) available to common shareholders.

+ References + Details

Pension and Other Postretirement Benefit Plans - Reconciliation of Net Pension Amounts Recognized in Consolidated Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net Loss	$ (256.9)	$ (260.2)
Prior Service Credit	0.0	0.1
Accumulated Contributions in Excess of Net Periodic Benefit Cost (Prepaid Pension Asset)	99.6	89.0
Total Net Pension Amounts Recognized in Consolidated Balance Sheet	(157.3)	(171.1)
Postretirement Health and Life Obligation and Funded Status
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net Loss	24.8	9.2
Prior Service Credit	(33.8)	(13.2)
Accumulated Contributions in Excess of Net Periodic Benefit Cost (Prepaid Pension Asset)	41.3	29.8
Total Net Pension Amounts Recognized in Consolidated Balance Sheet	$ 99.9	$ 52.2

Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment and Estimated Useful Lives of Property, Plant and Equipment


Property, Plant and Equipment
As of December 31	2023	2022
Millions
Regulated Operations
Property, Plant and Equipment in Service	$5,167.2	$5,198.6

Construction Work in Progress	146.7	74.0
Accumulated Depreciation	(1,969.4)	(1,972.3)
Regulated Operations – Net	3,344.5	3,300.3
ALLETE Clean Energy
Property, Plant and Equipment in Service	1,612.8	1,619.4
Construction Work in Progress	48.9	51.1
Accumulated Depreciation	(229.1)	(176.8)
ALLETE Clean Energy – Net	1,432.6	1,493.7






Corporate and Other (a)
Property, Plant and Equipment in Service	355.8	295.2
Construction Work in Progress	27.5	50.9
Accumulated Depreciation	(147.0)	(136.1)
Corporate and Other – Net	236.3	210.0
Property, Plant and Equipment – Net	$5,013.4	$5,004.0

(a)Primarily includes BNI Energy and a small amount of non-rate base generation.

Estimated Useful Lives of Property, Plant and Equipment (Years)

Regulated Operations

Generation

4 to 50

ALLETE Clean Energy

5 to 35

Transmission

50 to 75

Corporate and Other

3 to 50

Distribution

18 to 70

Asset Retirement Obligations


Asset Retirement Obligations
Millions
Obligation as of December 31, 2021						$184.5
Accretion						9.5
Liabilities Recognized						7.8
Liabilities Settled						(4.4)
Revisions in Estimated Cash Flows						3.0
Obligation as of December 31, 2022						200.4
Accretion						10.3

Liabilities Settled						(10.2)
Revisions in Estimated Cash Flows						2.4
Obligation as of December 31, 2023						$202.9

Schedule II (Details) - USD ($) $ in Millions	12 Months Ended
Schedule II (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Trade Accounts Receivable
Valuation and Qualifying Accounts and Reserves [Roll Forward]
Balance at Beginning of Period	$ 1.6	$ 1.8	$ 2.5
Charged to Income	1.3	1.9	1.2
Other Charges	0.0	0.0	0.0
Deductions from Reserves	1.3	2.1	1.9
Balance at End of Period	1.6	1.6	1.8
Deferred Tax Assets
Valuation and Qualifying Accounts and Reserves [Roll Forward]
Balance at Beginning of Period	60.2	69.0	69.9
Charged to Income	(2.2)	(8.8)	(0.9)
Other Charges	0.0	0.0	0.0
Deductions from Reserves	0.0	0.0	0.0
Balance at End of Period	$ 58.0	$ 60.2	$ 69.0

Income Tax Expense (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Tax Expense


Income Tax Expense
Year Ended December 31	2023	2022	2021
Millions
Current Income Tax Expense (a)
Federal	$9.4	$1.2	—
State	0.9	6.1	—
Total Current Income Tax Expense	$10.3	$7.3	—
Deferred Income Tax Expense (Benefit)
Federal (b)	$(6.0)	$(32.8)	$(37.2)

State (c)	24.0	(5.2)	10.8

Investment Tax Credit Amortization	(0.4)	(0.5)	(0.5)
Total Deferred Income Tax Expense (Benefit)	$17.6	$(38.5)	$(26.9)
Total Income Tax Expense (Benefit)	$27.9	$(31.2)	$(26.9)

(a)For the years ended December 31, 2023 and 2022, the federal current tax expense was partially offset by production tax credits and NOLs. For the year ended December 31, 2021, the federal and state current tax expense was minimal due to NOLs.

(b)For the year ended December 31, 2023, the federal deferred income tax benefit was due to tax credits, partially offset by deferred partnership income. For the years ended December 31, 2022 and 2021, the federal deferred income tax benefit is primarily due to production tax credits.

(c)For the year ended December 31, 2022, the state impact includes the benefit of deferred repricing as a result of the New Energy acquisition.

Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense


Reconciliation of Taxes from Federal Statutory
Rate to Total Income Tax Expense
Year Ended December 31	2023		2022		2021
Millions
Income Before Non-Controlling Interest and Income Taxes	$206.8		$100.1		$110.9
Statutory Federal Income Tax Rate	21	%	21	%	21	%
Income Taxes Computed at Statutory Federal Rate	$43.4		$21.0		$23.3
Increase (Decrease) in Tax Due to:
State Income Taxes – Net of Federal Income Tax Benefit	19.7		8.6		8.6
Deferred Revaluation – Net of Federal Income Tax Benefit	—		(7.9)		—


Production Tax Credits (a)	(31.6)		(50.7)		(53.5)
Investment Tax Credits (a)	(5.8)		(4.1)		—
Regulatory Differences – Excess Deferred Tax Benefit	(9.9)		(9.1)		(9.5)


Non-Controlling Interest	13.3		11.2		6.3
AFUDC - Equity	(1.3)		(1.1)		(1.0)
Other	0.1		0.9		(1.1)
Total Income Tax Expense (Benefit)	$27.9		$(31.2)		$(26.9)

(a)For the year ended December 31, 2023, the credits are presented net of any estimated discount on the sale of certain credits.

Deferred Tax Assets and Liabilities


Deferred Income Tax Assets and Liabilities
As of December 31	2023	2022
Millions
Deferred Income Tax Assets
Employee Benefits and Compensation	$29.3	$46.4
Property-Related	58.1	61.9
NOL Carryforwards	13.0	16.7
Capital Loss Carryforwards	2.1	13.1
Tax Credit Carryforwards	557.4	548.7
Power Sales Agreements	9.0	13.7
Regulatory Liabilities	89.0	95.5
Other	8.7	28.1
Gross Deferred Income Tax Assets	766.6	824.1
Deferred Income Tax Asset Valuation Allowance	(58.0)	(60.2)
Total Deferred Income Tax Assets	$708.6	$763.9
Deferred Income Tax Liabilities
Deferred Gain	$7.9	$7.9
Property-Related	632.0	661.7
Regulatory Asset for Benefit Obligations	48.1	57.7
Unamortized Investment Tax Credits	29.6	30.0
Partnership Basis Differences	156.5	126.0
Fuel Adjustment Clause	1.9	10.7
Regulatory Assets	25.3	28.0

Total Deferred Income Tax Liabilities	$901.3	$922.0
Net Deferred Income Taxes (a)	$192.7	$158.1

(a)Recorded as a net Deferred Income Tax liability on the Consolidated Balance Sheet.

NOL and Tax Credit Carryforwards


NOL and Tax Credit Carryforwards
As of December 31	2023	2022
Millions

Federal Tax Credit Carryforwards	$480.4	$464.5
Federal Capital Loss Carryforwards (a)	—	$35.1
State NOL Carryforwards (a)	$280.9	$323.0
State Tax Credit Carryforwards (b)	$21.5	$24.5
State Capital Loss Carryforwards (a)	—	$83.2

(a)Pre-tax amounts; state NOL carryforwards net of a $10.5 million valuation allowance and state capital loss carryforwards net of a $58.7 million valuation allowance.

(b)Net of a $55.4 million valuation allowance as of December 31, 2023 ($59.6 million as of December 31, 2022).

Gross Unrecognized Income Tax Benefits


Gross Unrecognized Income Tax Benefits	2023	2022	2021
Millions
Balance at January 1	$1.3	$1.3	$1.4


Reductions for Tax Positions Related to Prior Years	(0.2)	—	(0.1)


Balance as of December 31	$1.1	$1.3	$1.3

Operations and Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents	$ 71.9	$ 36.4	$ 45.1
Restricted Cash included in Prepayments and Other	5.1	1.5	0.3
Restricted Cash included in Other Non-Current Assets	2.4	2.3	2.3
Cash, Cash Equivalents and Restricted Cash on the Consolidated Statement of Cash Flows	$ 79.4	$ 40.2	$ 47.7	$ 65.2

Business Segment - Narrative (Details)	12 Months Ended
Business Segment - Narrative (Details)	Dec. 31, 2023 segment
Business Segments [Line Items]
Number of reportable segments	2
Regulated Operations
Business Segments [Line Items]
Number of operating segments	3
Corporate and Other
Business Segments [Line Items]
Number of operating segments	3

Equity Investments (Tables)

12 Months Ended

Dec. 31, 2023

Equity Method Investments and Joint Ventures [Abstract]

Equity Investments


ALLETE’s Investment in ATC
Year Ended December 31	2023	2022
Millions
Equity Investment Beginning Balance	$165.4	$154.5
Cash Investments	8.2	5.9
Equity in ATC Earnings	23.1	19.3
Distributed ATC Earnings	(18.3)	(15.5)

Amortization of the Remeasurement of Deferred Income Taxes	1.3	1.2
Equity Investment Ending Balance	$179.7	$165.4


ATC Summarized Financial Data
Balance Sheet Data
As of December 31	2023	2022
Millions
Current Assets	$115.2	$89.6
Non-Current Assets	6,337.0	5,997.8
Total Assets	$6,452.2	$6,087.4
Current Liabilities	$495.9	$511.9
Long-Term Debt	2,736.0	2,613.0
Other Non-Current Liabilities	585.2	485.8
Members’ Equity	2,635.1	2,476.7
Total Liabilities and Members’ Equity	$6,452.2	$6,087.4


Income Statement Data
Year Ended December 31	2023	2022	2021
Millions
Revenue	$818.9	$751.2	$754.8
Operating Expense	407.6	381.5	376.2
Other Expense	131.7	122.9	113.9
Net Income	$279.6	$246.8	$264.7
ALLETE’s Equity in Net Income	$23.1	$19.3	$21.3


ALLETE’s Investment in Nobles 2
Millions
Equity Investment Balance as of December 31, 2022			$157.3

Equity in Nobles 2 Earnings (a)			(1.4)
Distributed Nobles 2 Earnings			(4.4)
Equity Investment Balance as of December 31, 2023			$151.5

(a)The Company also recorded net loss attributable to non-controlling interest of $10.2 million related to its investment in Nobles 2

Operations and Significant Accounting Policies - Accounts Receivable (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Trade Accounts Receivable
Billed	$ 106.8	$ 107.1
Unbilled	23.8	29.2
Less: Allowance for Doubtful Accounts	1.6	1.6
Total Trade Accounts Receivable	129.0	134.7
Income Taxes Receivable	8.2	3.2
Total Accounts Receivable	$ 137.2	$ 137.9

Jointly-Owned Facilities and Assets - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) MW	Dec. 31, 2022
Boswell Unit 4 \| Boswell Unit 4
Jointly-Owned Facilities and Assets [Line Items]
% Ownership	80.00%	80.00%
Generating capacity jointly owned (MW) \| MW	585
Boswell Unit 4 \| Boswell Unit 4 \| Minnesota Power
Jointly-Owned Facilities and Assets [Line Items]
% Ownership	80.00%
Boswell Unit 4 \| Boswell Unit 4 \| WPPI Energy
Jointly-Owned Facilities and Assets [Line Items]
WPPI Energy ownership	20.00%
Nemadji Trail Energy Center
Jointly-Owned Facilities and Assets [Line Items]
Estimated capital expenditures, including past expenditures \| $	$ 700
Nemadji Trail Energy Center \| Natural Gas-Fired
Jointly-Owned Facilities and Assets [Line Items]
Generating capacity jointly owned (MW) \| MW	600
Nemadji Trail Energy Center \| South Shore Energy
Jointly-Owned Facilities and Assets [Line Items]
Capital cost spent to date \| $	$ 9
Nemadji Trail Energy Center \| South Shore Energy \| Natural Gas-Fired
Jointly-Owned Facilities and Assets [Line Items]
Expected output entitlement	20.00%

Short-Term and Long-Term Debt

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Short-Term and Long-Term Debt

SHORT-TERM AND LONG-TERM DEBT

Short-Term Debt. As of December 31, 2023, total short-term debt outstanding was $111.4 million ($272.6 million as of December 31, 2022), and consisted of long-term debt due within one year and included $0.1 million of unamortized debt issuance costs.

On October 17, 2023, ALLETE amended its $400 million credit facility (Credit Agreement), which was scheduled to expire in January 2026, to $355 million and extended the expiration date to January 10, 2027. The amended Credit Agreement is unsecured and has a variable interest rate. ALLETE may request a single, one-year extension to the expiration date. Advances may be used by ALLETE for general corporate purposes, to provide liquidity in support of ALLETE's commercial paper program and to issue up to $100 million in letters of credit.

As of December 31, 2023, we had consolidated bank lines of credit aggregating to $423.1 million ($475.7 million as of December 31, 2022), most of which expire in January 2027. We had $19.4 million outstanding in standby letters of credit and $34.1 million outstanding draws under our lines of credit as of December 31, 2023 ($32.8 million in standby letters of credit and $31.3 million outstanding draws as of December 31, 2022).

Long-Term Debt. As of December 31, 2023, total long-term debt outstanding was $1,679.9 million ($1,648.2 million as of December 31, 2022) and included $8.0 million of unamortized debt issuance costs. The aggregate amount of long-term debt maturing in 2024 is $111.4 million; $244.7 million in 2025; $80.2 million in 2026; $162.5 million in 2027; $55.8 million in 2028; and $1,144.8 million thereafter. Substantially all of our regulated electric plant is subject to the lien of the mortgages collateralizing outstanding first mortgage bonds. The mortgages contain non-financial covenants customary in utility mortgages, including restrictions on our ability to incur liens, dispose of assets, and merge with other entities.

Minnesota Power is obligated to make financing payments for the Camp Ripley solar array totaling $1.4 million annually during the financing term, which expires in 2027. Minnesota Power has the option at the end of the financing term to renew for a two year term, or to purchase the solar array for approximately $4 million. Minnesota Power anticipates exercising the purchase option when the term expires.

On April 27, 2023, ALLETE issued $125 million of its First Mortgage Bonds (Bonds) to certain institutional buyers in the private placement market. The Bonds, which bear interest at 4.98 percent, will mature in April 2033 and pay interest semi-annually in May and November of each year, commencing on November 1, 2023. ALLETE has the option to prepay all or a portion of the Bonds at its discretion, subject to a make-whole provision. The Bonds are subject to additional terms and conditions which are customary for these types of transactions. Proceeds from the sale of the Bonds were used to refinance existing indebtedness and for general corporate purposes. The Bonds were sold in reliance on an exemption from registration under Section 4(a)(2) of the Securities Act of 1933, as amended, to institutional accredited investors.

