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Authorized return on equity, including incentive adder Equity Method Investment, Approved Return on Common Equity, Including Incentive Adder The approved percentage return on common equity, including an incentive adder for participation in a regional transmission organization dedicated to the utility plant in the investee accounted for under the equity method of accounting. 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Utility Fuel, Purchased Power and Gas - Utility Investment Tax Credit Amortization Deferred Other Tax Expense (Benefit) Property-Related Deferred Tax Liabilities, Property, Plant and Equipment Name Outstanding Recovery, Individual Name Authorized return on equity Equity Method Investment, Approved Return on Common Equity The approved percentage return on common equity dedicated to the utility plant in the investee accounted for under the equity method of accounting. 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Transmission Electric Transmission [Member] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Notice required to terminate Length of Notice Required to Terminate (Years) The length of notice required to terminate a contract (in years). 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May 2025 Basin Electric Cooperative PSA June 2023 - May 2025 [Member] Basin Electric Cooperative PSA June 2023 - May 2025 [Member] PEO PEO [Member] Name Trading Arrangement, Individual Name Funded Status, End of Year Defined Benefit Plan, Funded (Unfunded) Status of Plan Property, Plant and Equipment, Type [Axis] Long-Lived Tangible Asset [Axis] Total Unrecognized Postretirement Health and Life Credit Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax 2.79% Series Due 2031 2.79% Series Due 2031 [Member] 2.79% Series Due 2031 Entity Public Float Entity Public Float Other Postretirement Benefit Plans Other Postretirement Benefit Plans Other Postretirement Benefit Plans Excise Taxes Excise Tax Policy [Policy Text Block] Policy regarding the collection and recording of excise taxes. Regulatory Proceeding [Domain] Public Utilities, Regulatory Proceeding [Domain] Equity Earnings Equity in ATC Earnings Income (Loss) from Equity Method Investments Commitments, Guarantees and Contingencies Commitments Contingencies and Guarantees [Text Block] Wind Generation Wind Generation [Member] Wind Generation Obligation, Beginning of Year Obligation, End of Year Defined Benefit Plan, Benefit Obligation Output being purchased (MW) Long-Term Contract for Purchase of Electric Power, Share of Plant Output Purchased (MW) Long-Term Contract for Purchase of Electric Power, Share of Plant Output Purchased Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Other Income (Expense) Other Nonoperating Income (Expense) [Abstract] Fuel Adjustment Clause Increase (Decrease) in Regulatory Clause Revenue Common stock reserved (in shares) Common Stock, Capital Shares Reserved for Future Issuance SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Jointly-Owned Facilities and Assets [Line Items] Jointly Owned Utility Plant Interests [Line Items] Output being sold electric - energy and capacity (MW) Long-term Contract for Sale of Electric Energy and Capacity (MW) Long-term Contract for Sale of Electric Energy and Capacity (MW) Purchase option Purchase Option, Asset Purchase option to acquire an asset. Natural Gas Natural Gas [Member] Natural Gas Customer [Member] Cost of purchased power Utilities Operating Expense, Purchased Power under Long-Term Contracts Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Local Phone Number Local Phone Number Deferred Income Tax Asset Valuation Allowance Deferred Tax Assets, Valuation Allowance Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] ALLETE Bonds 5.72% Due April 2039 ALLETE Bonds 5.72% Due April 2039 [Member] ALLETE Bonds 5.72% Due April 2039 Equity Investments [Table] Equity Method Investment [Table] Pension and Other Postretirement Benefit Plan Non-Service Credit Pension and Other Postretirement Benefit Plans Non-Service Credit [Member] Pension and Other Postretirement Benefit Plans Non-Service Credit [Member] Weighted Average Remaining Lease Term (Years): Weighted Average Remaining Lease Term [Abstract] Weighted Average Remaining Lease Term Changes in Operating Assets and Liabilities Increase (Decrease) in Operating Capital [Abstract] PEO Total Compensation Amount PEO Total Compensation Amount Requested return on equity Public Utilities, Requested Return on Equity, Percentage Senior Unsecured Notes 2.65% Due 2025 Unsecured Senior Notes 2.65% Due 2025 [Member] Unsecured Senior Notes 2.65% Due 2025 Property, Plant and Equipment, Type [Domain] Long-Lived Tangible Asset [Domain] Accrued Interest Interest Payable, Current Plan Asset Categories [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Axis] Defined Benefit Plan, Plan Assets, Category [Axis] Debt Disclosure [Abstract] Debt Disclosure [Abstract] Common Stock Common Stock [Member] Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Other Current Assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Deferred Compensation Deferred Compensation Liability, Classified, Noncurrent Gross Unrecognized Income Tax Benefits [Abstract] Income Tax Uncertainties [Abstract] Segment Reporting [Abstract] Segment Reporting [Abstract] Entity Central Index Key Entity Central Index Key 3.30% Series Due 2028 ALLETE Bonds 3.30% Due October2028 [Member] ALLETE Bonds 3.30% Due October2028 [Member] Scenario [Axis] Scenario [Axis] Other Segment Items Segment Reporting, Other Segment Item, Amount Inventories – Net Schedule of Inventory, Current [Table Text Block] Equity Method Investments and Joint Ventures [Abstract] Equity Method Investments and Joint Ventures [Abstract] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Common Stock and Earnings Per Share Equity [Text Block] Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Business Segments Segment Reporting Disclosure [Text Block] Long-Term Debt Due Within One Year Less: Due Within One Year Long-Term Debt, Current Maturities 2025 Unrecorded Unconditional Purchase Obligation, to be Paid, Year One Minimum Annual Payments for Certain Long-Term Commitments [Domain] Unconditional Purchase Obligation, Category of Goods or Services Acquired [Domain] Title Trading Arrangement, Individual Title Prepayments And Other Prepayments And Other [Member] Prepayments And Other Other Corporate & Other - Other [Member] Revenue Recognized by Corporate & Other From Other Sources Immaterial for Disaggregation Share-Based Compensation (in shares) Share-Based Compensation - Shares Share-Based Compensation - Shares Employee Stock Ownership Plan Employee Stock Ownership Plan (ESOP), Policy [Policy Text Block] Balance at January 1 Balance as of December 31 Unrecognized Tax Benefits Net Loss Attributable to Non-Controlling Interest Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Federal Internal Revenue Service (IRS) [Member] Variable Interest Entities Consolidation, Variable Interest Entity, Policy [Policy Text Block] Proceeds from Non-Controlling Interest in Subsidiaries Temporary Equity, Interest in Subsidiary Earnings City Area Code City Area Code Current Liabilities Liabilities, Current [Abstract] Auditor Location Auditor Location Net book value Public Utilities, Property, Plant and Equipment, Net Large Power Customers Large Power Customer [Member] Large Power Customer [Member] Other Income (Expense) - Other [Table] Other Income (Expense) - Other [Table] Other Income (Expense) - Other [Table] Revenue Recognition Revenue [Policy Text Block] Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block] 2018 Wisconsin General Rate Case 2018 Wisconsin General Rate Case [Member] 2018 retail rate increase request filed with the PSCW [Member] Jointly-Owned Facilities and Assets Schedule of Jointly Owned Utility Plants [Table Text Block] Employer contributions to defined benefit pension plans - cash Defined Benefit Plan, Plan Assets, Cash Contributions by Employer Defined Benefit Plan, Plan Assets, Cash Contributions by Employer Deferred Tax Assets SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member] Pension and Other Postretirement Benefit Plans Pension and Other Postretirement Plans, Policy [Policy Text Block] Long-Term Debt Long-term debt outstanding Net Long-Term Debt Long-Term Debt, Excluding Current Maturities Valuation and Qualifying Accounts and Reserves [Table] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] Business Segments [Table] Schedule of Segment Reporting Information, by Segment [Table] Letters of Credit Financial Standby Letter of Credit [Member] Weighted- Average Grant Date Fair Value Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Average Shares of Common Stock Earnings Per Share [Abstract] Equity [Abstract] Equity [Abstract] Retained Earnings Retained Earnings (Accumulated Deficit) Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Class of Stock [Domain] Class of Stock [Domain] Silver Bay Power Silver Bay Power [Member] Silver Bay Power [Member] Long-term Contracts for Sale of Electric Power [Axis] Long-term Contracts for Sale of Electric Power [Axis] Long-term Contracts for Sale of Electric Power [Axis] Asset Retirement Obligations Asset Retirement Obligation Costs [Member] Inventories Increase (Decrease) in Inventories Capitalized Asset Retirement Costs Increase (Decrease) in Asset Retirement Obligations Long-term debt maturing in 2026 Long-Term Debt, Maturity, Year Two Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Equity Awards Adjustments Equity Awards Adjustments [Member] Total Lease Obligations Operating Lease, Liability Purchases, Sales, and Settlements – Net Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Purchase, Sale, and Settlement WPPI Energy ownership Jointly-Owned Electric Facility Percentage Not Owned Jointly-Owned Electric Facility Percentage Not Owned Underlying Securities Award Underlying Securities Amount Performance Shares Performance Shares [Member] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Total Current Regulatory Assets Regulatory Asset, Current Caddo Caddo [Member] Caddo Weighted Average Assumptions Used to Determine Net Periodic Benefit Costs Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract] 2029 Finance Lease, Liability, to be Paid, Year Five Common Stock Dividends Dividends, Common Stock, Cash Amendment Flag Amendment Flag Participant Contributions Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant Revolving Credit Facility Variable Rate Due 2027 Revolving Credit Facility Variable Rate Due 2025 [Member] Revolving Credit Facility Variable Rate Due 2025 Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Redeemable Non-Controlling Interest Increase (Decrease) in Temporary Equity [Roll Forward] Restrictions on Cash and Cash Equivalents Restrictions on Cash and Cash Equivalents [Table Text Block] Provision for Interim Rate Refund Provision for Interim Rate Refund [Member] Provision for Interim Rate Refund Industrial Development Variable Rate Demand Refunding Revenue Bonds Series 2006, Due 2025 Industrial Development Variable Rate Demand Refunding Revenue Bonds Series 2006 Due 2025 [Member] Industrial Development Variable Rate Demand Refunding Revenue Bonds Series 2006 Due 2025 [Member] Finance Lease Amortization Expense Finance Lease, Right-of-Use Asset, Amortization Subsequent Events [Abstract] Actual Return on Plan Assets Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) Unamortized Debt Issuance Costs Debt Issuance Costs, Net Short-Term and Long-Term Debt Debt Disclosure [Text Block] Fair Value Hierarchy and NAV [Domain] Total [Domain] Fair Value Hierarchy and NAV [Domain] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Proceeds from issuance of long-term debt Debt Instrument, Face Amount Annual Debt Service Period [Domain] Annual Debt Service Period [Domain] [Domain] for Annual Debt Service Period [Axis] Performance period Share-Based Compensation Arrangement by Share-Based Payment Award, Performance Period Share-Based Compensation Arrangement by Share-Based Payment Award, Performance Period Entity Address, Postal Zip Code Entity Address, Postal Zip Code ESOP compensation expense Employee Stock Ownership Plan (ESOP), Compensation Expense Square Butte Coal-fired Unit Square Butte Coal-fired Unit [Member] Square Butte Coal-fired Unit located near Center, North Dakota Alternative Programs Alternative Programs [Member] Alternative Programs Sales Channel [Member] Cash and Cash Equivalents Cash and Cash Equivalents, at Carrying Value Customer Class [Axis] Customer Class [Axis] Customer Class [Axis] description of customer types or classes Amounts Recognized in Consolidated Balance Sheet Schedule of Amounts Recognized in Balance Sheet [Table Text Block] Basin Basin [Member] Basin [Member] Other Investing Activities Payments for (Proceeds from) Other Investing Activities Retail Electric Service Retail Electric Service [Member] Retail Electric Service [Member] Other Current Liabilities Increase (Decrease) in Other Current Liabilities Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Quarterly Financial Data (Unaudited) Quarterly Financial Information [Table Text Block] Auditor Name Auditor Name Forfeited (in usd per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Silver Bay Power Self-Generation Silver Bay Power Coal, Liquid and Gaseous Fuels-fired Units [Member] Silver Bay Power Coal, Liquid and Gaseous Fuels-fired Units [Member] Current Income Tax Expense Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Regulatory Matters [Table] Public Utilities General Disclosures [Table] 5.72% Series Due 2039 5.72% Series Due 2039 [Member] 5.72% Series Due 2039 Estimated Useful Lives Property, Plant and Equipment, Useful Life Employee Stock Purchase Plan (ESPP) Employee Stock [Member] Equity Method Investment, Nonconsolidated Investee [Axis] Equity Method Investment, Nonconsolidated Investee [Axis] Accounts Payable Increase (Decrease) in Accounts Payable Environmental Remediation Contingency [Domain] Environmental Remediation Contingency [Domain] Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Financing Cash Flows From Finance Leases Finance Lease, Principal Payments Other Power Supplier Customers Other Power Supplier Customers [Member] Other Power Supplier Customers Government Grants Government Assistance [Policy Text Block] Regulatory Liabilities Deferred Tax Assets, Regulatory Liabilities Deferred Tax Assets, Regulatory Liabilities Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Summary of Common Stock [Table] Stock, Class of Stock [Table] Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Projected Benefit Obligation Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation Total Assets Total Assets Assets Assets Deferred Accounting Petition Deferred Accounting Petition [Member] Deferred Accounting Petition Cost of Sales – Non-utility Cost of Goods and Services Sold Guarantor Obligations [Table] Guarantor Obligation [Table] Valuation allowance Operating loss carryforwards, valuation allowance Operating Loss Carryforwards, Valuation