NOTE 8. SHORT-TERM AND LONG-TERM DEBT (Continued)

Long-Term Debt (Continued)


Long-Term Debt
As of December 31	2023	2022
Millions
First Mortgage Bonds
6.02% Series Due 2023	—	$75.0
3.69% Series Due 2024	$60.0	60.0
4.90% Series Due 2025	30.0	30.0
5.10% Series Due 2025	30.0	30.0
3.20% Series Due 2026	75.0	75.0
5.99% Series Due 2027	60.0	60.0
3.30% Series Due 2028	40.0	40.0
4.08% Series Due 2029	70.0	70.0
3.74% Series Due 2029	50.0	50.0
2.50% Series Due 2030	46.0	46.0
3.86% Series Due 2030	60.0	60.0
2.79% Series Due 2031	100.0	100.0
4.54% Series Due 2032	75.0	75.0
4.98% Series Due 2033	125.0	—
5.69% Series Due 2036	50.0	50.0
6.00% Series Due 2040	35.0	35.0
5.82% Series Due 2040	45.0	45.0
4.08% Series Due 2042	85.0	85.0
4.21% Series Due 2043	60.0	60.0
4.95% Series Due 2044	40.0	40.0
5.05% Series Due 2044	40.0	40.0
4.39% Series Due 2044	50.0	50.0
4.07% Series Due 2048	60.0	60.0
4.47% Series Due 2049	30.0	30.0
3.30% Series Due 2050	94.0	94.0
Armenia Mountain Senior Secured Notes 3.26% Due 2024	9.5	19.3
Industrial Development Variable Rate Demand Refunding Revenue Bonds Series 2006, Due 2025	27.8	27.8
Revolving Credit Facility Variable Rate Due 2027	—	13.0
Senior Unsecured Notes 2.65% Due 2025	150.0	150.0
Senior Unsecured Notes 3.11% Due 2027	80.0	80.0
SWL&P First Mortgage Bonds 4.15% Series Due 2028	15.0	15.0
SWL&P First Mortgage Bonds 4.14% Series Due 2048	12.0	12.0
Unsecured Term Loan Variable Rate Due 2023	—	170.0
Other Long-Term Debt, 2023 Weighted Average Rate 5.24% Due 2024 – 2051	95.1	82.0
Unamortized Debt Issuance Costs	(8.1)	(8.3)
Total Long-Term Debt	1,791.3	1,920.8
Less: Due Within One Year	111.4	272.6
Net Long-Term Debt	$1,679.9	$1,648.2

NOTE 8. SHORT-TERM AND LONG-TERM DEBT (Continued)

Long-Term Debt (Continued)

Financial Covenants. Our long-term debt arrangements contain customary covenants. In addition, our lines of credit and letters of credit supporting certain long-term debt arrangements contain financial covenants. Our compliance with financial covenants is not dependent on debt ratings. The most restrictive financial covenant requires ALLETE to maintain a ratio of indebtedness to total capitalization (as the amounts are calculated in accordance with the respective long-term debt arrangements) of less than or equal to 0.65 to 1.00, measured quarterly. As of December 31, 2023, our ratio was approximately 0.36 to 1.00. Failure to meet this covenant would give rise to an event of default if not cured after notice from the lender, in which event ALLETE may need to pursue alternative sources of funding. Some of ALLETE’s debt arrangements contain “cross-default” provisions that would result in an event of default if there is a failure under other financing arrangements to meet payment terms or to observe other covenants that would result in an acceleration of payments due. ALLETE has no significant restrictions on its ability to pay dividends from retained earnings or net income. As of December 31, 2023, ALLETE was in compliance with its financial covenants.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 470
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//470/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

+ Details

Jointly-Owned Facilities and Assets (Tables)

12 Months Ended

Dec. 31, 2023

Jointly-Owned Facilities and Assets [Abstract]

Jointly-Owned Facilities and Assets

Minnesota Power’s investments in jointly-owned facilities and assets and the related ownership percentages are as follows:


Regulated Utility Plant	Plant in Service	Accumulated Depreciation	Construction Work in Progress	% Ownership
Millions
As of December 31, 2023
Boswell Unit 4	$725.9	$369.8	$2.8	80
Transmission Assets	101.0	23.6	—	9.3 - 14.7
Total	$826.9	$393.4	$2.8
As of December 31, 2022
Boswell Unit 4	$712.0	$340.1	$3.3	80
Transmission Assets	101.0	21.1	—	9.3 - 14.7
Total	$813.0	$361.2	$3.3

Property, Plant and Equipment - Property, Plant and Equipment and Estimated Useful Lives of Property, Plant and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment – Net	$ 5,013.4	$ 5,004.0
Regulated Operations
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment in Service	5,167.2	5,198.6
Construction Work in Progress	146.7	74.0
Accumulated Depreciation	(1,969.4)	(1,972.3)
Property, Plant and Equipment – Net	3,344.5	3,300.3
ALLETE Clean Energy
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment in Service	1,612.8	1,619.4
Construction Work in Progress	48.9	51.1
Accumulated Depreciation	(229.1)	(176.8)
Property, Plant and Equipment – Net	1,432.6	1,493.7
Corporate and Other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment in Service	355.8	295.2
Construction Work in Progress	27.5	50.9
Accumulated Depreciation	(147.0)	(136.1)
Property, Plant and Equipment – Net	$ 236.3	$ 210.0
Minimum \| ALLETE Clean Energy
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Minimum \| Corporate and Other
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Maximum \| ALLETE Clean Energy
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	35 years
Maximum \| Corporate and Other
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	50 years
Generation \| Minimum \| Regulated Operations
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	4 years
Generation \| Maximum \| Regulated Operations
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	50 years
Transmission \| Minimum \| Regulated Operations
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	50 years
Transmission \| Maximum \| Regulated Operations
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	75 years
Distribution \| Minimum \| Regulated Operations
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	18 years
Distribution \| Maximum \| Regulated Operations
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	70 years

Income Tax Expense - Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense [Abstract]
Income Before Non-Controlling Interest and Income Taxes	$ 206.8	$ 100.1	$ 110.9
Income Taxes Computed at Statutory Federal Rate	43.4	21.0	23.3
Increase (Decrease) in Tax Due to:
State Income Taxes – Net of Federal Income Tax Benefit	19.7	8.6	8.6
Deferred Revaluation – Net of Federal Income Tax Benefit	0.0	(7.9)	0.0
Production Tax Credits	(31.6)	(50.7)	(53.5)
Investment Tax Credits	(5.8)	(4.1)	0.0
Regulatory Differences – Excess Deferred Tax Benefit	(9.9)	(9.1)	(9.5)
Non-Controlling Interest	13.3	11.2	6.3
AFUDC - Equity	(1.3)	(1.1)	(1.0)
Other	0.1	0.9	(1.1)
Total Income Tax Expense (Benefit)	$ 27.9	$ (31.2)	$ (26.9)

Acquisitions

12 Months Ended

Dec. 31, 2023

Business Combination and Asset Acquisition [Abstract]

Acquisitions

ACQUISITIONS

2022 Activity

New Energy. On April 15, 2022, a wholly-owned subsidiary of ALLETE acquired 100 percent of the membership interests of New Energy for a purchase price of $165.5 million. Total consideration of approximately $158.8 million was paid in cash on the acquisition date, which is net of cash acquired and debt assumed. New Energy, which is headquartered in Annapolis, Maryland, is a renewable energy development company with a primary focus on solar and storage facilities while also offering comprehensive operations, maintenance and asset management services. The acquisition of New Energy is consistent with ALLETE’s stated strategy of additional investment in renewable energy and related infrastructure across North America to support the Company’s sustainability-in-action strategy while providing potential long-term earnings growth.

The acquisition was accounted for as a business combination and the purchase price was allocated based on the estimated fair values of the assets acquired and the liabilities assumed at the date of acquisition. The allocation of the purchase price, which was finalized in the fourth quarter of 2022, is shown in the following table. Fair value measurements were valued primarily using the discounted cash flow method and replacement cost basis. The goodwill recorded is primarily attributable to the highly skilled workforce of New Energy and synergies expected to arise as a result of the acquisition.

The Company has not presented separate results of operations since closing or combined pro forma financial information of the Company and New Energy since the beginning of 2021, as the results of operations for New Energy are not material to the Company's consolidated financials.


Millions
Assets Acquired
Cash and Cash Equivalents												$3.9
Accounts Receivable												1.4
Inventory (a)												25.3
Other Current Assets												12.8
Property, Plant and Equipment - Net												16.4
Goodwill (b)												154.9
Other Non-Current Assets												2.1
Total Assets Acquired												$216.8
Liabilities Assumed
Current Liabilities												$23.6
Long-Term Debt Due Within One Year												28.3
Long-Term Debt												5.9
Other Non-Current Liabilities												0.2
Total Liabilities Assumed												$58.0
Net Identifiable Assets Acquired												$158.8

(a)Includes $11.6 million of purchase price accounting for certain projects under development at the time of acquisition.

(b)For tax purpose, the purchase price allocation resulted in $154.9 million of deductible goodwill.

Acquisition-related costs were $2.7 million after-tax, expensed as incurred during 2022 and recorded in Operating and Maintenance on the Consolidated Statement of Income.

Commitments, Guarantees and Contingencies - Power Purchase Agreements (Details) - Square Butte - Square Butte PPA $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) MW	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Power Purchase Agreements [Line Items]
Ppa counterparty total debt outstanding	$ 171.8
Minnesota Power
Power Purchase Agreements [Line Items]
Cost of purchased power	86.2	$ 82.7	$ 82.4
Pro rata share of ppa counterparty interest expense	$ 5.5	$ 5.1	$ 5.8
Square Butte Coal-fired Unit
Power Purchase Agreements [Line Items]
Generating capacity counterparty owned (MW) \| MW	455
Square Butte Coal-fired Unit \| Minnesota Power
Power Purchase Agreements [Line Items]
Expected output entitlement	50.00%
Ppa annual debt service obligation	50.00%
2024-01-01 \| Square Butte Coal-fired Unit \| Minnesota Power
Power Purchase Agreements [Line Items]
Ppa counterparty annual debt service through 2027	$ 33.5
2025-01-01 \| Square Butte Coal-fired Unit \| Minnesota Power
Power Purchase Agreements [Line Items]
Ppa counterparty annual debt service through 2027	29.5
2026-01-01 \| Square Butte Coal-fired Unit \| Minnesota Power
Power Purchase Agreements [Line Items]
Ppa counterparty annual debt service through 2027	29.6
2027-01-01 \| Square Butte Coal-fired Unit \| Minnesota Power
Power Purchase Agreements [Line Items]
Ppa counterparty annual debt service through 2027	$ 11.9

Schedule II

12 Months Ended

Dec. 31, 2023

SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]

Schedule II

ALLETE

Valuation and Qualifying Accounts and Reserves


	Balance at Beginning of Period	Additions		Deductions from Reserves (a)	Balance at End of Period
		Charged to Income	Other Charges
Millions
Reserve Deducted from Related Assets
Reserve For Uncollectible Accounts
2021 Trade Accounts Receivable	$2.5	$1.2	—	$1.9	$1.8

2022 Trade Accounts Receivable	$1.8	$1.9	—	$2.1	$1.6

2023 Trade Accounts Receivable	$1.6	$1.3	—	$1.3	$1.6

Deferred Asset Valuation Allowance
2021 Deferred Tax Assets	$69.9	$(0.9)	—	—	$69.0
2022 Deferred Tax Assets	$69.0	$(8.8)	—	—	$60.2
2023 Deferred Tax Assets	$60.2	$(2.2)	—	—	$58.0

(a) Includes uncollectible accounts written-off.

Jointly-Owned Facilities and Assets - Table (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Jointly-Owned Facilities and Assets [Line Items]
Plant in Service	$ 826.9	$ 813.0
Accumulated Depreciation	393.4	361.2
Construction Work in Progress	2.8	3.3
Transmission Assets \| Transmission Assets
Jointly-Owned Facilities and Assets [Line Items]
Plant in Service	101.0	101.0
Accumulated Depreciation	23.6	21.1
Construction Work in Progress	$ 0.0	$ 0.0
Transmission Assets \| Transmission Assets \| Minimum
Jointly-Owned Facilities and Assets [Line Items]
% Ownership	9.30%	9.30%
Transmission Assets \| Transmission Assets \| Maximum
Jointly-Owned Facilities and Assets [Line Items]
% Ownership	14.70%	14.70%
Boswell Unit 4 \| Boswell Unit 4
Jointly-Owned Facilities and Assets [Line Items]
Plant in Service	$ 725.9	$ 712.0
Accumulated Depreciation	369.8	340.1
Construction Work in Progress	$ 2.8	$ 3.3
% Ownership	80.00%	80.00%

Business Segment - Table (Details) - USD ($) $ in Millions	3 Months Ended												12 Months Ended
Business Segment - Table (Details) - USD ($) $ in Millions	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Revenue	$ 402.7	$ 378.8	$ 533.4	$ 564.9	$ 425.8	$ 388.3	$ 373.1	$ 383.5	$ 399.0	$ 345.4	$ 335.6	$ 339.2	$ 1,879.8	$ 1,570.7	$ 1,419.2
Other – Non-utility													5.1	7.6	11.4
Net Income Attributable to ALLETE	51.5	$ 85.9	$ 51.5	$ 58.2	51.7	$ 33.7	$ 37.6	$ 66.3	$ 61.9	$ 27.6	$ 27.9	$ 51.8	247.1	189.3	169.2
Total Depreciation and Amortization													251.8	242.2	231.7
Total Interest Expense													80.8	75.2	69.1
Equity Earnings													21.7	18.7	20.0
Income Tax Expense (Benefit)													27.9	(31.2)	(26.9)
Total Assets	6,656.4				6,845.6								6,656.4	6,845.6
Total Capital Expenditures													256.0	208.1
New Energy
Segment Reporting Information [Line Items]
Acquisition related costs														2.7
Operating Segments
Segment Reporting Information [Line Items]
Total Depreciation and Amortization													251.8	242.2	231.7
Eliminations
Segment Reporting Information [Line Items]
Total Interest Expense													(6.4)	(4.8)	(2.9)
Regulated Operations
Segment Reporting Information [Line Items]
Revenue													1,238.3	1,259.3	1,227.9
Net Income Attributable to ALLETE													147.2	149.9	129.1
Equity Earnings													23.1	19.3	21.3
Income Tax Expense (Benefit)													22.4	(10.4)	(16.6)
Total Assets	4,335.0				4,291.4								4,335.0	4,291.4
Total Capital Expenditures													236.3	158.3
Regulated Operations \| Operating Segments
Segment Reporting Information [Line Items]
Total Depreciation and Amortization													179.2	171.9	170.7
Total Interest Expense													63.9	58.1	57.3
ALLETE Clean Energy
Segment Reporting Information [Line Items]
Revenue													418.5	118.3	86.9
Net Income Attributable to ALLETE													71.7	16.3	26.3
Income Tax Expense (Benefit)													2.7	(15.4)	(16.6)
Total Assets	1,594.1				1,873.3								1,594.1	1,873.3
Total Capital Expenditures													(5.3)	2.2
Gain From Legal Settlements - after-tax													44.3
ALLETE Clean Energy \| Operating Segments
Segment Reporting Information [Line Items]
Total Depreciation and Amortization													57.5	58.6	49.2
Total Interest Expense													0.8	2.3	1.5
Corporate and Other
Segment Reporting Information [Line Items]
Revenue													223.0	193.1	104.4
Net Income Attributable to ALLETE													28.2	23.1	13.8
Purchase price accounting - after tax														8.3
Total Assets	$ 727.3				$ 680.9								727.3	680.9
Total Capital Expenditures													25.0	47.6
Corporate and Other \| New Energy
Segment Reporting Information [Line Items]
Acquisition related costs														2.7
Corporate and Other \| Nemadji Trail Energy Center \| South Shore Energy
Segment Reporting Information [Line Items]
Gain on sale after tax														8.5
Corporate and Other \| Operating Segments
Segment Reporting Information [Line Items]
Total Depreciation and Amortization													15.1	11.7	11.8
Corporate and Other \| Corporate and Other
Segment Reporting Information [Line Items]
Total Interest Expense													22.5	19.6	13.2
Equity Earnings													(1.4)	(0.6)	(1.3)
Income Tax Expense (Benefit)													2.8	(5.4)	6.3
Residential \| Regulated Operations
Segment Reporting Information [Line Items]
Operating Revenue													165.7	175.9	160.8
Commercial \| Regulated Operations
Segment Reporting Information [Line Items]
Operating Revenue													184.6	187.2	168.6
Municipal \| Regulated Operations
Segment Reporting Information [Line Items]
Operating Revenue													33.4	40.2	52.0
Industrial \| Regulated Operations
Segment Reporting Information [Line Items]
Operating Revenue													593.6	589.0	565.5
Other Power Suppliers \| Regulated Operations
Segment Reporting Information [Line Items]
Operating Revenue													146.1	165.8	168.7
Other \| Regulated Operations
Segment Reporting Information [Line Items]
Operating Revenue													114.9	101.2	112.3
Long-term PSA \| ALLETE Clean Energy
Segment Reporting Information [Line Items]
Operating Revenue													65.0	77.2	75.5
Sale of Wind Energy Facilities \| ALLETE Clean Energy
Segment Reporting Information [Line Items]
Operating Revenue													348.4	33.5	0.0
Other \| ALLETE Clean Energy
Segment Reporting Information [Line Items]
Other – Non-utility													5.1	7.6	11.4
Long-term Contract \| Corporate and Other
Segment Reporting Information [Line Items]
Operating Revenue													101.2	89.2	84.4
Sale of Renewable Development Projects \| Corporate and Other
Segment Reporting Information [Line Items]
Operating Revenue													92.5	73.9	0.0
Other \| Corporate and Other
Segment Reporting Information [Line Items]
Operating Revenue													$ 29.3	$ 30.0	$ 20.0

Commitments, Guarantees and Contingencies (Tables)

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Estimated Minimum Annual Payments for Certain Long-Term Commitments

The following table details the estimated minimum payments for certain long-term commitments as of December 31, 2023:


	2024	2025	2026	2027	2028	Thereafter
Millions

Capital Purchase Obligations	$73.9	$1.6	$9.9	$38.1	—	$10.5
Easements (a)	$8.0	$8.1	$8.1	$8.2	$8.4	$217.7
PPAs (b)	$140.7	$133.8	$136.6	$125.7	$132.4	$937.5
Other Purchase Obligations (c)	$42.9	—	—	—	—	—

(a)Easement obligations represent the minimum payments for our land easement agreements at our wind energy facilities.

(b)Does not include the Oliver Wind I, Oliver Wind II or Nobles 2 PPAs, as Minnesota Power only pays for energy as it is delivered. (See Power Purchase Agreements.)

(c)Consists of long-term service agreements for wind energy facilities and minimum purchase commitments under coal and rail contracts.

Minnesota Power has also entered into the following long-term PPAs for the purchase of capacity and energy as of December 31, 2023:

Counterparty

Quantity

Product

Commencement

Expiration

Pricing

PPAs

Calpine Corporation

25 MW

Capacity

June 2019

May 2026

Fixed

Manitoba Hydro

PPA 1

250 MW

Capacity / Energy

June 2020

May 2035

(a)

PPA 2

133 MW

Energy

June 2020

June 2040

Forward Market Prices

Nobles 2

250 MW

Capacity / Energy

December 2020

December 2040

Fixed

Oliver Wind I

(b)

Energy

December 2006

December 2040

Fixed

Oliver Wind II

(b)

Energy

December 2007

December 2040

Fixed

(b)The PPAs provide for the purchase of all output from the 50 MW Oliver Wind I and 48 MW Oliver Wind II wind energy facilities.

Minnesota Power has also entered into the following long-term PSAs for the sale of capacity and energy as of December 31, 2023:

Counterparty

Quantity

Product

Commencement

Expiration

Pricing

PSAs

Basin

PSA 1

(a)

Capacity

June 2022

May 2025

Fixed

PSA 2

100 MW

Capacity

June 2025

May 2028

Fixed

Great River Energy

100 MW

Capacity

June 2022

May 2025

Fixed

Minnkota Power

(b)

Capacity / Energy

June 2014

December 2026

(b)

Oconto Electric Cooperative

25 MW

Capacity / Energy

January 2019

May 2026

Fixed

Silver Bay Power

(c)

Energy

January 2017

December 2031

(d)

(a)The agreement provided for 75 MW of capacity from June 1, 2022, through May 31, 2023, and increased to 125 MW of capacity from June 1, 2023, through May 31, 2025.

(c)Silver Bay Power supplies approximately 90 MW of load to Northshore Mining, an affiliate of Silver Bay Power.

(d)The energy pricing escalates at a fixed rate annually and is adjusted for changes in a natural gas index.

Pension and Other Postretirement Benefit Plans - Assumptions Used to Determine Benefit Obligation and Net Periodic Benefit Costs (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension
Weighted Average Assumptions Used to Determine Benefit Obligation
Discount Rate	5.39%	5.70%
Rate of Compensation Increase	3.52%	3.58%
Weighted Average Assumptions Used to Determine Net Periodic Benefit Costs
Discount Rate	5.70%	3.28%	2.87%
Expected Long-Term Return on Plan Assets	6.83%	6.00%	6.50%
Rate of Compensation Increase	3.58%	3.58%	3.62%
Postretirement Health and Life
Weighted Average Assumptions Used to Determine Benefit Obligation
Discount Rate	5.42%	5.68%
Health Care Trend Rates
Trend Rate	7.00%	6.50%
Ultimate Trend Rate	5.00%	5.00%
Year Ultimate Trend Rate Effective	2038	2038
Weighted Average Assumptions Used to Determine Net Periodic Benefit Costs
Discount Rate	5.89%	3.09%	2.70%
Expected Long-Term Return on Plan Assets	6.33%	5.41%	5.85%

Operations and Significant Accounting Policies - Narrative (Details)	3 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) segment customer state unit entity MW	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Other Income (Expense) - Other [Line Items]
Number of reportable segments \| segment		2
Impairment of long-lived assets held-for-use		$ 0	$ 0	$ 0
Residual value of leased asset		3,000,000
Contract asset - noncurrent		18,500,000	21,000,000.0
Capitalized contract cost, amortization		2,400,000	2,400,000
Net Loss Attributable to Non-Controlling Interest		$ 68,200,000	58,000,000.0	$ 31,400,000
Immaterial Out-of-Period Adjustment
Other Income (Expense) - Other [Line Items]
Net Loss Attributable to Non-Controlling Interest	$ 5,700,000		3,600,000
Large Power Customers \| Customer Concentration Risk
Other Income (Expense) - Other [Line Items]
Number of customers \| customer		8
Receivables from large power customers		$ 11,200,000	$ 11,300,000
Number of entities \| entity		2
Large Power Customers \| Customer Concentration Risk \| Largest Customer \| Consolidated Operating Revenue
Other Income (Expense) - Other [Line Items]
Concentration risk		21.00%	26.00%	28.00%
Nemadji Trail Energy Center
Other Income (Expense) - Other [Line Items]
Estimated capital expenditures, including past expenditures		$ 700,000,000
Boswell Unit 3 \| 2021 Integrated Resource Plan \| MPUC
Other Income (Expense) - Other [Line Items]
Net book value		220,000,000
Boswell Unit 4 \| 2021 Integrated Resource Plan \| MPUC
Other Income (Expense) - Other [Line Items]
Net book value		$ 420,000,000
Glen Ullin Energy Center
Other Income (Expense) - Other [Line Items]
Generating capacity subject to tax equity financing \| MW		106
South Peak
Other Income (Expense) - Other [Line Items]
Generating capacity subject to tax equity financing \| MW		80
Diamond Spring
Other Income (Expense) - Other [Line Items]
Generating capacity subject to tax equity financing \| MW		303
Caddo
Other Income (Expense) - Other [Line Items]
Generating capacity subject to tax equity financing \| MW		303
New Energy Solar Energy Facilities
Other Income (Expense) - Other [Line Items]
Generating capacity subject to tax equity financing \| MW		14
Square Butte PPA \| Square Butte Coal-fired Unit
Other Income (Expense) - Other [Line Items]
Output being purchased (MW) \| MW		227.5
Square Butte \| Square Butte PPA \| Square Butte Coal-fired Unit
Other Income (Expense) - Other [Line Items]
Generating capacity counterparty owned (MW) \| MW		455
Natural Gas-Fired \| Nemadji Trail Energy Center
Other Income (Expense) - Other [Line Items]
Generating capacity jointly owned (MW) \| MW		600
Nobles 2
Other Income (Expense) - Other [Line Items]
Ownership percentage		49.00%
Generating capacity subject to tax equity financing \| MW		250
Minnesota Power \| Square Butte \| Square Butte PPA \| Square Butte Coal-fired Unit
Other Income (Expense) - Other [Line Items]
Expected output entitlement		50.00%
Minnesota Power \| Wind Turbine Generators \| Tenaska \| Nobles 2 PPA
Other Income (Expense) - Other [Line Items]
Generating capacity counterparty owned (MW) \| MW		250
Contract term		20 years
South Shore Energy \| Nemadji Trail Energy Center
Other Income (Expense) - Other [Line Items]
Capital cost spent to date		$ 9,000,000
South Shore Energy \| Natural Gas-Fired \| Nemadji Trail Energy Center
Other Income (Expense) - Other [Line Items]
Expected output entitlement		20.00%
New Energy
Other Income (Expense) - Other [Line Items]
Discount rate - input for goodwill analysis		14.00%
Terminal growth rate - input for goodwill analysis		3.50%
Regulated Operations \| Alternative Programs
Other Income (Expense) - Other [Line Items]
Revenue collection period following the annual period it is recognized		24 months
Regulated Operations \| Municipal Customers \| Wholesale Electric Service \| Long-term Contract with Customer \| Municipal
Other Income (Expense) - Other [Line Items]
Number of customers \| customer		14
Length of notice required to terminate contract		3 years
Regulated Operations \| Industrial Customers \| Long-term Contract with Customer \| Industrial \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Other Income (Expense) - Other [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period		3 years
Revenue, remaining performance obligation, amount		$ 62,000,000
Regulated Operations \| Industrial Customers \| Long-term Contract with Customer \| Industrial \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01
Other Income (Expense) - Other [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period		1 year
Revenue, remaining performance obligation, amount		$ 15,000,000
Regulated Operations \| Industrial Customers \| Long-term Contract with Customer \| Industrial \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01
Other Income (Expense) - Other [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period
Revenue, remaining performance obligation, amount		$ 12,000,000
Regulated Operations \| Industrial Customers \| Retail Electric Service \| Industrial
Other Income (Expense) - Other [Line Items]
Percentage of total regulated utility k wh sales		55.00%
Regulated Operations \| Industrial Customers \| Retail Electric Service \| Long-term Contract with Customer \| Industrial
Other Income (Expense) - Other [Line Items]
Large power customer contracts \| customer		8
Contract serving requirement \| MW		10
Length of notice required to terminate contract		4 years
Regulated Operations \| Other Power Supplier Customers \| Sale of Energy under PSA \| Long-term Contract with Customer \| Other Power Suppliers
Other Income (Expense) - Other [Line Items]
Number of customers \| customer		1
Regulated Operations \| Large Power Customers \| Customer Concentration Risk \| Largest Customer \| Consolidated Operating Revenue
Other Income (Expense) - Other [Line Items]
Concentration risk		32.00%	32.00%	32.00%
ALLETE Clean Energy
Other Income (Expense) - Other [Line Items]
Number of states operated in \| state		7
Energy generation owned (MW) \| MW		1,200
Corporate and Other \| BNI Energy
Other Income (Expense) - Other [Line Items]
Number of customers \| unit		2
Corporate and Other \| BNI Energy \| Square Butte Coal-fired Unit
Other Income (Expense) - Other [Line Items]
Number of customers \| unit		1
Electric Rates \| Regulated Operations \| Minnesota Power \| Municipal Customers
Other Income (Expense) - Other [Line Items]
Number of customers \| customer		14
Electric Rates \| Retail Customers \| Regulated Operations \| Minnesota Power
Other Income (Expense) - Other [Line Items]
Number of customers \| customer		150,000
Electric Rates \| Retail Customers \| Regulated Operations \| SWL&P
Other Income (Expense) - Other [Line Items]
Number of customers \| customer		15,000
Natural Gas \| Retail Customers \| Regulated Operations \| SWL&P
Other Income (Expense) - Other [Line Items]
Number of customers \| customer		13,000
Water \| Retail Customers \| Regulated Operations \| SWL&P
Other Income (Expense) - Other [Line Items]
Number of customers \| customer		10,000

Common Stock and Earnings Per Share (Tables)

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Summary of Common Stock


Summary of Common Stock	Shares	Equity
	Thousands	Millions
Balance as of December 31, 2020	52,085	$1,460.9
Employee Stock Purchase Plan	17	0.8
Invest Direct	263	17.5
Share-Based Compensation	73	6.5

Equity Issuance Program	782	51.0




Balance as of December 31, 2021	53,220	1,536.7
Employee Stock Purchase Plan	11	0.9
Invest Direct	244	14.9
Share-Based Compensation	82	5.3

Equity Issuance	3,680	223.7




Balance as of December 31, 2022	57,237	1,781.5
Employee Stock Purchase Plan	16	0.8
Invest Direct	232	13.3
Share-Based Compensation	76	8.1





Balance as of December 31, 2023	57,561	$1,803.7

Reconciliation of Basic and Diluted Earnings Per Share


Reconciliation of Basic and Diluted
Earnings Per Share		Dilutive
Year Ended December 31	Basic	Securities	Diluted
Millions Except Per Share Amounts
2023
Net Income Attributable to ALLETE	$247.1		$247.1
Average Common Shares	57.3	0.1	57.4
Earnings Per Share	$4.31		$4.30

2022
Net Income Attributable to ALLETE	$189.3		$189.3
Average Common Shares	55.9	0.1	56.0
Earnings Per Share	$3.38		$3.38

2021
Net Income Attributable to ALLETE	$169.2		$169.2
Average Common Shares	52.4	0.1	52.5
Earnings Per Share	$3.23		$3.23

Commitments, Guarantees and Contingencies - Environmental Matters (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)
Coal Combustion Residuals \| Minnesota Power
Environmental Matters [Line Items]
Expected period for costs of compliance	12 years
Coal Combustion Residuals \| Minimum \| Minnesota Power
Environmental Matters [Line Items]
Estimated costs of compliance	$ 65
Coal Combustion Residuals \| Maximum \| Minnesota Power
Environmental Matters [Line Items]
Estimated costs of compliance	120
Manufactured Gas Plant \| SWL&P \| Superior, WI
Environmental Matters [Line Items]
Environmental remediation liability	$ 1

Income Tax Expense - NOL and Tax Credit Carryforwards (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Federal
NOL and Tax Credit Carryforwards [Line Items]
Tax Credit Carryforwards	$ 480,400,000	$ 464,500,000
Federal Capital Loss Carryforwards	0	35,100,000
Valuation allowance	0
State
NOL and Tax Credit Carryforwards [Line Items]
Tax Credit Carryforwards	21,500,000	24,500,000
NOL Carryforwards	280,900,000	323,000,000.0
State Capital Loss Carryforwards	0	83,200,000
Valuation allowance	55,400,000	59,600,000
Valuation allowance	$ 10,500,000
State \| Capital Loss Carryforward
NOL and Tax Credit Carryforwards [Line Items]
Valuation allowance		$ 58,700,000