Allowance Oliver Wind II PPA Oliver Wind II PPA [Member] Long-term contract with an affiliate of NextEra Energy, Inc. for the purchase of electric power. Additions to Property, Plant and Equipment Payments to Acquire Property, Plant, and Equipment Other Non-Current Liabilities Total Other Non-Current Liabilities Other Liabilities, Noncurrent Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Commitments, Guarantees and Contingencies (Note 9) Commitments and Contingencies Accounting for Stock-Based Compensation Share-Based Payment Arrangement [Policy Text Block] Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Fair value adjustments Business Combinations, Fair Value Adjustments Business Combinations, Fair Value Adjustments Termination Date Trading Arrangement Termination Date Generating capacity counterparty owned (MW) Generating Capacity Counterparty Owned (MW) Generating Capacity Counterparty Owned (MW) SWL&P First Mortgage Bonds 4.15% Series Due 2028 SWL&P First Mortgage Bonds 4.15% Series Due 2028 [Member] SWL&P First Mortgage Bonds 4.15% Series Due 2028 [Member] Recurring Fair Value Measures [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] 2026 Lessee, Operating Lease, Liability, to be Paid, Year Two Long-term debt maturing in 2025 Long-Term Debt, Maturity, Year One Number of remaining covered states Accrual for Environmental Loss Contingencies, Number Of Remaining Covered States Accrual for Environmental Loss Contingencies, Number Of Remaining Covered States Power Purchase Agreement - Capacity [Axis] Long-term Contract for Purchase of Electric Capacity [Axis] Long-term Contract for Purchase of Electric Capacity [Axis] Standby letters of credit and surety bonds outstanding Letters Of Credit And Guarantor Obligations, Collateral Held Directly Or By Third Parties, Amount Letters Of Credit And Guarantor Obligations, Collateral Held Directly Or By Third Parties, Amount Nobles 2 PPA Tenaska PPA [Member] Tenaska PPA [Member] South Shore Energy South Shore Energy [Member] South Shore Energy Schedule of Recognized Identified Assets Acquired and Liabilities Assumed Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Debt Instrument [Axis] Debt Instrument [Axis] Deferred Gain - Land Sales Deferred ​Tax​ Assets​, Deferred Gain Land Sales Deferred ​Tax​ Assets​, Deferred Gain Land Sales Net Income Attributable to ALLETE Net Income Attributable to ALLETE Net Income Attributable to ALLETE Net Income (Loss) Attributable to Parent Trading Arrangement: Trading Arrangement [Axis] Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Years 2030 – 2034 Defined Benefit Plan, Expected Future Benefit Payment, after Year Five for Next Five Years Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Plan Asset Actual and Target Allocations Schedule of Allocation of Plan Assets [Table Text Block] Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] CIP Consolidated Filing CIP Consolidated Filing [Member] CIP Consolidated Filing [Member] Entity File Number Entity File Number Weighted Average Assumptions Used to Determine Benefit Obligation and Net Periodic Benefit Costs Defined Benefit Plan, Assumptions [Table Text Block] AFUDC - Equity AFUDC - Equity [Member] AFUDC - Equity [Member] ALLETE South Wind ALLETE South Wind [Member] ALLETE South Wind Non-Controlling Interest in Subsidiaries Noncontrolling Interest [Member] Income Statement Data [Abstract] Income Statement [Abstract] Entity Address, Address Line Entity Address, Address Line One Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] Federal Current Federal Tax Expense (Benefit) Material changes to unrecognized tax benefits expected during next 12 months Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit Calpine Corporation PPA Calpine Corporation PPA [Member] Calpine Corporation PPA Name Forgone Recovery, Individual Name Operating Leases Operating Lease, Weighted Average Remaining Lease Term Wholesale Electric Service Wholesale Electric Service [Member] Wholesale Electric Service [Member] Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Estimated Future Benefit Payments Schedule of Expected Benefit Payments [Table Text Block] Invest Direct Stock Issued During Period, Value, Dividend Reinvestment Plan Reductions for Tax Positions Related to Prior Years Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions Auditor Information [Abstract] Auditor Information [Abstract] Auditor Information Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount 4.47% Series Due 2049 ALLETE Bonds 4.47% Due March 2049 [Member] ALLETE Bonds 4.47% Due March 2049 [Member] Fair Value of Financial Instruments [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Adjustment to Compensation: Adjustment to Compensation [Axis] Net Loss Attributable to Non-Controlling Interest Net Loss Attributable to Non-Controlling Interest Net loss attributable to non-controlling interest Net Income (Loss) Attributable to Noncontrolling Interest NOL and Tax Credit Carryforwards [Line Items] NOL and Tax Credit Carryforwards [Line Items] NOL and Tax Credit Carryforwards [Line Items] Regulatory Agency [Axis] Regulatory Agency [Axis] Industrial Customers Industrial Customers [Member] Industrial Customers Equity issuance program shares authorized (in shares) Equity Issuance Program Shares Authorized Aggregate number of shares, without par value, authorized to be issued under the distribution agreement with KCCI (equity issuance program/PIE). Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Income (Loss), Net of Tax Renewable Generation Renewable Generation [Member] Renewable Generation Approximate refund for reversal of FERC ROE Order, ALLETE's proportionate share Approximate Refund for Reversal of FERC ROE Order, ALLETE's Proportionate Share Approximate Refund for Reversal of FERC ROE Order, ALLETE's Proportionate Share Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Environmental Matters [Table] Site Contingency [Table] Interest Income Related To Interest Awarded As Part Of An Arbitration Ruling Interest Income Related To Interest Awarded As Part Of An Arbitration Ruling [Member] Interest Income Related To Interest Awarded As Part Of An Arbitration Ruling Related Party [Axis] Related and Nonrelated Parties [Axis] WPPI Energy WPPI Energy [Member] WPPI Energy [Member] Basic (in shares) Average Common Shares (in shares) Weighted Average Number of Shares Outstanding, Basic Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Unrealized gain (loss) on securities, income tax expense (benefit) OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax Total Equity Balance, Beginning of Period Balance, End of Period Members’ Equity Equity, Including Portion Attributable to Noncontrolling Interest Regulatory Agency [Domain] Regulatory Agency [Domain] Property, Plant and Equipment - Net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Plan Asset Target Allocations Defined Benefit Plan, Plan Assets, Target Allocation, Percentage Deferred Income Tax Assets and Liabilities [Abstract] Components of Deferred Tax Assets and Liabilities [Abstract] Ownership percentage of benefited property Community Development District Obligation, Ownership of Property Benefited Ownership percentage of property benefited by a real estate development project funded by municipal capital improvement revenue and special assessment bonds. Name Awards Close in Time to MNPI Disclosures, Individual Name Year Ultimate Trend Rate Effective Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate Contract with Customer, Duration [Axis] Contract with Customer, Duration [Axis] Consolidated Operating Revenue Revenue Benchmark [Member] Long-term Contract for Sale of Capacity [Domain] Long-term Contract for Sale of Capacity [Domain] [Domain] for Long-term Contract for Sale of Capacity [Axis] Approximate refund for reversal of FERC ROE order Approximate Refund for Reversal of FERC ROE Order Approximate Refund for Reversal of FERC ROE Order Jointly-Owned Facilities and Assets [Axis] Jointly Owned Utility Plant [Axis] Current Cost Recovery Rider Current Cost Recovery Rider [Member] Current Cost Recovery Rider [Member] Entity Filer Category Entity Filer Category Other Current Liabilities Other Current Liabilities [Table Text Block] Revenue, remaining performance obligation, amount Revenue, Remaining Performance Obligation, Amount 4.07% Series Due 2048 ALLETE Bonds 4.07% Due April 2048 [Member] ALLETE Bonds 4.07% Due April 2048 [Member] 2016 Minnesota General Rate Review 2016 Minnesota General Rate Review [Member] 2016 Minnesota General Rate Review Liabilities Settled Asset Retirement Obligation, Liabilities Settled Payments for Purchase of Available-for-sale Securities Payments For Purchase Of Available-For-Sale Securities Payments For Purchase Of Available-For-Sale Securities Corporate and Other Corporate and Other / Eliminations Corporate Segment and Other Operating Segment [Member] Regulatory Assets and Liabilities Public Utilities, Policy [Policy Text Block] Customer refund Customer Refund Liability, Current Statistical Measurement [Domain] Statistical Measurement [Domain] Capital Expenditures Segment, Expenditure, Addition to Long-Lived Assets Discount rate - input for goodwill analysis Discount Rate - Input for Goodwill Analysis Discount Rate - Input for Goodwill Analysis Town Center District Capital Improvement Bonds Town Center Community Development District [Member] Community development district obligations for Town Center District. Components of Lease Cost Lease, Cost [Table Text Block] FERC authorized return on equity including incentive adder FERC Authorized Return on Equity, Including Incentive Adder FERC Authorized Return on Equity, Including Incentive Adder Retail Customers Retail Customers [Member] Retail Customers [Member] include residential customers, commercial customers and industrial customers. Transmission Services – Utility Transmission Services - Utility Transmission Services - Utility Component of Other Income (Expense) - Other [Domain] Component of Other Income (Expense) - Other [Domain] [Domain] for Component of Other Income (Expense) - Other [Axis] 3.30% Series Due 2050 ALLETE Bonds 3.30% Due August 2050 [Member] ALLETE Bonds 3.30% Due August 2050 Other Total Other Current Liabilities Other Liabilities, Current Net unrecognized tax benefits Unrecognized Tax Benefits that Would Impact Effective Tax Rate Great River Energy Great River Energy [Member] Great River Energy [Member] Revisions in Estimated Cash Flows Asset Retirement Obligation, Revision of Estimate Business Segments [Line Items] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Basis point incentive adder Basis Point Incentive adder Basis Point Incentive adder All Trading Arrangements All Trading Arrangements [Member] Accumulated Depreciation Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Reconciliation of Basic and Diluted Earnings Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Vesting period Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period Other Other [Member] Regulated Operations Other Revenue Recognized From Other Sources Immaterial For Disaggregation Tax Credit Carryforwards Tax Credit Carryforward, Amount Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Jointly-Owned Facilities and Projects [Domain] Jointly-Owned Utility Plant [Domain] Jointly Owned Utility Plant [Domain] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Selected Quarterly Financial Information [Abstract] Selected Quarterly Financial Information [Abstract] Valuation and Qualifying Accounts and Reserves [Line Items] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] Cash Paid for Income Taxes Income Taxes Paid, Net Generating capacity subject to tax equity financing Generating Capacity Subject to Tax Equity Financing Generating Capacity Subject to Tax Equity Financing 4.90% Series Due 2025 4.90% Series Due 2025 [Member] First Mortgage Bonds, 4.90% Series Due 2025 [Member] Share-Based Compensation Expense Share-Based Payment Arrangement, Cost by Plan [Table Text Block] Expected period for costs of compliance Expected Period for Costs of Compliance Expected Period for Costs of Compliance Equity Investments Equity Investment Beginning Balance Equity Investment Ending Balance Equity Investment Equity Method Investments Pay vs Performance Disclosure [Line Items] Construction Work in Progress Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Fuel Adjustment Clause 2022 Fuel Adjustment Clause 2022 [Member] Fuel Adjustment Clause 2022. Related to the 2022 Fuel Adjustment Clause year. Regulatory Matters Public Utilities Disclosure [Text Block] Other Income (Expense) - Other [Line Items] Other Income (Expense) - Other [Line Items] [Line Items] for Other Income (Expense) - Other [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Contract term Long-term Contract for Purchase of Electric Power, Term of Contract (Years) Term in years of long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. Goodwill and Intangible Assets – Net Intangible Assets, Net (Including Goodwill) Deferred Income Tax Expense (Benefit) Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract] Common Stock [Abstract] Common Stock, Number of Shares, Par Value and Other Disclosure [Abstract] Other Performance Measure, Amount Other Performance Measure, Amount Rate of Compensation Increase Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase Plant in Service Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service Common stock, shares outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Invest Direct (in shares) Stock Issued During Period, Shares, Dividend Reinvestment Plan Documents Incorporated by Reference Documents Incorporated by Reference [Text Block] Operating Lease Cost Operating Lease Rent Expense Operating Lease, Cost Vehicles and Equipment Vehicles and Equipment [Member] Vehicles and Equipment [Member] Shares available for issuance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant Operating Lease Liabilities Operating Lease, Liability, Noncurrent Benefits Paid Defined Benefit Plan, Benefit Obligation, Benefits Paid 4.21% Series Due 2043 ALLETE Bonds 4.21% Due October2043 [Member] ALLETE Bonds 4.21% Due October2043 [Member] Senior Unsecured Notes 6.18% Due 2034 Unsecured Senior Notes 6.18% Due 2034 [Member] Unsecured Senior Notes 6.18% Due 2034 Non-Current Assets Assets, Noncurrent Other Income (Expense) Other Income (Expense) - Other [Member] Other Income (Expense) - Other [Member] Finance Lease Interest Expense Finance Lease, Interest Expense Customer Deposits Contract with Customer, Liability, Current Contract with Customer, Sales Channel [Axis] Contract with Customer, Sales Channel [Axis] Service Cost Defined Benefit Plan, Service Cost Entity Tax Identification Number Entity Tax Identification Number Indicators of impairment Equity Method Investment, Other-than-Temporary Impairment Long-term Contract Long-term Contract [Member] Long-term Contract Revenue Stream [Member] Minnkota Sales Agreement Minnkota Sales Agreement [Member] Minnkota Sales Agreement [Member] Long-term Debt Schedule of Long-Term Debt Instruments [Table Text