Equity Investments - Investments (Details) - USD ($) $ in Millions	3 Months Ended												12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Equity Method Investments [Roll Forward]
Equity Investment Beginning Balance				$ 322.7									$ 322.7
Cash Investments													8.2	$ 5.9	$ 17.6
Equity Earnings													21.7	18.7	20.0
Equity Investment Ending Balance	$ 331.2				$ 322.7								331.2	322.7
Balance Sheet Data
Current Assets	468.1				718.0								468.1	718.0
Total Assets	6,656.4				6,845.6								6,656.4	6,845.6
Current Liabilities	377.6				716.2								377.6	716.2
Members’ Equity	3,406.6				3,348.3				$ 2,937.5				3,406.6	3,348.3	2,937.5
Total Liabilities and Members’ Equity	6,656.4				6,845.6								6,656.4	6,845.6
Income Statement Data
Operating Revenue	402.7	$ 378.8	$ 533.4	564.9	425.8	$ 388.3	$ 373.1	$ 383.5	399.0	$ 345.4	$ 335.6	$ 339.2	1,879.8	1,570.7	1,419.2
Net Income													178.9	131.3	137.8
Net Loss Attributable to Non-Controlling Interest													(68.2)	(58.0)	(31.4)
ATC
Balance Sheet Data
Current Assets	115.2				89.6								115.2	89.6
Non-Current Assets	6,337.0				5,997.8								6,337.0	5,997.8
Total Assets	6,452.2				6,087.4								6,452.2	6,087.4
Current Liabilities	495.9				511.9								495.9	511.9
Long-Term Debt	2,736.0				2,613.0								2,736.0	2,613.0
Other Non-Current Liabilities	585.2				485.8								585.2	485.8
Members’ Equity	2,635.1				2,476.7								2,635.1	2,476.7
Total Liabilities and Members’ Equity	6,452.2				6,087.4								6,452.2	6,087.4
Income Statement Data
Operating Revenue													818.9	751.2	754.8
Operating Expense													407.6	381.5	376.2
Other Expense													131.7	122.9	113.9
Net Income													279.6	246.8	264.7
Nobles 2
Income Statement Data
Net Loss Attributable to Non-Controlling Interest													10.2
ATC
Equity Method Investments [Roll Forward]
Equity Investment Beginning Balance				165.4				$ 154.5					165.4	154.5
Cash Investments													8.2	5.9
Equity Earnings													23.1	19.3	21.3
Distributed Earnings													(18.3)	(15.5)
Amortization of the Remeasurement of Deferred Income Taxes													1.3	1.2
Equity Investment Ending Balance	179.7				165.4				$ 154.5				179.7	165.4	$ 154.5
Nobles 2
Equity Method Investments [Roll Forward]
Equity Investment Beginning Balance				$ 157.3									157.3
Equity Earnings													(1.4)
Distributed Earnings													(4.4)
Equity Investment Ending Balance	$ 151.5				$ 157.3								$ 151.5	$ 157.3

Jointly-Owned Facilities and Assets

12 Months Ended

Dec. 31, 2023

Jointly-Owned Facilities and Assets [Abstract]

Jointly-Owned Facilities and Assets

JOINTLY-OWNED FACILITIES AND ASSETS

Boswell Unit 4. Minnesota Power owns 80 percent of the 585 MW Boswell Unit 4. While Minnesota Power operates the plant, certain decisions about the operations of Boswell Unit 4 are subject to the oversight of a committee on which it and WPPI Energy, the owner of the remaining 20 percent, have equal representation and voting rights. Each owner must provide its own financing and is obligated to its ownership share of operating costs. Minnesota Power’s share of operating expenses for Boswell Unit 4 is included in Operating Expenses on the Consolidated Statement of Income.

NOTE 3. JOINTLY-OWNED FACILITIES AND ASSETS (Continued)

Minnesota Power’s investments in jointly-owned facilities and assets and the related ownership percentages are as follows:


Regulated Utility Plant	Plant in Service	Accumulated Depreciation	Construction Work in Progress	% Ownership
Millions
As of December 31, 2023
Boswell Unit 4	$725.9	$369.8	$2.8	80
Transmission Assets	101.0	23.6	—	9.3 - 14.7
Total	$826.9	$393.4	$2.8
As of December 31, 2022
Boswell Unit 4	$712.0	$340.1	$3.3	80
Transmission Assets	101.0	21.1	—	9.3 - 14.7
Total	$813.0	$361.2	$3.3

Nemadji Trail Energy Center. South Shore Energy, ALLETE’s non-rate regulated, Wisconsin subsidiary, is developing NTEC, an approximately 600 MW proposed combined-cycle natural gas-fired generating facility to be built in Superior, Wisconsin, which will be jointly owned by Dairyland Power Cooperative, Basin and South Shore Energy. Minnesota Power is expected to purchase approximately 20 percent of the facility's output starting in 2028 pursuant to a capacity dedication agreement. Construction of NTEC is subject to obtaining additional permits from local, state and federal authorities. The total project cost is estimated to be approximately $700 million, of which South Shore Energy will be responsible for approximately 20 percent. South Shore Energy’s portion of NTEC project costs incurred through December 31, 2023, is approximately $9 million.

Pension and Other Postretirement Benefit Plans - Recurring Fair Value Measures, Activity in Level 3 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Pension
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	$ 568.6	$ 745.7
Fair Value, End of Year	589.0	568.6
Pension \| Level 3
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	22.4
Fair Value, End of Year	18.9	22.4
Pension \| Real Estate
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	22.4
Fair Value, End of Year	18.9	22.4
Pension \| Real Estate \| Level 3
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	22.4	21.6
Actual Return on Plan Assets	(3.1)	1.0
Purchases, Sales, and Settlements – Net	(0.4)	(0.2)
Fair Value, End of Year	18.9	22.4
Postretirement Health and Life
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	162.6	201.8
Fair Value, End of Year	173.8	162.6
Postretirement Health and Life \| Level 3
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	0.0
Fair Value, End of Year	0.0	0.0
Postretirement Health and Life \| Private Equity \| Level 3
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	$ 0.0	2.0
Actual Return on Plan Assets		(1.5)
Purchases, Sales, and Settlements – Net		(0.5)
Fair Value, End of Year		$ 0.0

- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

+ References + Details

Pension and Other Postretirement Benefit Plans - Components of Net Periodic Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service Cost	$ 6.5	$ 9.3	$ 11.0
Interest Cost	40.5	27.2	24.6
Expected Return on Plan Assets	(43.8)	(41.5)	(43.4)
Amortization of (Gain) Loss	5.8	11.4	18.8
Amortization of Prior Service Credit	(0.1)	(0.1)	(0.2)
Net Pension Cost	8.9	6.3	10.8
Postretirement Health and Life Obligation and Funded Status
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service Cost	2.0	3.0	3.6
Interest Cost	5.6	4.4	4.4
Expected Return on Plan Assets	(11.4)	(9.6)	(9.9)
Amortization of (Gain) Loss	(2.7)	0.4	3.0
Amortization of Prior Service Credit	(8.5)	(7.5)	(7.6)
Net Pension Cost	$ (15.0)	$ (9.3)	$ (6.5)

Income Tax Expense

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Tax Expense

INCOME TAX EXPENSE


Income Tax Expense
Year Ended December 31	2023	2022	2021
Millions
Current Income Tax Expense (a)
Federal	$9.4	$1.2	—
State	0.9	6.1	—
Total Current Income Tax Expense	$10.3	$7.3	—
Deferred Income Tax Expense (Benefit)
Federal (b)	$(6.0)	$(32.8)	$(37.2)

State (c)	24.0	(5.2)	10.8

Investment Tax Credit Amortization	(0.4)	(0.5)	(0.5)
Total Deferred Income Tax Expense (Benefit)	$17.6	$(38.5)	$(26.9)
Total Income Tax Expense (Benefit)	$27.9	$(31.2)	$(26.9)

(c)For the year ended December 31, 2022, the state impact includes the benefit of deferred repricing as a result of the New Energy acquisition.


Reconciliation of Taxes from Federal Statutory
Rate to Total Income Tax Expense
Year Ended December 31	2023		2022		2021
Millions
Income Before Non-Controlling Interest and Income Taxes	$206.8		$100.1		$110.9
Statutory Federal Income Tax Rate	21	%	21	%	21	%
Income Taxes Computed at Statutory Federal Rate	$43.4		$21.0		$23.3
Increase (Decrease) in Tax Due to:
State Income Taxes – Net of Federal Income Tax Benefit	19.7		8.6		8.6
Deferred Revaluation – Net of Federal Income Tax Benefit	—		(7.9)		—


Production Tax Credits (a)	(31.6)		(50.7)		(53.5)
Investment Tax Credits (a)	(5.8)		(4.1)		—
Regulatory Differences – Excess Deferred Tax Benefit	(9.9)		(9.1)		(9.5)


Non-Controlling Interest	13.3		11.2		6.3
AFUDC - Equity	(1.3)		(1.1)		(1.0)
Other	0.1		0.9		(1.1)
Total Income Tax Expense (Benefit)	$27.9		$(31.2)		$(26.9)

(a)For the year ended December 31, 2023, the credits are presented net of any estimated discount on the sale of certain credits.

The effective tax rate was an expense of 13.5 percent for 2023 (benefit of 31.2 percent for 2022; benefit of 24.3 percent for 2021). The 2023, 2022 and 2021 effective tax rates were primarily impacted by production tax credits and non-controlling interests in subsidiaries.

NOTE 11. INCOME TAX EXPENSE (Continued)


Deferred Income Tax Assets and Liabilities
As of December 31	2023	2022
Millions
Deferred Income Tax Assets
Employee Benefits and Compensation	$29.3	$46.4
Property-Related	58.1	61.9
NOL Carryforwards	13.0	16.7
Capital Loss Carryforwards	2.1	13.1
Tax Credit Carryforwards	557.4	548.7
Power Sales Agreements	9.0	13.7
Regulatory Liabilities	89.0	95.5
Other	8.7	28.1
Gross Deferred Income Tax Assets	766.6	824.1
Deferred Income Tax Asset Valuation Allowance	(58.0)	(60.2)
Total Deferred Income Tax Assets	$708.6	$763.9
Deferred Income Tax Liabilities
Deferred Gain	$7.9	$7.9
Property-Related	632.0	661.7
Regulatory Asset for Benefit Obligations	48.1	57.7
Unamortized Investment Tax Credits	29.6	30.0
Partnership Basis Differences	156.5	126.0
Fuel Adjustment Clause	1.9	10.7
Regulatory Assets	25.3	28.0

Total Deferred Income Tax Liabilities	$901.3	$922.0
Net Deferred Income Taxes (a)	$192.7	$158.1

(a)Recorded as a net Deferred Income Tax liability on the Consolidated Balance Sheet.


NOL and Tax Credit Carryforwards
As of December 31	2023	2022
Millions

Federal Tax Credit Carryforwards	$480.4	$464.5
Federal Capital Loss Carryforwards (a)	—	$35.1
State NOL Carryforwards (a)	$280.9	$323.0
State Tax Credit Carryforwards (b)	$21.5	$24.5
State Capital Loss Carryforwards (a)	—	$83.2

(a)Pre-tax amounts; state NOL carryforwards net of a $10.5 million valuation allowance and state capital loss carryforwards net of a $58.7 million valuation allowance.

(b)Net of a $55.4 million valuation allowance as of December 31, 2023 ($59.6 million as of December 31, 2022).

The federal tax credit carryforward periods expire between 2034 and 2043. We expect to fully utilize the tax credit carryforwards; therefore, no federal valuation allowance has been recognized as of December 31, 2023. The apportioned state NOL, capital loss and tax credit carryforward periods expire between 2024 and 2045. We have established a valuation allowance against certain state NOL, capital loss and tax credits that we do not expect to utilize before their expiration.

NOTE 11. INCOME TAX EXPENSE (Continued)


Gross Unrecognized Income Tax Benefits	2023	2022	2021
Millions
Balance at January 1	$1.3	$1.3	$1.4


Reductions for Tax Positions Related to Prior Years	(0.2)	—	(0.1)


Balance as of December 31	$1.1	$1.3	$1.3

Unrecognized tax benefits are the differences between a tax position taken or expected to be taken in a tax return and the benefit recognized and measured pursuant to the “more-likely-than-not” criteria. The unrecognized tax benefit balance includes permanent tax positions which, if recognized, would affect the annual effective income tax rate. In addition, the unrecognized tax benefit balance includes temporary tax positions for which the ultimate deductibility is highly certain but for which there is uncertainty about the timing of such deductibility. A change in the period of deductibility would not affect the effective tax rate but would accelerate the payment of cash to the taxing authority to an earlier period. The gross unrecognized tax benefits as of December 31, 2023, included $0.6 million of net unrecognized tax benefits which, if recognized, would affect the annual effective income tax rate.

As of December 31, 2023, we had accrued interest of $0.1 million (none as of December 31, 2022, and 2021) related to unrecognized tax benefits included on the Consolidated Balance Sheet due to our NOL carryforwards. We classify interest related to unrecognized tax benefits as interest expense and tax-related penalties in operating expenses on the Consolidated Statement of Income. Interest expense related to unrecognized tax benefits on the Consolidated Statement of Income was immaterial in 2023, 2022 and 2021. There were no penalties recognized in 2023, 2022 or 2021. The unrecognized tax benefit amounts have been presented as an increase to the net deferred tax liability on the Consolidated Balance Sheet.

No material changes to unrecognized tax benefits are expected during the next 12 months.

ALLETE and its subsidiaries file a consolidated federal income tax return as well as combined and separate state income tax returns in various jurisdictions. ALLETE is currently under examination by the state of Minnesota for the tax years 2020 through 2022. ALLETE has no open federal audits, and is no longer subject to federal examination for years before 2020 or state examination for years before 2019. Additionally, the statute of limitations related to the federal tax credit carryforwards will remain open until those credits are utilized in subsequent returns.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
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+ Details

Employee Stock and Incentive Plans - Performance Shares and Restricted Stock Units (Details) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Performance Shares
Number of Shares
As of January 1	60,489	80,661	85,284
Granted (in shares)	54,039	37,731	33,304
Awarded (in shares)	0	0	0
Unearned Grant Award (in shares)	0	(50,524)	(33,375)
Forfeited (in shares)	(3,030)	(7,379)	(4,552)
As of December 31	111,498	60,489	80,661
Weighted- Average Grant Date Fair Value
As of January 1	$ 69.62	$ 75.80	$ 80.73
Granted	63.50	67.22	73.25
Awarded	0	0	0
Unearned Grant Award	0	77.49	86.09
Forfeited	67.60	71.00	74.05
As of December 31	$ 66.71	$ 69.62	$ 75.80
Restricted Stock Units
Number of Shares
As of January 1	33,564	28,141	37,482
Granted (in shares)	21,200	15,477	16,251
Awarded (in shares)	(9,631)	(7,396)	(23,631)
Forfeited (in shares)	(1,389)	(2,658)	(1,961)
As of December 31	43,744	33,564	28,141
Weighted- Average Grant Date Fair Value
As of January 1	$ 68.80	$ 73.16	$ 77.64
Granted	61.16	63.70	64.97
Awarded	81.91	75.55	74.53
Forfeited	63.46	66.44	74.52
As of December 31	$ 62.38	$ 68.80	$ 73.16

Employee Stock and Incentive Plans

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Employee Stock and Incentive Plans

EMPLOYEE STOCK AND INCENTIVE PLANS

Employee Stock Ownership Plan. We sponsor an ESOP within the RSOP. Eligible employees may contribute to the RSOP plan as of their date of hire. The dividends received by the ESOP are distributed to participants. Dividends on allocated ESOP shares are recorded as a reduction of retained earnings. ESOP employer allocations are funded with contributions paid in either cash or the issuance of ALLETE common stock at the Company’s discretion. We record compensation expense equal to the cash or current market price of stock contributed. ESOP compensation expense was $13.7 million in 2023 ($12.0 million in 2022; $11.5 million in 2021).

According to the accounting standards for stock compensation, unallocated shares of ALLETE common stock held and purchased by the ESOP were treated as unearned ESOP shares and not considered outstanding for earnings per share computations. All ESOP shares have been allocated to participants as of December 31, 2023, 2022 and 2021.

Stock-Based Compensation.