Block] Asset Retirement Obligation [Roll Forward] Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] Power Purchase Agreements [Axis] Long-Term Contract for Purchase of Electric Power [Axis] Rate Type [Domain] Rate Type [Domain] Rate Type [Domain] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Ultimate Trend Rate Defined Benefit Plan, Ultimate Health Care Cost Trend Rate Nobles 2 Nobles 2 [Member] Nobles 2 [Member] Rate of Compensation Increase Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] PSA Liability PSA Liability [Member] PSA Liability Accrued Taxes Taxes Payable, Current 3.74% Series Due 2029 ALLETE Bonds 3.74% Due September 2029 [Member] ALLETE Bonds 3.74% Due September 2029 [Member] Asset Retirement Obligation Asset Retirement Obligations, Noncurrent Plan Name [Axis] Plan Name [Axis] Requested average rate increase Public Utilities, Requested Rate Increase (Decrease), Percentage Equity Components [Axis] Equity Components [Axis] Equity Components [Axis] 2026 Unrecorded Unconditional Purchase Obligation, to be Paid, Year Two PPACA Income Tax Deferral Medicare Part D Regulatory Asset [Member] Discloses the amount of regulatory asset arising from the deferral of the retail portion of a tax charge taken in 2010 resulting from the Patient Protection and Affordable Care Act of 2010 (PPACA). Total Lease Payments Due Finance Lease, Liability, to be Paid Prepayments and Other Prepayments and other Other Assets, Current Accounts Receivable Accounts Receivable [Policy Text Block] Equity Issuance (in shares) Equity issuance other (in shares) Stock Issued During Period, Shares, Other Boswell Unit 4 Boswell Unit 4 [Member] Boswell Unit 4 [Member] Capitalized share-based compensation costs Share-Based Payment Arrangement, Amount Capitalized Total Operating Expenses Costs and Expenses Net loss Net Loss (Gain) Net Gain Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Cash Contributions to Defined Benefit Pension Plans Payment for Pension Benefits 2027 Unrecorded Unconditional Purchase Obligation, to be Paid, Year Three Diluted Earnings Per Share, Diluted [Abstract] Rate Type [Axis] Rate Type [Axis] Rate Type [Axis] including categories like electric rates, natural gas rates, water rates, etc. Sale of Renewable Development Projects Sale of Renewable Development Projects [Member] Sale of Renewable Development Projects Geographical [Axis] Geographical [Axis] 2029 Lessee, Operating Lease, Liability, to be Paid, Year Five Long-term PSA Long-term PSA [Member] Revenue Recognized From Long-term PSAs Weighted Average Discount Rate: Leases, Weighted Average Discount Rate [Abstract] Leases, Weighted Average Discount Rate 2024 Minnesota General Rate Case 2024 Minnesota General Rate Case [Member] 2024 Minnesota General Rate Case Financing renewal term Debt Instrument, Renewal Term Renewal term for a debt instrument disclosing for what period of time after maturity the instrument may be extended. Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Employee Stock Purchase Plan (in shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans Other Non-Current Assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Prior Service Cost Prior Service Cost Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax Percentage of principal amount prepaid Debt Instrument, Prepayment, Percentage Of Principal Amount Prepaid Debt Instrument, Prepayment, Percentage Of Principal Amount Prepaid Cash, Cash Equivalents and Restricted Cash at Beginning of Period Cash, Cash Equivalents and Restricted Cash at End of Period Cash, Cash Equivalents and Restricted Cash on the Consolidated Statement of Cash Flows Cash and Cash Equivalents Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents Income Taxes Deferred Income Tax Charge [Member] Thereafter Finance Lease, Liability, To Be Paid, Due After Year Five Finance Lease, Liability, To Be Paid, Due After Year Five Unrecognized compensation cost Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Net (Gain) Loss Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax Long-term Contract for Purchase of Electric Capacity [Domain] Long-term Contract for Purchase of Electric Capacity [Domain] Long-term Contract for Purchase of Electric Capacity [Domain] Current Assets Assets, Current [Abstract] Consolidation Items [Axis] Consolidation Items [Axis] Cost Recovery Riders Regulatory Clause Revenues, under-Recovered [Member] Accrued interest Unrecognized Tax Benefits, Interest on Income Taxes Accrued Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Other Non-Current Liabilities Equity Method Investment, Summarized Financial Information, Other Non-Current Liabilities Equity Method Investment, Summarized Financial Information, Other Non-Current Liabilities Product and Service [Domain] Product and Service [Domain] Trade Accounts Receivable SEC Schedule, 12-09, Allowance, Credit Loss [Member] Awarded (in usd per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Actual Return on Plan Assets Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held Terminal growth rate - input for goodwill analysis Terminal Growth Rate - Input for Goodwill Analysis Terminal Growth Rate - Input for Goodwill Analysis New Energy Solar Energy Facilities New Energy Solar Energy Facilities [Member] New Energy Solar Energy Facilities Proceeds from legal settlements, gross Proceeds From Legal Settlements, Gross Proceeds From Legal Settlements, Gross Security Exchange Name Security Exchange Name Lease Contractual Term [Domain] Lease Contractual Term [Domain] State Current State and Local Tax Expense (Benefit) Alloy Parent Alloy Parent [Member] Alloy Parent Gain From Legal Settlements - after-tax Gain From Legal Settlements After Tax Gain From Legal Settlements After Tax Other Other Assets, Miscellaneous, Noncurrent Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Equity issuance program shares available for issuance (in shares) Equity Issuance Program Shares Available for Issuance The number of shares of common stock that remain available for issuance under the equity issuance program (KCCI distribution agreement). Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis Fair Value, Nonrecurring [Member] Number of Shares Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward] Boswell Units 1 and 2 Net Plant and Equipment Boswell 1 & 2 [Member] Boswell 1 & 2 [Member] Subsequent Events Subsequent Events, Policy [Policy Text Block] Generation Electricity Generation Plant, Non-Nuclear [Member] Common stock, shares issued (in shares) Common Stock, Shares, Issued 2025-01-01 2025-01-01 [Member] 2025-01-01 Amortization of (Loss) Gain Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax Entity [Domain] Entity [Domain] PIE Shares PIE Shares [Member] PIE Shares Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Concentration risk Concentration Risk, Percentage Granted, grant date fair value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Total Grant Date Fair Value The total grant date fair value of equity-based awards other than options, granted during the period. Authorized return on equity Public Utilities, Approved Return on Equity, Percentage Estimated Minimum Annual Payments for Certain Long-Term Commitments Unrecorded Unconditional Purchase Obligations Disclosure [Table Text Block] Other – Non-utility Other Revenue Not from Contract with Customer, Other Production Tax Credits Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount Residual value of leased asset Residual Value of Leased Asset Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Accumulated Depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment U.S. Small-cap U.S. Small Cap [Member] Equity Securities, U.S. Small Cap [Member] Manufactured Gas Plant Manufactured Gas Plant - Current Manufactured Gas Plant - Current Common stock, shares authorized (in shares) Common Stock, Shares Authorized Acquisitions of Subsidiaries – Net of Cash and Restricted Cash Acquired Payments to Acquire Businesses, Net of Cash Acquired Power Purchase Agreements [Line Items] Long-Term Contract for Purchase of Electric Power [Line Items] Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Supplemental Statement of Cash Flows Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Entity Voluntary Filers Entity Voluntary Filers Net Loss Attributable to Non-Controlling Interest Temporary Equity, Net Income Amortization of (Gain) Loss Defined Benefit Plan, Amortization of Gain (Loss) Materials and Supplies Inventory, Supplies, Net of Reserves PSAs Power Purchase Agreement - Current Liability The fair value adjustment for the price of power per MW at market rates compared to those at contract rate at the time of acquisition through the end of the contract term present valued to acquisition date resulting in a current liability. Balance Sheet Location [Axis] Statement of Financial Position Location, Balance [Axis] Interest Expense Interest Expense Interest Expense, Nonoperating Deferred Income Tax Expense (Benefit) Total Deferred Income Tax Expense (Benefit) Deferred Income Tax Expense (Benefit) Property, Plant and Equipment Property, Plant and Equipment Disclosure [Text Block] Discount Rate Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate Unrecognized Tax Benefits Income Tax Uncertainties, Policy [Policy Text Block] Irrevocable Grantor Trust Trust for Benefit of Employees [Member] 6.18% Senior Unsecured Notes Due September 2034 6.18% Senior Unsecured Notes Due September 2034 [Member] 6.18% Senior Unsecured Notes Due September 2034 Number of states contributed to downwind states’ challenges in attaining or maintaining ozone NAAQS Accrual for Environmental Loss Contingencies, Number Of States Contributed To Downwind Challenges in Maintaining Ozone NAAQS Accrual for Environmental Loss Contingencies, Number Of States Contributed To Downwind Challenges in Maintaining Ozone NAAQS Short-term debt - outstanding Debt, Current Recurring Fair Value Measures Fair Value, Recurring [Member] Total Trade Accounts Receivable Accounts Receivable, after Allowance for Credit Loss, Current U.S. Mid-cap Growth U.S. Mid-Cap Growth [Member] Equity Securities, U.S. Mid-Cap Growth [Member] Total Long-Term Debt Long-Term Debt Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Solar project, generating production (MW) Solar Project, Generating Production Solar Project, Generating Production Fair Value, Beginning of Year Fair Value, End of Year Fair Value of Assets Defined Benefit Plan, Plan Assets, Amount Long-term debt maturing thereafter Long-Term Debt, Maturity, after Year Five Billed Accounts Receivable, before Allowance for Credit Loss, Current Provision (Payments) for Interim Rate Refund Provision (Payments) for Interim Rate Refund Provision (Payments) for Interim Rate Refund Fair Value of Financial Instruments [Table] Fair Value, by Balance Sheet Grouping [Table] Restricted Cash included in Prepayments and Other Restricted Cash, Current % Ownership Jointly Owned Utility Plant, Proportionate Ownership Share Partnership Basis Differences Deferred Tax Liabilty, Partnership Basis Differences Deferred Tax Liability, Partnership Basis Differences Ppa annual debt service obligation Long-term Contract for Purchase of Electric Power, Annual Minimum Debt Service Payment Required, Obligation (Percentage) Long-term Contract for Purchase of Electric Power, Annual Minimum Debt Service Payment Required, Obligation (Percentage) Largest Customer Largest Customer [Member] Largest Customer [Member] Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Oconto Electric Cooperative Power Sales Agreement Oconto Electric Cooperative Power Sales Agreement [Member] Oconto Electric Cooperative Power Sales Agreement Actual indebtedness to total capitalization ratio Debt Instrument, Actual Indebtedness to Total Capital Ratio Actual indebtedness to total capital ratio required to be maintained by most restrictive financial covenant. Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Accumulated Net Periodic Benefit Cost in Excess of Contributions Accumulated Contributions in Excess of Net Periodic Benefit Cost (Prepaid Pension Asset) Accumulated Contributions in Excess of Net Periodic Benefit Cost (Prepaid Pension Asset) Nemadji Trail Energy Center Nemadji Trail Energy Center [Member] Nemadji Trail Energy Center [Member] Defined benefit pension and other postretirement benefit plans, income tax expense (benefit) Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax Document Annual Report Document Annual Report Bond interest rate Community Development District Obligation, Bond Interest Rate Interest rate of capital improvement revenue and special assessment bonds used to fund real estate development projects. Amortization of PSAs Amortization of Power Purchase Agreements The amount of income recognized in the current period that reflects income associated with the reduced liability of the PPAs acquired in a business acquisition. As noncash income, this element is subtracted from net income when calculating cash provided by or used in operations using the indirect method. 2027 Finance Lease, Liability, to be Paid, Year Three Awarded (in shares) Awarded (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Distributed solar project, generating production (MW) Distributed Solar Project, Generating Production Distributed Solar Project, Generating Production Long-term Contract for Purchase of Electric Power [Domain] Long-Term Contract for Purchase of Electric Power [Domain] Valuation and Qualifying Accounts and Reserves [Roll Forward] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] 4.54% Series Due 2032 4.54% Series Due 2032 [Member] 4.54% Series Due 2032 Liabilities Liabilities [Abstract] Generating capacity (MW) Anticipated Additional Generating Capacity (MW) Anticipated Additional Generating Capacity (MW) Operating Revenue Revenues [Abstract] Unamortized Investment Tax Credits Accumulated Deferred Investment Tax Credit Fair Value Fair Value Measurement, Policy [Policy Text Block] Acquisitions Business Combination Disclosure [Text Block] Current Fiscal Year End Date Current Fiscal Year End Date Balance at Beginning of Period Balance at End of Period SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount Less: Imputed Interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Total Regulatory Assets [Domain] Regulatory Asset [Domain] PEO Name PEO Name Award Type [Domain] Award Type [Domain] Great River Energy Power Sales Agreement (Expires May 2025) Great River Energy Power Sales Agreement (expires May 2025) [Member] Great River Energy Power Sales Agreement (expires May 2025) Other Power Suppliers Other Power Suppliers [Member] Other Power Suppliers Sales Channel [Member] Armenia Mountain Senior Secured Notes 3.26% Due 2024 Armenia Mountain Senior Secured Notes 3.26% Due 2024 [Member] Armenia Mountain Senior Secured Notes 3.26% Due 2024 [Member] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Defined Benefit Pension and Other Postretirement Benefit Plans Non-Current Liabilities Liability, Defined Benefit Plan, Noncurrent Regulatory Liabilities Regulatory liability Total Non-Current Regulatory Liabilities