Stock Incentive Plan. Under our Executive Long-Term Incentive Compensation Plan (Executive Plan), share-based awards may be issued to key employees through a broad range of methods, including non-qualified and incentive stock options, performance shares, performance units, restricted stock, restricted stock units, stock appreciation rights and other awards. There are 0.7 million shares of ALLETE common stock reserved for issuance under the Executive Plan, of which 0.6 million of these shares remain available for issuance as of December 31, 2023.

NOTE 13. EMPLOYEE STOCK AND INCENTIVE PLANS (Continued)

Stock-Based Compensation (Continued)

The following types of share-based awards were outstanding in 2023, 2022 or 2021:

Performance Shares. Under the performance share awards, the number of shares earned is contingent upon attaining specific market and performance goals over a three-year performance period. Market goals are measured by total shareholder return relative to a group of peer companies while performance goals are measured by earnings per share growth. In the case of qualified retirement, death, or disability during a performance period, a pro rata portion of the award will be earned at the conclusion of the performance period based on the market goals achieved. In the case of termination of employment for any reason other than qualified retirement, death, or disability, no award will be earned. If there is a change in control, a pro rata portion of the award will be paid based on the greater of actual performance up to the date of the change in control or target performance. The fair value of these awards incorporates the probability of meeting the total shareholder return goals. Compensation cost is recognized over the three-year performance period based on our estimate of the number of shares which will be earned by the award recipients.

Restricted Stock Units. Under the restricted stock unit awards, shares for participants eligible for retirement vest monthly over a three-year period. For participants not eligible for retirement, shares vest at the end of the three-year period. In the case of qualified retirement, death or disability, a pro rata portion of the award will be earned. In the case of termination of employment for any reason other than qualified retirement, death or disability, no award will be earned. If there is a change in control, a pro rata portion of the award will be earned. The fair value of these awards is equal to the grant date fair value. Compensation cost is recognized over the three-year vesting period based on our estimate of the number of shares which will be earned by the award recipients.

Employee Stock Purchase Plan (ESPP). Under our ESPP, eligible employees may purchase ALLETE common stock at a 5 percent discount from the market price; we are not required to apply fair value accounting to these awards as the discount is not greater than 5 percent.

RSOP. The RSOP is a contributory defined contribution plan subject to the provisions of the Employee Retirement Income Security Act of 1974, as amended, and qualifies as an employee stock ownership plan and profit sharing plan. The RSOP provides eligible employees an opportunity to save for retirement.

The following share-based compensation expense amounts were recognized in our Consolidated Statement of Income for the periods presented.


Share-Based Compensation Expense
Year Ended December 31	2023	2022	2021
Millions

Performance Shares	$3.1	$0.7	$2.0
Restricted Stock Units	0.8	0.9	1.0
Total Share-Based Compensation Expense	$3.9	$1.6	$3.0
Income Tax Benefit	$1.1	$0.5	$0.9

There were no capitalized share-based compensation costs during the years ended December 31, 2023, 2022 or 2021.

As of December 31, 2023, the total unrecognized compensation cost for the performance share awards and restricted stock units not yet recognized in our Consolidated Statement of Income was $2.6 million and $0.8 million, respectively. These amounts are expected to be recognized over a weighted-average period of 1.7 years and 1.7 years, respectively.

NOTE 13. EMPLOYEE STOCK AND INCENTIVE PLANS (Continued)

Stock-Based Compensation (Continued)

Performance Shares. The following table presents information regarding our non-vested performance shares.


	2023		2022		2021
	Number of Shares	Weighted- Average Grant Date Fair Value	Number of Shares	Weighted- Average Grant Date Fair Value	Number of Shares	Weighted- Average Grant Date Fair Value
Non-vested as of January 1	60,489	$69.62	80,661	$75.80	85,284	$80.73
Granted (a)	54,039	$63.50	37,731	$67.22	33,304	$73.25
Awarded	—	—	—	—	—	—
Unearned Grant Award	—	—	(50,524)	$77.49	(33,375)	$86.09
Forfeited	(3,030)	$67.60	(7,379)	$71.00	(4,552)	$74.05
Non-vested as of December 31	111,498	$66.71	60,489	$69.62	80,661	$75.80

(a) Shares granted include accrued dividends.

There were approximately 61,900 performance shares granted in January 2024 for the three-year performance period ending in 2026. The ultimate issuance is contingent upon the attainment of certain goals of ALLETE during the performance periods. The grant date fair value of the performance shares granted was $4.0 million. There were approximately 46,700 performance shares awarded in February 2024. The grant date fair value of the shares awarded was $3.3 million.

Restricted Stock Units. The following table presents information regarding our available restricted stock units.


	2023		2022		2021
	Number of Shares	Weighted- Average Grant Date Fair Value	Number of Shares	Weighted- Average Grant Date Fair Value	Number of Shares	Weighted- Average Grant Date Fair Value
Available as of January 1	33,564	$68.80	28,141	$73.16	37,482	$77.64
Granted (a)	21,200	$61.16	15,477	$63.70	16,251	$64.97
Awarded	(9,631)	$81.91	(7,396)	$75.55	(23,631)	$74.53
Forfeited	(1,389)	$63.46	(2,658)	$66.44	(1,961)	$74.52
Available as of December 31	43,744	$62.38	33,564	$68.80	28,141	$73.16

(a) Shares granted include accrued dividends.

There were approximately 24,300 restricted stock units granted in January 2024 for the vesting period ending in 2026. The grant date fair value of the restricted stock units granted was $1.4 million. There were approximately 11,200 restricted stock units awarded in February 2024. The grant date fair value of the shares awarded was $0.7 million.

Pension and Other Postretirement Benefit Plans - Unrecognized Postretirement Health and Life Costs (Details) - Postretirement Health and Life Obligation and Funded Status - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net Gain	$ (24.8)	$ (9.2)
Prior Service Credit	(33.8)	(13.2)
Total Unrecognized Postretirement Health and Life Cost	$ (58.6)	$ (22.4)

Commitments, Guarantees and Contingencies - Minimum Payments for Certain Long-Term Commitments (Details) $ in Millions	Dec. 31, 2023 USD ($)
Capital Purchase Obligations
Minimum Annual Payments for Certain Long-Term Commitments [Line Items]
2024	$ 73.9
2025	1.6
2026	9.9
2027	38.1
2028	0.0
Thereafter	10.5
Easements
Minimum Annual Payments for Certain Long-Term Commitments [Line Items]
2024	8.0
2025	8.1
2026	8.1
2027	8.2
2028	8.4
Thereafter	217.7
PPAs
Minimum Annual Payments for Certain Long-Term Commitments [Line Items]
2024	140.7
2025	133.8
2026	136.6
2027	125.7
2028	132.4
Thereafter	937.5
Other Purchase Obligations
Minimum Annual Payments for Certain Long-Term Commitments [Line Items]
2024	42.9
2025	0.0
2026	0.0
2027	0.0
2028	0.0
Thereafter	$ 0.0

Common Stock and Earnings Per Share - Narrative (Details) - USD ($) $ in Millions		12 Months Ended
	Apr. 05, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Summary of Common Stock [Line Items]
Equity Issuance (in shares)	3,700,000
Common Stock Issued	$ 224.0			$ 51.0
Common Stock
Summary of Common Stock [Line Items]
Equity issuance program shares authorized (in shares)					13,600,000
Equity issuance program shares available for issuance (in shares)		2,100,000
Equity Issuance Program (in shares)			3,680,000	782,000
Common Stock \| PIE Shares
Summary of Common Stock [Line Items]
Equity Issuance Program (in shares)		0	0	800,000

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Topic 272
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-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483014/272-10-45-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482987/272-10-50-1

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
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-Subparagraph (SX 210.4-08(d))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 13
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
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-Subparagraph (b)
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

- Definition

Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

+ References + Details

Business Segment (Tables)

12 Months Ended

Dec. 31, 2023

Segment Reporting [Abstract]

Schedule of Segment Reporting Information, by Segment


Year Ended December 31	2023	2022	2021
Millions
Operating Revenue
Residential	$165.7	$175.9	$160.8
Commercial	184.6	187.2	168.6
Municipal	33.4	40.2	52.0
Industrial	593.6	589.0	565.5
Other Power Suppliers	146.1	165.8	168.7

Other	114.9	101.2	112.3
Total Regulated Operations	1,238.3	1,259.3	1,227.9



ALLETE Clean Energy
Long-term PSA	65.0	77.2	75.5
Sale of Wind Energy Facilities	348.4	33.5	—
Other	5.1	7.6	11.4
Total ALLETE Clean Energy	418.5	118.3	86.9

Corporate and Other
Long-term Contract	101.2	89.2	84.4
Sale of Renewable Development Projects	92.5	73.9	—
Other	29.3	30.0	20.0
Total Corporate and Other	223.0	193.1	104.4
Total Operating Revenue	$1,879.8	$1,570.7	$1,419.2
Net Income Attributable to ALLETE (a)
Regulated Operations	$147.2	$149.9	$129.1


ALLETE Clean Energy (b)	71.7	16.3	26.3


Corporate and Other (c)(d)	28.2	23.1	13.8
Total Net Income Attributable to ALLETE	$247.1	$189.3	$169.2

(a) Includes interest expense and interest income resulting from intercompany loan agreements and allocated to certain subsidiaries. The amounts are eliminated in consolidation.

(b) Net income in 2023 includes a $44.3 million after-tax gain recognized for a favorable arbitration ruling. (See Note 9. Commitments, Guarantees and Contingencies.)


Year Ended December 31	2023	2022	2021
Millions
Depreciation and Amortization
Regulated Operations	$179.2	$171.9	$170.7


ALLETE Clean Energy	57.5	58.6	49.2

Corporate and Other	15.1	11.7	11.8
Total Depreciation and Amortization	$251.8	$242.2	$231.7




Interest Expense (a)
Regulated Operations	$63.9	$58.1	$57.3


ALLETE Clean Energy	0.8	2.3	1.5

Corporate and Other	22.5	19.6	13.2

Eliminations	(6.4)	(4.8)	(2.9)
Total Interest Expense	$80.8	$75.2	$69.1
Equity Earnings
Regulated Operations	$23.1	$19.3	$21.3
Corporate and Other	(1.4)	(0.6)	(1.3)
Total Equity Earnings	$21.7	$18.7	$20.0
Income Tax Expense (Benefit)
Regulated Operations	$22.4	$(10.4)	$(16.6)


ALLETE Clean Energy	2.7	(15.4)	(16.6)

Corporate and Other	2.8	(5.4)	6.3
Total Income Tax Expense (Benefit)	$27.9	$(31.2)	$(26.9)

(a) Includes interest expense resulting from intercompany loan agreements and allocated to certain subsidiaries. The amounts are eliminated in consolidation.


As of December 31	2023	2022
Millions
Assets
Regulated Operations	$4,335.0	$4,291.4


ALLETE Clean Energy	1,594.1	1,873.3


Corporate and Other	727.3	680.9
Total Assets	$6,656.4	$6,845.6
Capital Expenditures
Regulated Operations	$236.3	$158.3


ALLETE Clean Energy	(5.3)	2.2


Corporate and Other	25.0	47.6
Total Capital Expenditures	$256.0	$208.1

Operations and Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Operations and Significant Accounting Policies

OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES

Financial Statement Preparation. References in this report to “we,” “us,” and “our” are to ALLETE and its subsidiaries, collectively. We prepare our financial statements in conformity with GAAP. These principles require management to make informed judgments, best estimates, and assumptions that affect the reported amounts of assets, liabilities, revenue and expenses. Actual results could differ from those estimates. The presentation of certain prior period amounts on the Consolidated Financial Statements have been adjusted for comparative purposes.

Subsequent Events. The Company performed an evaluation of subsequent events for potential recognition and disclosure through the time of the financial statements issuance.

Principles of Consolidation. Our Consolidated Financial Statements include the accounts of ALLETE, all of our majority owned subsidiary companies and variable interest entities of which ALLETE is the primary beneficiary. All material intercompany balances and transactions have been eliminated in consolidation.

Variable Interest Entities. The accounting guidance for “Variable Interest Entities” (VIE) is a consolidation model that considers if a company has a variable interest in a VIE. A VIE is a legal entity that possesses any of the following conditions: the entity’s equity at risk is not sufficient to permit the legal entity to finance its activities without additional subordinated financial support, equity owners are unable to direct the activities that most significantly impact the legal entity’s economic performance (or they possess disproportionate voting rights in relation to the economic interest in the legal entity), or the equity owners lack the obligation to absorb the legal entity’s expected losses or the right to receive the legal entity’s expected residual returns. Entities are required to consolidate a VIE when it is determined that they have a controlling financial interest in a VIE and therefore are the primary beneficiary of that VIE, as defined by the accounting guidance for “Variable Interest Entities.” In determining whether ALLETE is the primary beneficiary of a VIE, management considers whether ALLETE has the power to direct the most significant activities of the VIE and is obligated to absorb losses or receive the expected residual returns that are significant to the VIE. The accounting guidance for VIEs applies to certain ALLETE Clean Energy wind energy facilities, certain New Energy Equity facilities, and our investment in Nobles 2. (See Tax Equity Financing.)

Business Segments. We present two reportable segments: Regulated Operations and ALLETE Clean Energy. Our segments were determined in accordance with the guidance on segment reporting. We measure performance of our operations through budgeting and monitoring of contributions to consolidated net income by each business segment.

Regulated Operations includes our regulated utilities, Minnesota Power and SWL&P, as well as our investment in ATC, a Wisconsin-based regulated utility that owns and maintains electric transmission assets in portions of Wisconsin, Michigan, Minnesota and Illinois. Minnesota Power provides regulated utility electric service in northeastern Minnesota to approximately 150,000 retail customers. Minnesota Power also has 14 non-affiliated municipal customers in Minnesota. SWL&P is a Wisconsin utility and a wholesale customer of Minnesota Power. SWL&P provides regulated utility electric, natural gas and water service in northwestern Wisconsin to approximately 15,000 electric customers, 13,000 natural gas customers and 10,000 water customers. Our regulated utility operations include retail and wholesale activities under the jurisdiction of state and federal regulatory authorities.

ALLETE Clean Energy focuses on developing, acquiring, and operating clean and renewable energy projects. ALLETE Clean Energy currently owns and operates, in seven states, more than 1,200 MW of nameplate capacity wind energy generation with a majority contracted under PSAs of various durations. In addition, ALLETE Clean Energy also engages in the development of wind energy facilities to operate under long-term PSAs or for sale to others upon completion.

Corporate and Other is comprised of New Energy, our investment in Nobles 2, South Shore Energy, BNI Energy, ALLETE Properties, other business development and corporate expenditures, unallocated interest expense, a small amount of non-rate base generation, land holdings in Minnesota, and earnings on cash and investments.

New Energy is a renewable energy development company with a primary focus on solar and storage facilities while also offering comprehensive operations, maintenance and asset management services.

Our investment in Nobles 2 represents a 49 percent equity interest in Nobles 2, the entity that owns and operates a 250 MW wind energy facility in southwestern Minnesota pursuant to a 20-year PPA with Minnesota Power.

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

South Shore Energy, ALLETE’s non-rate regulated, Wisconsin subsidiary, is developing NTEC, an approximately 600 MW proposed combined-cycle natural gas-fired generating facility to be built in Superior, Wisconsin, which will be jointly owned by Dairyland Power Cooperative, Basin and South Shore Energy. (See Note 3. Jointly-Owned Facilities and Assets.)

BNI Energy mines and sells lignite coal to two North Dakota mine-mouth generating units, one of which is Square Butte. In 2023, Square Butte supplied 50 percent (227.5 MW) of its output to Minnesota Power under long-term contracts. (See Note 9. Commitments, Guarantees and Contingencies.)