Regulatory Liability, Noncurrent Non-PEO NEO Non-PEO NEO [Member] Total Assets Acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets Finance Lease Liabilities Finance Lease, Liability, Noncurrent Bond term Community Development District Obligation, Bond Term, in Years Term (in years) of capital improvement revenue and special assessment bonds used to fund real estate development projects. Accounts Receivable Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] 2024 Wisconsin General Rate Case 2024 Wisconsin General Rate Case [Member] 2024 Wisconsin General Rate Case Pension and Other Postretirement Benefit Plans Retirement Benefits [Text Block] Summary of Common Stock [Line Items] Class of Stock [Line Items] 3.20% Series Due 2026 ALLETE Bonds 3.20% Due July2026 [Member] ALLETE Bonds 3.20% Due July2026 [Member] Regulatory Liabilities [Axis] Regulatory Liability [Axis] Unbilled Unbilled Receivables, Current New Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Class of Stock [Axis] Class of Stock [Axis] ALLETE, Inc. ALLETE, Inc. [Member] -- None. No documentation exists for this element. -- Other Purchase Obligations Other Purchase Obligations [Member] Other Purchase Obligations [Member] 2028 Finance Lease, Liability, to be Paid, Year Four Name Measure Name Entity Interactive Data Current Entity Interactive Data Current Long-term Contract for Purchase of Energy [Domain] Long-term Contract for Purchase of Energy [Domain] [Domain] for Long-term Contract for Purchase of Energy [Axis] New Energy New Energy [Member] New Energy Equity Distributed Minnesota solar energy standard - overall mandate percentage Distributed Solar Energy Standard Mandate, Overall Mandate Percentage Distributed Solar Energy Standard Mandate, Overall Mandate Percentage Land and Other Land and Other [Member] Land and Other [Member] Revenue collection period following the annual period it is recognized Revenue Collection Period Following the Annual Period it is Recognized Revenue Collection Period Following the Annual Period it is Recognized Number of operating segments Number of Operating Segments Dividend payable percentage limit Debt Instrument, Dividend Payable Percentage Limit Debt Instrument, Dividend Payable Percentage Limit Thereafter Unrecorded Unconditional Purchase Obligation, to be Paid, after Year Five Recurring Fair Value Measures Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] 4.08% Series Due 2029 ALLETE Bonds 4.08% Due March 2029 [Member] ALLETE Bonds 4.08% Due March 2029 [Member] ALLETE Properties Real Estate Investments, Net Boswell Unit 3 Boswell Unit 3 [Member] Boswell Unit 3 Short-term debt - unamortized debt issuance costs Debt Issuance Costs, Current, Net Share-Based and ESOP Compensation Expense Share-Based Payment Arrangement, Noncash Expense Capital cost spent to date Capital Cost Spent to Date Capital cost spent to date for project. Total Deferred Income Tax Assets Deferred Tax Assets, Net of Valuation Allowance Oliver Wind I PPA Oliver Wind I PPA [Member] Long-term contract with an affiliate of NextEra Energy, Inc. for the purchase of electric power. Transmission Assets CapX2020 [Member] CapX2020 (all projects) [Member] Interest rate Debt Instrument, Interest Rate, Stated Percentage Corporate and Other / Eliminations Segment Reporting, Reconciling Item, Corporate Nonsegment [Member] Net Income Attributable to ALLETE Net Income (Loss) Available to Common Stockholders, Diluted Transmission Assets Jointly Owned Electricity Transmission and Distribution System [Member] Total Other Income (Expense) Nonoperating Income (Expense) Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Schedule II SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] Auditor Firm ID Auditor Firm ID Effective tax rate Effective Income Tax Rate Reconciliation, Percent Tenaska Tenaska [Member] Tenaska Energy, Inc. and Tenaska Energy Holdings, LLC [Member] Operating Income Operating Income Operating Income (Loss) Natural Gas-Fired Natural Gas Processing Plant [Member] Total Lease Liabilities Lease, Liability Lease, Liability Number of reportable segments Number of Reportable Segments Total Liabilities, Redeemable Non-Controlling Interest and Equity Total Liabilities and Members’ Equity Liabilities and Equity Agreement and Plan of Merger Subsequent Events [Text Block] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Fair Value Hierarchy and NAV [Axis] Defined Benefit Plan, Fair Value of Plan Assets by Measurement [Axis] Fair Value Hierarchy and NAV [Axis] Available-for-Sale Securities Marketable Securities, Policy [Policy Text Block] Generation Type [Axis] Generation Type [Axis] Generation Type [Axis] BNI Energy BNI Energy [Member] BNI Energy [Member] 4.98% Series Due 2033 4.98% Series Due 2033 [Member] 4.98% Series Due 2033 Aggregate amount of available-for-sale corporate and governmental debt securities maturing in five years or more Available-for-sale Securities, Debt Maturities, After Five Years, Fair Value Amount of available-for-sale debt securities at fair value maturing in after the fifth fiscal year following the latest fiscal year (maturing in five years or more). 2026 Finance Lease, Liability, to be Paid, Year Two Energy conservation and optimization plan goal, second fiscal year Energy Conservation and Optimization Plan Goal, Second Fiscal Year Energy Conservation and Optimization Plan Goal, Second Fiscal Year Regulated Operations [Abstract] Regulated Operations [Abstract] Annual additional revenue generated from requested final rate increase Public Utilities, Requested Rate Increase (Decrease), Amount Restricted Stock Units Share-Based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block] Operations and Significant Accounting Policies Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] 2022 Minnesota General Rate Review 2022 Minnesota General Rate Review [Member] 2022 Minnesota General Rate Review Underlying Security Market Price Change Underlying Security Market Price Change, Percent Expected Return on Plan Assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Individual: Individual [Axis] Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Inventories – Net Total Inventories – Net Inventory, Net Product and Service [Axis] Product and Service [Axis] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Consolidated Statement of Equity [Line Items] Statement [Line Items] Reclassification of Property, Plant and Equipment to Inventory Reclassification of Property, Plant and Equipment to Inventory Reclassification of Property, Plant and Equipment to Inventory Fuel Energy Related Inventory, Coal Operating Expenses Operating Expenses [Abstract] Net Identifiable Assets Acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Benefits Paid Defined Benefit Plan, Plan Assets, Benefits Paid Property, Plant and Equipment and Estimated Useful Lives of Property, Plant and Equipment Property, Plant and Equipment [Table Text Block] Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Fuel Adjustment Clause 2023 Fuel Adjustment Clause 2023 [Member] Fuel Adjustment Clause 2023 Consideration transferred Business Combination, Consideration Transferred Regulatory Assets and Liabilities Disclosure [Abstract] Regulatory Assets and Liabilities Disclosure [Abstract] Equity Method Investments [Roll Forward] Equity Method Investments [Roll Forward] Equity Method Investments Accounts Receivable Increase (Decrease) in Accounts and Other Receivables Senior Unsecured Notes 3.11% Due 2027 ALLETE Senior Unsecured Notes 3.11% Due 2027 [Member] ALLETE Senior Unsecured Notes 