ALLETE Properties represents our legacy Florida real estate investment. Our strategy incorporates the possibility of a bulk sale of the entire ALLETE Properties portfolio. Proceeds from a bulk sale would be strategically deployed to support growth at our Regulated Operations and ALLETE Clean Energy. ALLETE Properties continues to pursue sales of individual parcels over time and will continue to maintain key entitlements and infrastructure.

Cash, Cash Equivalents and Restricted Cash. We consider all investments purchased with original maturities of three months or less to be cash equivalents. As of December 31, 2023, and 2022, restricted cash amounts included in Prepayments and Other on the Consolidated Balance Sheet include deposits required under a tax equity financing agreement and collateral deposits required under an ALLETE Clean Energy loan agreement. The restricted cash amounts included in Other Non-Current Assets represent collateral deposits required under an ALLETE Clean Energy loan agreement and PSAs. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Consolidated Balance Sheet that aggregate to the amounts presented in the Consolidated Statement of Cash Flows.


Cash, Cash Equivalents and Restricted Cash
As of December 31	2023	2022	2021
Millions
Cash and Cash Equivalents	$71.9	$36.4	$45.1
Restricted Cash included in Prepayments and Other	5.1	1.5	0.3
Restricted Cash included in Other Non-Current Assets	2.4	2.3	2.3
Cash, Cash Equivalents and Restricted Cash on the Consolidated Statement of Cash Flows	$79.4	$40.2	$47.7

Supplemental Statement of Cash Flow Information.


Consolidated Statement of Cash Flows
Year Ended December 31	2023	2022	2021
Millions
Cash Paid During the Period for Interest – Net of Amounts Capitalized	$80.5	$72.8	$66.8






Cash Paid for Income Taxes	$19.5	$6.0	—
Noncash Investing and Financing Activities
Increase (Decrease) in Accounts Payable for Capital Additions to Property, Plant and Equipment	$2.2	$(9.6)	$(14.0)
Reclassification of Property, Plant and Equipment to Inventory (a)	—	$99.7	—
Reclassification of Redeemable Non-Controlling Interest to Current Liabilities (b)	—	—	$30.6
Capitalized Asset Retirement Costs	$5.8	$11.8	$16.9


AFUDC–Equity	$3.6	$2.7	$2.6

(b)Amount reclassified to Current Liabilities resulting from the exercise of an option to buy out a non-controlling interest.

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

Accounts Receivable. Accounts receivable are reported on the Consolidated Balance Sheet net of an allowance for doubtful accounts. The allowance is based on our evaluation of the receivable portfolio under current conditions, overall portfolio quality, review of specific situations and such other factors that, in our judgment, deserve recognition in estimating losses.


Accounts Receivable
As of December 31	2023	2022
Millions
Trade Accounts Receivable
Billed	$106.8	$107.1
Unbilled	23.8	29.2
Less: Allowance for Doubtful Accounts	1.6	1.6
Total Trade Accounts Receivable	129.0	134.7
Income Taxes Receivable	8.2	3.2
Total Accounts Receivable	$137.2	$137.9

Concentration of Credit Risk. We are subject to concentration of credit risk primarily as a result of accounts receivable. Minnesota Power sells electricity to eight Large Power Customers. Receivables from these customers totaled $11.2 million as of December 31, 2023 ($11.3 million as of December 31, 2022). Minnesota Power does not obtain collateral to support utility receivables, but monitors the credit standing of major customers. In addition, Minnesota Power, as permitted by the MPUC, requires its taconite-producing Large Power Customers to pay weekly for electric usage based on monthly energy usage estimates, which allows us to closely manage collection of amounts due. Minnesota Power’s taconite customers, which are currently owned by two entities at the end of 2023, accounted for 32 percent of Regulated Operations operating revenue and 21 percent of consolidated operating revenue in 2023 (32 percent of Regulated Operations operating revenue and 26 percent of consolidated operating revenue in 2022 and 32 percent of Regulated Operations operating revenue and 28 percent of consolidated operating revenue in 2021).

Long-Term Finance Receivables. Long-term finance receivables relating to our real estate operations are collateralized by property sold, accrue interest at market-based rates and are net of an allowance for doubtful accounts. We assess delinquent finance receivables by comparing the balance of such receivables to the estimated fair value of the collateralized property. If the fair value of the property is less than the finance receivable, we record a reserve for the difference. We estimate fair value based on recent property tax assessed values or current appraisals.

Available-for-Sale Securities. Available-for-sale debt and equity securities are recorded at fair value. Unrealized gains and losses on available-for-sale debt securities are included in accumulated other comprehensive income (loss), net of tax. Unrealized gains and losses on available-for-sale equity securities are recognized in earnings. We use the specific identification method as the basis for determining the cost of securities sold.

Inventories – Net. Inventories are stated at the lower of cost or net realizable value. Inventories in our Regulated Operations segment are carried at an average cost or first-in, first-out basis. Inventories in our ALLETE Clean Energy segment and Corporate and Other businesses are carried at an average cost, first-in, first-out or specific identification basis.


Inventories – Net
As of December 31	2023	2022
Millions
Fuel (a)	$27.2	$33.4
Materials and Supplies	115.7	75.1
Renewable Energy Facilities Under Development (b)	32.5	347.4




Total Inventories – Net	$175.4	$455.9

(a) Fuel consists primarily of coal inventory at Minnesota Power.

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

Property, Plant and Equipment. Property, plant and equipment are recorded at original cost and are reported on the Consolidated Balance Sheet net of accumulated depreciation. Expenditures for additions, significant replacements, improvements and major plant overhauls are capitalized; maintenance and repair costs are expensed as incurred. Gains or losses on property, plant and equipment for Corporate and Other operations are recognized when they are retired or otherwise disposed. When property, plant and equipment in our Regulated Operations and ALLETE Clean Energy segments are retired or otherwise disposed, no gain or loss is recognized in accordance with the accounting standards for component depreciation except for certain circumstances where the retirement is unforeseen or unexpected. Our Regulated Operations capitalize AFUDC, which includes both an interest and equity component. AFUDC represents the cost of both debt and equity funds used to finance utility plant additions during construction periods. AFUDC amounts capitalized are included in rate base and are recovered from customers as the related property is depreciated. Upon MPUC approval of cost recovery, the recognition of AFUDC ceases. (See Note 2. Property, Plant and Equipment.)

Impairment of Long-Lived Assets. We review our long-lived assets for indicators of impairment in accordance with the accounting standards for property, plant and equipment on a quarterly basis. This includes our property, plant and equipment (see Property, Plant and Equipment) and land inventory. Land inventory is accounted for as held for use and is recorded at cost, unless the carrying value is determined not to be recoverable in accordance with the accounting standards for property, plant and equipment, in which case the land inventory is written down to estimated fair value.

In accordance with the accounting standards for property, plant and equipment, if indicators of impairment exist, we test our long lived assets for recoverability by comparing the carrying amount of the asset to the undiscounted future net cash flows expected to be generated by the asset. Cash flows are assessed at the lowest level of identifiable cash flows. The undiscounted future net cash flows are impacted by trends and factors known to us at the time they are calculated, and our expectations related to: management’s best estimate of future use; sales prices; holding period and timing of sales; method of disposition; and future expenditures necessary to maintain the operations.

We continue to monitor changes in the broader energy markets along with wind resource expectations that could indicate impairment at ALLETE Clean Energy wind energy facilities upon contract expirations. A decline in energy prices or lower wind resource expectations could result in a future impairment.

In 2023, 2022 and 2021 there were triggering events identified for our property, plant, and equipment at certain ALLETE Clean Energy wind energy facilities. A recoverability test was performed indicating that the undiscounted cash flows adequately supported the property, plant and equipment book values. As a result, no impairment was recorded in 2023, 2022 or 2021.

Derivatives. ALLETE is exposed to certain risks relating to its business operations that can be managed through the use of derivative instruments. ALLETE may enter into derivative instruments to manage those risks including interest rate risk related to certain variable-rate borrowings, and commodity price and transmission congestion cost risk related to sales to electric customers. We have determined that either these agreements are immaterial to the financial statements, are not derivatives, or, if they are derivatives, the agreements qualify for the normal purchases and normal sales exception to derivative accounting guidance; therefore, derivative accounting is not required.

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

Accounting for Stock-Based Compensation. We apply the fair value recognition guidance for share-based payments. Under this guidance, we recognize stock-based compensation expense for all share-based payments granted, net of an estimated forfeiture rate. (See Note 13. Employee Stock and Incentive Plans.)

Goodwill. Goodwill is the excess of the purchase price (consideration transferred) over the estimated fair value of net assets of acquired businesses. In accordance with GAAP, goodwill is not amortized. Goodwill is assessed annually in the fourth quarter for impairment and whenever an event occurs or circumstances change that would indicate the carrying amount may be impaired. Impairment testing for goodwill is done at the reporting unit level.

As of the date of our annual goodwill impairment testing in 2023, the Company elected to bypass the qualitative assessment of goodwill for impairment, proceeding directly to the two-step impairment test for the New Energy reporting unit. In performing Step 1 of the impairment test, we compared the fair value of the reporting unit to its carrying value including goodwill. If the carrying value including goodwill were to exceed the fair value of a reporting unit, Step 2 of the impairment test would be performed. Step 2 of the impairment test requires the carrying value of goodwill to be reduced to its fair value, if lower, as of the test date.

For Step 1 of the impairment test, we estimated the reporting unit's fair value using standard valuation techniques, including techniques which use estimates of projected future results and cash flows to be generated by the reporting unit. Such techniques generally include a terminal value that utilizes a growth rate on debt-free cash flows. These cash flow valuations involve a number of estimates that require broad assumptions and significant judgment by management regarding future performance. Our annual impairment test in 2023 indicated that the estimated fair value of New Energy exceeded its carrying value, and therefore no impairment existed. The fair value of the reporting unit was determined using a discounted cash flow model, using significant assumptions which included a discount rate of 14 percent, cash flow forecasts through 2028, gross margins, and a terminal growth rate of 3.5 percent.


Other Non-Current Assets
As of December 31	2023	2022
Millions
Contract Assets (a)	$18.5	$21.0



ALLETE Properties	10.8	19.1
Restricted Cash	2.4	2.3
Other Postretirement Benefit Plans	106.3	58.8
Other	124.9	103.1
Total Other Non-Current Assets	$262.9	$204.3


Other Current Liabilities
As of December 31	2023	2022
Millions
Customer Deposits (a)	$7.4	$150.7
PSAs	6.0	6.1


Provision for Interim Rate Refund	—	18.4
Manufactured Gas Plant (b)	0.8	14.7




Other	77.7	61.1
Total Other Current Liabilities	$91.9	$251.0

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)


Other Non-Current Liabilities
As of December 31	2023	2022
Millions
Asset Retirement Obligation (a)	$202.9	$200.4
PSAs	20.9	26.9


Other	40.5	41.7
Total Other Non-Current Liabilities	$264.3	$269.0

Leases. We determine if a contract is, or contains, a lease at inception and recognize a right-of-use asset and lease liability for all leases with a term greater than 12 months. Our right-of-use assets and lease liabilities for operating and finance leases are included in Other Non-Current Assets, Other Current Liabilities and Other Non-Current Liabilities, respectively, in our Consolidated Balance Sheet.

Right-of-use assets represent our right to use an underlying asset for the lease term and lease liabilities represent the obligation to make lease payments arising from the lease. Operating and finance lease right-of-use assets and lease liabilities are recognized at the commencement date based on the estimated present value of lease payments over the lease term. As our leases do not provide an explicit rate, we determine the present value of future lease payments based on our estimated incremental borrowing rate using information available at the lease commencement date. The operating and finance lease right-of-use assets includes lease payments to be made during the lease term and any lease incentives, as applicable.

Our leases may include options to extend or buy out the lease at certain points throughout the term, and if it is reasonably certain at lease commencement that we will exercise that option, we include those rental payments in our calculation of the right-of-use asset and lease liability. Lease and rent expense are recognized on a straight-line basis over the lease term for operating leases. Finance leases recognize interest expense using the interest expense method over the lease term and amortization expense on a straight-line basis over the shorter of the useful life of the asset or the lease term, unless a buy out option is reasonably certain to be exercised, for which we then amortize on a straight-line basis over the useful life of the asset. Leases with a term of 12 months or less are not recognized on the Consolidated Balance Sheet.

The majority of our operating leases are for heavy equipment, vehicles and land with fixed monthly payments which we group into two categories: Vehicles and Equipment; and Land and Other. Our largest operating lease is for the drag line at BNI Energy which includes a termination payment at the end of the lease term if we do not exercise our purchase option. The amount of this payment is $3 million and is included in our calculation of the right-of-use asset and lease liability recorded. None of our other leases contain residual value guarantees. We have one finance lease for heavy equipment which includes a purchase option we are reasonably certain to exercise when the lease terminates.

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

Leases (Continued)

Additional information on the components of lease cost and presentation of cash flows were as follows:


As December 31	2023	2022
Millions
Operating Lease Cost	$5.0	$6.3
Finance Lease Cost	$0.1	—

Other Information:
Operating Cash Flows From Operating Leases	$5.0	$6.3

Financing Cash Flows From Finance Leases	$0.2	—

Additional information related to leases were as follows:


As of December 31	2023		2022
Millions

Balance Sheet Information Related to Leases:
Operating Lease Other Non-Current Assets	$10.7		$12.7
Finance Lease Other Non-Current Assets	2.1		—
Total Lease Right-of-use Assets	$12.8		$12.7

Operating Lease Other Current Liabilities	$3.0		$3.2
Finance Lease Other Current Liabilities	0.4		—
Operating Lease Other Non-Current Liabilities	7.7		9.3
Finance Lease Other Non-Current Liabilities	1.6		—
Total Lease Liabilities	$12.7		$12.5

Income Statement Information Related to Leases:
Operating Lease Rent Expense	$5.0		$6.3

Finance Lease Amortization Expense	0.1		—
Total Operating and Finance Lease Expenses	$5.1		$6.3

Weighted Average Remaining Lease Term (Years):
Operating Leases - Vehicles and Equipment	3		4
Operating Leases - Land and Other	12		16
Finance Leases - Vehicles and Equipment	5		0


Weighted Average Discount Rate:
Operating Leases - Vehicles and Equipment	4.0	%	3.9	%
Operating Leases - Land and Other	5.0	%	3.9	%
Finance Leases - Vehicles and Equipment	5.4	%	—	%

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

Leases (Continued)

Maturities of operating and finance lease liabilities as of December 31, 2023, were as follows:



Millions	Operating	Finance
2024	$3.2	$0.4
2025	3.2	0.4
2026	3.2	0.4
2027	4.1	0.5
2028	0.2	0.6
Thereafter	1.2	—
Total Lease Payments Due	15.1	2.3
Less: Imputed Interest	4.4	0.3
Total Lease Obligations	10.7	2.0
Less: Current Lease Obligations	3.0	0.4
Total Long-term Lease Obligations	$7.7	$1.6

Environmental Liabilities. We review environmental matters on a quarterly basis. Accruals for environmental matters are recorded when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated based on current law and existing technologies. Accruals are adjusted as assessment and remediation efforts progress, or as additional technical or legal information becomes available. Accruals for environmental liabilities are included in the Consolidated Balance Sheet at undiscounted amounts and exclude claims for recoveries from insurance or other third parties. Costs related to environmental contamination treatment and cleanup are expensed unless recoverable in rates from customers. (See Note 9. Commitments, Guarantees and Contingencies.)

Revenue.

Contracts with Customers – Utility includes sales from our regulated operations for generation, transmission and distribution of electric service, and distribution of water and gas services to our customers. Also included is an immaterial amount of regulated steam generation that is used by customers in the production of paper and pulp.

Contracts with Customers – Non-utility includes sales of goods and services to customers from ALLETE Clean Energy and our Corporate and Other businesses.

Other – Non-utility is the non-cash adjustments to revenue recognized by ALLETE Clean Energy for the amortization of differences between contract prices and estimated market prices for PSAs that were assumed during the acquisition of various wind energy facilities.

Revenue Recognition. Revenue is recognized upon transfer of control of promised goods or services to our customers in an amount that reflects the consideration we expect to receive in exchange for those products or services. Revenue is recognized net of allowance for returns and any taxes collected from customers, which are subsequently remitted to the appropriate governmental authorities. We account for shipping and handling activities that occur after the customer obtains control of goods as a cost rather than an additional performance obligation thereby recognizing revenue at time of shipment and accruing shipping and handling costs when control transfers to our customers. We have a right to consideration from our customers in an amount that corresponds directly with the value to the customer for our performance completed to date; therefore, we may recognize revenue in the amount to which we have a right to invoice.

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

Revenue (Continued)

Nature of Revenue Streams

Utility

Residential and Commercial includes sales for electric, gas or water service to customers, who have implied contracts with the utility, under rates governed by the MPUC, PSCW or FERC. Customers are billed on a monthly cycle basis and revenue is recognized for electric, gas or water service delivered during the billing period. Revenue is accrued for service provided but not yet billed at period end. Performance obligations with these customers are satisfied at time of delivery to customer meters and simultaneously consumed.

Municipal includes sales to 14 non-affiliated municipal customers in Minnesota under long-term wholesale electric contracts. One of these wholesale electric contracts include a termination clause requiring a three-year notice to terminate. These contracts have termination dates ranging through 2037, with a majority of contracts expiring in 2029. Performance obligations with these customers are satisfied at the time energy is delivered to an agreed upon municipal substation or meter.

Industrial includes sales recognized from contracts with customers in the taconite mining, paper, pulp and secondary wood products, pipeline and other industries. Industrial sales accounted for approximately 55 percent of total regulated utility kWh sales for the year ended December 31, 2023. Within industrial revenue, Minnesota Power had eight Large Power Customer contracts, each serving requirements of 10 MW or more of customer load as of December 31, 2023. These contracts automatically renew past the contract term unless a four-year written notice is given. Large Power Customer contracts have earliest termination dates ranging from 2027 through 2029. We satisfy our performance obligations for these customers at the time energy is delivered to an agreed upon customer substation. Revenue is accrued for energy provided but not yet billed at period end. Based on current contracts with industrial customers, we expect to recognize minimum revenue for the fixed contract components of approximately $62 million per annum through 2027, $15 million in 2028, and $12 million in total thereafter, which reflects the termination notice period in these contracts. When determining minimum revenue, we assume that customer contracts will continue under the contract renewal provision; however, if long-term contracts are renegotiated and subsequently approved by the MPUC or there are changes within our industrial customer class, these amounts may be impacted. Contracts with customers that contain variable pricing or quantity components are excluded from the expected minimum revenue amounts.

Other Power Suppliers includes the sale of energy under a long-term PSA with one customer as well as MISO market and liquidation sales. The expiration date of this PSA is 2028. Performance obligations with these customers are satisfied at the time energy is delivered to an agreed upon delivery point defined in the contract (generally the MISO pricing node). The current contract with one customer contains variable pricing components that prevent us from estimating future minimum revenue.

Other Revenue includes all remaining individually immaterial revenue streams for Minnesota Power and SWL&P, and is comprised of steam sales to paper and pulp mills, wheeling revenue and other sources. Revenue for steam sales to customers is recognized at the time steam is delivered and simultaneously consumed. Revenue is recognized at the time each performance obligation is satisfied.

CIP Financial Incentive reflects certain revenue that is a result of the achievement of certain objectives for our CIP financial incentives. This revenue is accounted for in accordance with the accounting standards for alternative revenue programs which allow for the recognition of revenue under an alternative revenue program if the program is established by an order from the utility’s regulatory commission, the order allows for automatic adjustment of future rates, the amount of revenue recognized is objectively determinable and probable of recovery, and the revenue will be collected within 24 months following the end of the annual period in which it is recognized. CIP financial incentives are recognized in the period in which the MPUC approves the filing, which is typically mid-year.

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

Revenue (Continued)

Non-utility

ALLETE Clean Energy

Long-term PSA revenue includes all sales recognized under long-term contracts for production, curtailment, capacity and associated renewable energy credits from ALLETE Clean Energy wind energy facilities. Expiration dates of these PSAs range from 2024 through 2039. Performance obligations for these contracts are satisfied at the time energy is delivered to an agreed upon point, or production is curtailed at the request of the customer, at specified prices. Revenue from the sale of renewable energy credits is recognized at the same time the related energy is delivered to the customer when sold to the same party.

Sale of Wind Energy Facility includes revenue recognized for the design, development, construction, and sale of a wind energy facility to a customer. Performance obligations for these types of agreements are satisfied at the time the completed project is transferred to the customer at the commercial operation date. Revenue from the sale of a wind energy facility is recognized at the time of asset transfer.

Other is the non-cash adjustments to revenue recognized by ALLETE Clean Energy for the amortization of differences between contract prices and estimated market prices on assumed PSAs. As part of wind energy facility acquisitions, ALLETE Clean Energy assumed various PSAs that were above or below estimated market prices at the time of acquisition; the resulting differences between contract prices and estimated market prices are amortized to revenue over the remaining PSA term.

Corporate and Other

Long-term Contract encompasses the sale and delivery of coal to customer generation facilities. Revenue is recognized on a monthly basis at the cost of production plus a specified profit per ton of coal delivered to the customer. Coal sales are secured under long-term coal supply agreements extending through 2037. Performance obligations are satisfied during the period as coal is delivered to customer generation facilities.

Sale of Renewable Development Projects includes revenue recognized from development only and development plus construction type projects that are sold to a customer. For development only projects, revenue is recognized at point in time when all required development responsibilities have been completed and ownership has transferred to the customer. For development plus construction, the transaction price is allocated to two performance obligations based upon the standalone selling price of each obligation. Revenue is recognized on the development performance obligation upon satisfying all required development activities and ownership transferring to the customer. Revenue for the construction performance obligation is recognized over time based on construction costs incurred, beginning at notice to proceed through the commercial operation date.

Other primarily includes revenue from BNI Energy unrelated to coal, revenue from New Energy for asset management services and non-development activities, the sale of real estate from ALLETE Properties, and non‑rate base steam generation that is sold for use during production of paper and pulp. Performance obligations are satisfied when control transfers to the customer.

Payment Terms. Payment terms and conditions vary across our businesses. Aside from taconite-producing Large Power Customers, payment terms generally require payment to be made within 15 to 30 days from the end of the period that the service has been rendered. In the case of its taconite-producing Large Power Customers, as permitted by the MPUC, Minnesota Power requires weekly payments for electric usage based on monthly energy usage estimates. These customers receive estimated bills based on Minnesota Power’s estimate of the customers’ energy usage, forecasted energy prices and fuel adjustment clause estimates. Minnesota Power’s taconite-producing Large Power Customers have generally predictable energy usage on a weekly basis and any differences that occur are trued-up the following month. Due to the timing difference of revenue recognition from the timing of invoicing and payment, the taconite-producing Large Power Customers receive credit for the time value of money; however, we have determined that our contracts do not include a significant financing component as the period between when we transfer the service to the customer and when they pay for such service is minimal.

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

Revenue (Continued)

Assets Recognized From the Costs to Obtain a Contract with a Customer. We recognize as an asset the incremental costs of obtaining a contract with a customer if we expect the benefit of those costs to be longer than one year. We expense incremental costs when the asset that would have resulted from capitalizing these costs would have been amortized in one year or less. As of December 31, 2023, we have $18.5 million of assets recognized for costs incurred to obtain contracts with our customers ($21.0 million as of December 31, 2022). Management determined the amount of costs to be recognized as assets based on actual costs incurred and paid to obtain and fulfill these contracts to provide goods and services to our customers. Assets recognized to obtain contracts are amortized on a straight-line basis over the contract term as a non-cash reduction to revenue. We recognized $2.4 million of non-cash amortization for the year ended December 31, 2023 ($2.4 million for the year end December 31, 2022).

Unamortized Discount and Premium on Debt. Discount and premium on debt are deferred and amortized over the terms of the related debt instruments using a method which approximates the effective interest method.

Tax Equity Financings. Certain subsidiaries of ALLETE have entered into tax equity financings that include forming limited liability companies (LLC) with third-party investors for certain wind and solar projects. Tax equity financings have specific terms that dictate distributions of cash and the allocation of tax attributes among the LLC members, who are divided into two categories: the sponsor and third-party investors. ALLETE subsidiaries are the sponsors in these tax equity financings. The distributions of cash and allocation of tax attributes in these financings generally differ from the underlying ownership percentage interests in the related LLC, with a disproportionate share of tax attributes (including accelerated depreciation and production tax credits) allocated to third-party investors in order to achieve targeted after-tax rates of return, or target yield, from project operations, and a disproportionate share of cash distributions made to the sponsor.

The target yield and other terms vary by tax equity financing. Once the target yield has been achieved or defined time period is met, a “flip point” is recognized. In addition, tax equity financings typically provide that cash distributions can be temporarily increased to the third-party investors in order to meet cumulative distribution thresholds. After the flip point, tax attributes and cash distributions are both typically disproportionately allocated to the sponsor.

Tax equity financings include affirmative and negative covenants that are similar to what a project lender would require in a project financing, such as financial reporting, insurance, maintenance and prudent operator standards. Most covenants are no longer applicable once the flip point occurs and any other obligations of the third-party investor have been eliminated.

The third-party investors’ portions of equity ownership in tax equity LLCs are recorded as non-controlling interest in subsidiaries on the Consolidated Balance Sheet and earnings allocated to third-party investors are recorded as net loss attributable to non-controlling interest on the Consolidated Statement of Income.

Non-Controlling Interest in Subsidiaries and Redeemable Non-Controlling Interest. Non-controlling interest in subsidiaries and redeemable non-controlling interest represent the portion of equity ownership, net income (loss), and comprehensive income (loss) in subsidiaries that is not attributable to equity holders of ALLETE. Non-controlling Interest in Subsidiaries as of and for the years ended December 31, 2023 and 2022, are related to the tax equity financings for ALLETE Clean Energy’s 106 MW Glen Ullin, 80 MW South Peak, 303 MW Diamond Spring and 303 MW Caddo wind energy facilities as well as ALLETE’s equity investment in the 250 MW Nobles 2 wind energy facility. Redeemable Non-Controlling Interest as of and for the year ended December 31, 2023, is related to a tax equity financing entered into in the fourth quarter of 2023 for certain New Energy solar energy facilities totaling 14 MW. This tax equity financing is classified as redeemable non-controlling interest as the redemption price and date are fixed and determinable.

For those wind and solar projects with tax equity financings where the economic benefits are not allocated based on the underlying ownership percentage interests, we have determined that the appropriate methodology for calculating the non-controlling interest in subsidiaries balance is the hypothetical liquidation at book value (HLBV) method. The HLBV method is a balance sheet approach which reflects the substantive economic arrangements in the tax equity financing structures.

Under the HLBV method, amounts reported as non-controlling interest in subsidiaries on the Consolidated Balance Sheet represent the amounts the third-party investors would hypothetically receive at each balance sheet reporting date under the liquidation provisions of the LLC agreements, assuming the net assets of the wind and solar projects were liquidated at amounts determined in accordance with GAAP and distributed to the third-party investor and sponsor. The resulting non-controlling interest in subsidiaries balance in these projects is reported as a component of equity on the Consolidated Balance Sheet as either Non-Controlling Interest in Subsidiaries or Redeemable Non-Controlling Interest.

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

The results of operations for these projects attributable to non-controlling interest under the HLBV method is determined as the difference in non-controlling interest in subsidiaries and redeemable non-controlling interest on the Consolidated Balance Sheet at the start and end of each reporting period, after taking into account any capital transactions between the projects and the third-party investors.

Factors used in the HLBV calculation include GAAP income, taxable income (loss), tax attributes such as accelerated depreciation, investment tax credits and production tax credits, capital contributions, cash distributions, and the target yield specified in the corresponding LLC agreement. Changes in these factors could have a significant impact on the amounts that third-party investors and sponsors would receive upon a hypothetical liquidation. The use of the HLBV method to allocate income to the non-controlling interest in subsidiaries may create variability in our results of operations as the application of the HLBV method can drive variability in net income or loss attributable to non-controlling interest in subsidiaries from period to period.

Immaterial Out-of-Period Adjustment. In the third quarter of 2023, we recognized a $5.7 million increase in Net Loss Attributable to Non-Controlling Interest on the Consolidated Statement of Income for the correction of an error related to the calculation of non-controlling interest in subsidiaries under the hypothetical liquidation at book value method, of which $3.6 million related to 2022. We have evaluated the effect of this out-of-period adjustment for the current reporting period, as well as on the previous interim and annual periods in which they should have been recognized and concluded that this adjustment is not material to any of the periods affected.


Other Income (Expense) - Other
Year Ended December 31	2023	2022	2021
Millions
Pension and Other Postretirement Benefit Plan Non-Service Credit (a)	$8.9	$9.8	$6.1
Interest and Investment Income (b)	10.3	—	2.3
AFUDC - Equity	3.6	2.7	2.6
Gain on Land Sales	0.2	—	0.1
PSA Liability (c)	—	10.2	—
Gain on Arbitration Award (d)	58.4	—	—
Other	3.6	(0.3)	(2.4)
Total Other Income (Expense) - Other	$85.0	$22.4	$8.7

(a)These are components of net periodic pension and other postretirement benefit cost other than service cost. (See Note 12. Pension and Other Postretirement Benefit Plans.)

(d)This reflects a gain recognized for the favorable outcome of an arbitration ruling involving a subsidiary of ALLETE Clean Energy. (See Note 9. Commitments, Guarantees and Contingencies.)

Income Taxes. ALLETE and its subsidiaries file a consolidated federal income tax return as well as combined and separate state income tax returns. We account for income taxes using the liability method in accordance with GAAP for income taxes. Under the liability method, deferred income tax assets and liabilities are established for all temporary differences in the book and tax basis of assets and liabilities, based upon enacted tax laws and rates applicable to the periods in which the taxes become payable.

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)

Due to the effects of regulation on Minnesota Power and SWL&P, certain adjustments made to deferred income taxes are, in turn, recorded as regulatory assets or liabilities. Tax credits are recorded when earned unless there is a requirement to defer the benefit and amortize it over the book depreciable lives of the related property. The requirement to defer and amortize tax credits only applies to federal credits related to public utility property. In accordance with GAAP for uncertainty in income taxes, we are required to recognize in our financial statements the largest tax benefit of a tax position that is “more‑likely‑than‑not” to be sustained on audit, based solely on the technical merits of the position as of the reporting date. The term “more‑likely‑than‑not” means more than 50 percent likely. (See Note 11. Income Tax Expense.)

Excise Taxes. We collect excise taxes from our customers levied by governmental entities. These taxes are stated separately on the billing to the customer and recorded as a liability to be remitted to the governmental entity. We account for the collection and payment of these taxes on a net basis.

Operations and Significant Accounting Policies - Other Non-Current Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Business Segments [Line Items]
Asset Retirement Obligation	$ 202.9	$ 200.4
PSAs	20.9	26.9
Other	40.5	41.7
Total Other Non-Current Liabilities	264.3	269.0
BNI Energy
Business Segments [Line Items]
Other receivables	$ 37.2	$ 32.4

Acquisitions (Tables)

12 Months Ended

Dec. 31, 2023

Business Combination and Asset Acquisition [Abstract]

Schedule of Recognized Identified Assets Acquired and Liabilities Assumed


Millions
Assets Acquired
Cash and Cash Equivalents												$3.9
Accounts Receivable												1.4
Inventory (a)												25.3
Other Current Assets												12.8
Property, Plant and Equipment - Net												16.4
Goodwill (b)												154.9
Other Non-Current Assets												2.1
Total Assets Acquired												$216.8
Liabilities Assumed
Current Liabilities												$23.6
Long-Term Debt Due Within One Year												28.3
Long-Term Debt												5.9
Other Non-Current Liabilities												0.2
Total Liabilities Assumed												$58.0
Net Identifiable Assets Acquired												$158.8

(a)Includes $11.6 million of purchase price accounting for certain projects under development at the time of acquisition.

(b)For tax purpose, the purchase price allocation resulted in $154.9 million of deductible goodwill.

Regulatory Matters - Narrative (Details) $ in Millions							12 Months Ended			36 Months Ended
Regulatory Matters - Narrative (Details) $ in Millions	Dec. 19, 2023 USD ($)	Nov. 01, 2023 USD ($)	Feb. 28, 2023 USD ($)	Feb. 27, 2023	Dec. 20, 2022 USD ($)	Nov. 01, 2021 USD ($)	Dec. 31, 2023 USD ($) customer contract MW	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2022 USD ($)	Dec. 15, 2023 MW	Oct. 02, 2023 MW	Sep. 30, 2023 USD ($)	Feb. 01, 2021 MW
Regulatory Matters [Line Items]
Regulatory Assets							$ 425.4	$ 441.0		$ 441.0
Regulatory Liabilities							$ 574.0	526.1		526.1
Minnesota Power \| Solar Generation
Regulatory Matters [Line Items]
Anticipated generating capacity to be purchased (MW) \| MW							20					300
Minnesota Power \| Wind Generation
Regulatory Matters [Line Items]
Anticipated generating capacity to be purchased (MW) \| MW											400
Other \| Solar Generation
Regulatory Matters [Line Items]
Estimated investment amount							$ 40.0
MPUC
Regulatory Matters [Line Items]
Minnesota solar energy standard - overall mandate percentage							1.50%
MPUC \| Minimum
Regulatory Matters [Line Items]
Cip spending minimum - percentage							1.50%
Minnesota solar energy standard - overall mandate percentage							1.50%
Minnesota solar energy standard - small scale solar mandate percentage							10.00%
MPUC \| Minnesota Power \| Solar Generation
Regulatory Matters [Line Items]
Generating capacity (MW) \| MW							40
FERC
Regulatory Matters [Line Items]
FERC authorized return on common equity							10.02%
FERC authorized return on equity including incentive adder							10.52%
ECO Triennial Filing \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Conservation improvement program goal, next fiscal year							$ 12.5
Energy conservation and optimization plan goal, second fiscal year							12.7
Energy conservation and optimization plan goal, third fiscal year							12.8
2021 Integrated Resource Plan \| MPUC \| Maximum \| Renewable Generation
Regulatory Matters [Line Items]
Generating capacity (MW) \| MW														700
CIP Consolidated Filing Member \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Revenue from cost recovery riders							2.2
CIP Consolidated Filing \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Revenue from cost recovery riders								1.9	$ 2.4
Electric Rates \| Fuel Adjustment Clause 2022 \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Regulatory Assets								$ 13.0		$ 13.0
Electric Rates \| Fuel Adjustment Clause 2023 \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Regulatory Liabilities							15.5
Electric Rates \| Fuel Adjustment Clause \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Regulatory Assets									56.0
Retail Customers \| 2018 Wisconsin General Rate Case \| PSCW \| SWL&P
Regulatory Matters [Line Items]
Authorized return on equity										10.40%
Return on common equity										55.00%
Retail Customers \| 2022 Wisconsin General Rate Review \| PSCW \| SWL&P
Regulatory Matters [Line Items]
Requested average rate increase								3.60%
Requested return on equity								10.40%
Requested equity ratio								55.00%
Annual additional revenue generated from requested final rate increase								$ 4.3
Additional revenue from base rates					$ 3.3
Retail Customers \| 2022 Wisconsin General Rate Case \| PSCW \| SWL&P
Regulatory Matters [Line Items]
Authorized return on equity					10.00%
Return on common equity					55.00%
Retail Customers \| Electric Rates \| Current Cost Recovery Rider \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Revenue from cost recovery riders							$ 57.0	38.8	$ 38.9
Retail Customers \| Electric Rates \| 2016 Minnesota General Rate Review \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Authorized return on equity				9.25%
Return on common equity				53.81%
Retail Customers \| Electric Rates \| 2022 Minnesota General Rate Review \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Authorized return on equity			9.65%
Return on common equity			52.50%
Requested average rate increase						18.00%
Requested return on equity						10.25%
Requested equity ratio						53.81%
Annual additional revenue generated from requested final rate increase						$ 108.0
Additional revenue from base rates			$ 60.0
Public utility - additional rider revenue			$ 10.0
Customer refund								$ 18.0		$ 18.0			$ 39.0
Retail Customers \| Electric Rates \| 2024 Minnesota General Rate Case \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Requested average rate increase		12.00%
Requested return on equity		10.30%
Requested equity ratio		53.00%
Annual additional revenue generated from requested final rate increase	$ 64.0	$ 89.0
Municipal Customers \| Electric Rates \| FERC-Approved Wholesale Rates \| FERC \| Minnesota Power
Regulatory Matters [Line Items]
Number of customers \| customer							14
Notice required to terminate							3 years
Municipal Customers \| Electric Rates \| FERC-Approved Wholesale Rates \| FERC \| Minnesota Power \| Wholesale Electric Contract (Cost-Based Formula Methodology for Entire Term)
Regulatory Matters [Line Items]
Number of customers \| contract							2
Municipal Customers \| Electric Rates \| FERC-Approved Wholesale Rates \| FERC \| Minnesota Power \| Wholesale Electric Contracts (Through 2029)
Regulatory Matters [Line Items]
Number of customers \| customer							13

Pension and Other Postretirement Benefit Plans - Obligation and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Change in Plan Assets
Non-Current Liabilities	$ (160.8)	$ (179.7)
Pension
Defined Benefit Plan Disclosure [Line Items]
Accumulated Benefit Obligation	729.5	724.5
Change in Benefit Obligation [Roll Forward]
Obligation, Beginning of Year	739.7	911.7
Service Cost	6.5	9.3	$ 11.0
Interest Cost	40.5	27.2	24.6
Plan Amendments	0.0	0.8
Actuarial (Gain) Loss	13.9	(160.6)
Benefits Paid	(60.9)	(58.9)
Participant Contributions	6.6	10.2
Obligation, End of Year	746.3	739.7	911.7
Change in Plan Assets
Fair Value, Beginning of Year	568.6	745.7
Actual Return on Plan Assets	55.1	(130.5)
Employer contribution	26.2	12.3
Benefits Paid	(60.9)	(58.9)
Fair Value, End of Year	589.0	568.6	745.7
Funded Status, End of Year	(157.3)	(171.1)
Current Liabilities	(2.1)	(2.1)
Non-Current Liabilities	(155.2)	(169.0)
Postretirement Health and Life Obligation and Funded Status
Change in Benefit Obligation [Roll Forward]
Obligation, Beginning of Year	110.4	148.2
Service Cost	2.0	3.0	3.6
Interest Cost	5.6	4.4	4.4
Plan Amendments	(29.1)	0.0
Actuarial (Gain) Loss	(9.3)	(38.7)
Benefits Paid	(8.1)	(9.2)
Participant Contributions	2.4	2.7
Obligation, End of Year	73.9	110.4	148.2
Change in Plan Assets
Fair Value, Beginning of Year	162.6	201.8
Actual Return on Plan Assets	20.3	(33.0)
Employer Contribution (Withdrawal)	(3.4)
Employer contribution		0.3
Benefits Paid	(8.1)	(9.2)
Participant Contributions	2.4	2.7
Fair Value, End of Year	173.8	162.6	$ 201.8
Funded Status, End of Year	99.9	52.2
Non-Current Assets	106.3	58.8
Current Liabilities	(0.2)	(0.2)
Non-Current Liabilities	$ (6.2)	$ (6.4)

Common Stock and Earnings Per Share

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Common Stock and Earnings Per Share

COMMON STOCK AND EARNINGS PER SHARE


Summary of Common Stock	Shares	Equity
	Thousands	Millions
Balance as of December 31, 2020	52,085	$1,460.9
Employee Stock Purchase Plan	17	0.8
Invest Direct	263	17.5
Share-Based Compensation	73	6.5

Equity Issuance Program	782	51.0




Balance as of December 31, 2021	53,220	1,536.7
Employee Stock Purchase Plan	11	0.9
Invest Direct	244	14.9
Share-Based Compensation	82	5.3

Equity Issuance	3,680	223.7




Balance as of December 31, 2022	57,237	1,781.5
Employee Stock Purchase Plan	16	0.8
Invest Direct	232	13.3
Share-Based Compensation	76	8.1





Balance as of December 31, 2023	57,561	$1,803.7

Equity Issuance Program. We entered into a distribution agreement with Lampert Capital Markets, in 2008, as amended most recently in 2020, with respect to the issuance and sale of up to an aggregate of 13.6 million shares of our common stock, without par value, of which 2.1 million shares remain available for issuance as of December 31, 2023. For the year ended December 31, 2023, no shares of common stock were issued under this agreement (none in 2022; 0.8 million for net proceeds of $51.0 million in 2021). On April 5, 2022, ALLETE issued and sold approximately 3.7 million shares of ALLETE common stock. Net proceeds of approximately $224 million were received from the sale of shares. Proceeds were used primarily to fund the acquisition of New Energy and capital investments at ALLETE Clean Energy.

Earnings Per Share. We compute basic earnings per share using the weighted average number of shares of common stock outstanding during each period. The difference between basic and diluted earnings per share, if any, arises from non-vested restricted stock units and performance share awards granted under our Executive Long-Term Incentive Compensation Plan.


Reconciliation of Basic and Diluted
Earnings Per Share		Dilutive
Year Ended December 31	Basic	Securities	Diluted
Millions Except Per Share Amounts
2023
Net Income Attributable to ALLETE	$247.1		$247.1
Average Common Shares	57.3	0.1	57.4
Earnings Per Share	$4.31		$4.30

2022
Net Income Attributable to ALLETE	$189.3		$189.3
Average Common Shares	55.9	0.1	56.0
Earnings Per Share	$3.38		$3.38

2021
Net Income Attributable to ALLETE	$169.2		$169.2
Average Common Shares	52.4	0.1	52.5
Earnings Per Share	$3.23		$3.23

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
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-URI https://asc.fasb.org//1943274/2147481004/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-16

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

+ Details

Regulatory Matters (Tables)

12 Months Ended

Dec. 31, 2023

Regulated Operations [Abstract]

Schedule of Regulatory Assets and Liabilities


Regulatory Assets and Liabilities
As of December 31	2023	2022
Millions
Current Regulatory Assets (a)
Fuel Adjustment Clause (b)	$8.7	$25.6
Other	0.6	—
Total Current Regulatory Assets	$9.3	$25.6
Non-Current Regulatory Assets

Defined Benefit Pension and Other Postretirement Benefit Plans (c)	$218.6	$225.9

Income Taxes (d)	88.1	97.6
Asset Retirement Obligations (e)	37.7	35.6
Cost Recovery Riders (f)	33.8	41.2
Taconite Harbor (g)	20.9	—
Manufactured Gas Plant (h)	13.2	15.1
Fuel Adjustment Clause (b)	5.0	14.5
PPACA Income Tax Deferral	3.9	4.1


Other	4.2	7.0
Total Non-Current Regulatory Assets	$425.4	$441.0


Current Regulatory Liabilities (i)
Provision for Interim Rate Refund	—	$18.4


Transmission Formula Rates Refund	$1.5	4.9
Other	2.4	0.1
Total Current Regulatory Liabilities	$3.9	$23.4
Non-Current Regulatory Liabilities

Income Taxes (d)	$310.0	$332.5
Wholesale and Retail Contra AFUDC (j)	78.0	80.7
Plant Removal Obligations (k)	67.0	60.0

Defined Benefit Pension and Other Postretirement Benefit Plans (c)	48.6	17.6
Non-Jurisdictional Land Sales (l)	30.2	7.5
Fuel Adjustment Clause (b)	15.5	—
Investment Tax Credits (m)	13.6	16.9
Boswell Units 1 and 2 Net Plant and Equipment (n)	6.7	6.7


Other	4.4	4.2
Total Non-Current Regulatory Liabilities	$574.0	$526.1

(a)Current regulatory assets are presented within Prepayments and Other on the Consolidated Balance Sheet.

(e)Asset retirement obligations will accrete and be amortized over the lives of the related property with asset retirement obligations.

(i)Current regulatory liabilities are presented within Other Current Liabilities on the Consolidated Balance Sheet.

(k)Non-legal plant removal obligations included in retail customer rates that have not yet been incurred.

Pension and Other Postretirement Benefit Plans - Recurring Fair Value Measures (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	$ 589.0	$ 568.6	$ 745.7
Pension \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	155.0	134.3
Pension \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	415.1	411.9
Pension \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	18.9	22.4
Pension \| U.S. Large-cap
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	83.7	61.2
Pension \| U.S. Large-cap \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| U.S. Large-cap \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	83.7	61.2
Pension \| U.S. Large-cap \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| U.S. Mid-cap Growth
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	69.9	40.0
Pension \| U.S. Mid-cap Growth \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| U.S. Mid-cap Growth \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	69.9	40.0
Pension \| U.S. Mid-cap Growth \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| U.S. Small-cap
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	46.5	35.4
Pension \| U.S. Small-cap \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| U.S. Small-cap \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	46.5	35.4
Pension \| U.S. Small-cap \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| International
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	134.6	127.0
Pension \| International \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	134.6	127.0
Pension \| International \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| International \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| Fixed Income Securities
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	215.0	275.3
Pension \| Fixed Income Securities \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| Fixed Income Securities \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	215.0	275.3
Pension \| Fixed Income Securities \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| Cash and Cash Equivalents
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	20.4	7.3
Pension \| Cash and Cash Equivalents \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	20.4	7.3
Pension \| Cash and Cash Equivalents \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| Cash and Cash Equivalents \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| Real Estate
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	18.9	22.4
Pension \| Real Estate \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| Real Estate \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension \| Real Estate \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	18.9	22.4	21.6
Postretirement Health and Life
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	173.8	162.6	201.8
Postretirement Health and Life \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	173.8	162.6
Postretirement Health and Life \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life \| U.S. Large-cap
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	30.0	26.7
Postretirement Health and Life \| U.S. Large-cap \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	30.0	26.7
Postretirement Health and Life \| U.S. Large-cap \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life \| U.S. Large-cap \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life \| U.S. Mid-cap Growth
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	28.7	25.5
Postretirement Health and Life \| U.S. Mid-cap Growth \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	28.7	25.5
Postretirement Health and Life \| U.S. Mid-cap Growth \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life \| U.S. Mid-cap Growth \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life \| U.S. Small-cap
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	14.9	12.7
Postretirement Health and Life \| U.S. Small-cap \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	14.9	12.7
Postretirement Health and Life \| U.S. Small-cap \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life \| U.S. Small-cap \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life \| International
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	41.9	41.5
Postretirement Health and Life \| International \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	41.9	41.5
Postretirement Health and Life \| International \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life \| International \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life \| Cash and Cash Equivalents
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	3.2	0.7
Postretirement Health and Life \| Cash and Cash Equivalents \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	3.2	0.7
Postretirement Health and Life \| Cash and Cash Equivalents \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life \| Cash and Cash Equivalents \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life \| Private Equity \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets		0.0	$ 2.0
Postretirement Health and Life \| Mutual Funds
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	55.1	55.5
Postretirement Health and Life \| Mutual Funds \| Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	55.1	55.5
Postretirement Health and Life \| Mutual Funds \| Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life \| Mutual Funds \| Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	$ 0.0	$ 0.0