3.11% Due 2027 [Member] Derivatives Derivatives, Policy [Policy Text Block] Annual assessment Community Development District Obligation, Annual Assessment Amount of annual assessments based on ownership percentage of benefited property related to real estate development projects funded by municipal capital improvement revenue and special assessment bonds. Recurring Fair Value Measures - Activity in Level 3 Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Contract asset - noncurrent Contract with Customer, Asset, after Allowance for Credit Loss, Noncurrent Minimum Minimum [Member] Adoption Date Trading Arrangement Adoption Date Estimated capital expenditures, including past expenditures Estimated Capital Expenditures, Including Past Expenditures The estimated amount of certain capital expenditures related to environmental compliance, regulatory matters, or other commitments and/or contingencies. This estimate includes expenditures expected in future periods and expenditures made through the end of the current period. Other receivables Other Receivables Maximum conversion window Common Stock, Convertible, Maximum Conversion Window Common Stock, Convertible, Maximum Conversion Window Trade Accounts Receivable Receivables, Net, Current [Abstract] Draws outstanding Line of Credit, Current Bad Debt Expense Accounts Receivable, Credit Loss Expense (Reversal) Information for Pension Plans with an Accumulated Benefit Obligation in Excess of Plan Assets Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Table Text Block] Business Segments [Axis] Segments [Axis] Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Statutory Federal Income Tax Rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Short-term and long-term debt - carrying amount Long-term debt Long-Term Debt, Gross Exercise Price Award Exercise Price Deferred Tax Assets and Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Generating Facility Axis [Axis] Generating Facility [Axis] Name of generating unit or facility Trend Rate Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year Arrangement Duration Trading Arrangement Duration State NOL Carryforwards Operating Loss Carryforwards Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax ALLETE Equity Equity, Attributable to Parent [Abstract] Interest and Investment Income Interest and Investment Earnings [Member] Interest and Investment Earnings [Member] Long-term investments Long-Term Investments Regulatory Assets Deferred Tax Liabilities, Regulatory Assets Long-term Contract with Customer Long-Term Contract with Customer [Member] Number of states operated in Number Of States Operated In Number Of States Operated In Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Fair Value Transfers Fair Value Transfer, Policy [Policy Text Block] Total Lease Obligations Finance Lease, Liability All Individuals All Individuals [Member] Power Sales Agreements Power Purchase Agreements, Deferred Tax Asset Power Purchase Agreements, Deferred Tax Asset Guarantee Entity and Type [Domain] Guarantee Entity and Type [Domain] Guarantee Entity and Type [Domain] SWL&P First Mortgage Bonds 4.14% Series Due 2048 SWL&P First Mortgage Bonds 4.14% Series Due 2048 [Member] SWL&P First Mortgage Bonds 4.14% Series Due 2048 [Member] Renewable Energy Energy Facilities Under Development Other Inventory, Gross Proceeds from issuance of first mortgage bond Proceeds from Issuance of First Mortgage Bond Contract with Customer, Duration [Domain] Contract with Customer, Duration [Domain] Income Taxes [Abstract] Income Tax Disclosure [Abstract] Deferred Income Tax Assets Deferred Tax Assets, Net of Valuation Allowance [Abstract] Other Total Other Income (Expense) - Other Other Nonoperating Income (Expense) Postretirement Health and Life Postretirement Health and Life Obligation and Funded Status Other Postretirement Benefits Plan [Member] Schedule of Regulatory Assets and Liabilities Schedule Of Regulatory Assets And Liabilities [Table Text Block] Schedule Of Regulatory Assets And Liabilities Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Long-Term Finance Receivables Financing Receivable, Held-for-Investment [Policy Text Block] Boswell Unit 4 Jointly Owned Electricity Generation Plant [Member] Other Expense Equity Method Investment, Summarized Financial Information, Other Expense The amount of other expense reported by an equity method investment of the entity. Changes in Regulatory and Other Non-Current Assets Increase (Decrease) in Other Noncurrent Assets Deferred Revaluation – Net of Federal Income Tax Benefit Effective Income Tax Rate Reconciliation, Deferred Revaluation - Net of Federal Income Tax Benefit Effective Income Tax Rate Reconciliation, Deferred Revaluation - Net of Federal Income Tax Benefit Deferred Gain Deferred Tax Liabilities - Deferred Gain Deferred Tax Liabilities - Deferred Gain Environmental remediation liability Environmental Remediation Liability Environmental Remediation Liability Change in Plan Assets Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract] Current Liabilities Liability, Defined Benefit Plan, Current Assets Assets, Fair Value Disclosure [Abstract] Percentage of total regulated utility k wh sales Percentage Of Total Regulated Utility kWh Sales Percentage Of Total Regulated Utility kWh Sales Tax credit carryforward, valuation allowance Tax Credit Carryforward, Valuation Allowance Related Party [Domain] Related and Nonrelated Parties [Domain] Glen Ullin Energy Center Glen Ullin Energy Center [Member] Glen Ullin Energy Center [Member] Total Liabilities Assumed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities Deferred Income Taxes Deferred Income Tax Liabilities, Net Long-Term Debt Due Within One Year Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Long-Term Debt Defined Benefit Pension and Other Postretirement Benefit Plans Net of Income Tax Expense (Benefit) of X.X, $2.4 and $(0.1) Defined Benefit Pension and Other Postretirement Plans Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Federal Deferred Federal Income Tax Expense (Benefit) Cash, Cash Equivalents and Restricted Cash Cash and Cash Equivalents, Policy [Policy Text Block] 5.99% Series Due 2027 5.99% Series Due 2027 [Member] First Mortgage Bonds, 5.99% Series Due 2027 [Member] Equity Issuance Costs Payments of Stock Issuance Costs Bonds Fair Value Disclosure, off-Balance-Sheet Risks, Face Amount, Liability (Gain) / Loss on Investments and Property, Plant and Equipment Gain (Loss) on Disposition of Other Assets Change in Benefit Obligation [Roll Forward] Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Impairment of long-lived assets held-for-use Impairment, Long-Lived Asset, Held-for-Use Measure: Measure [Axis] Depreciation Depreciation, Depletion, and Amortization [Policy Text Block] Investment Tax Credits Effective income Tax Rate Reconciliation - Investment Tax Credits Effective income Tax Rate Reconciliation - Investment Tax Credits Investments Investments [Abstract] ECO Triennial Filing ECO Triennial Filing [Member] ECO Triennial Filing Equity Issuance (in shares) Stock Issued During Period, Shares, New Issues Taconite Harbor Taconite Harbor Energy Center [Member] Taconite Harbor Energy Center 2025 Defined Benefit Plan, Expected Future Benefit Payment, Year One Entity Emerging Growth Company Entity Emerging Growth Company Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Total Fair Value of Liabilities Liabilities, Fair Value Disclosure Long-term debt maturing in 2029 Long-Term Debt, Maturity, Year Five 2.65% Senior Notes Due September 10, 2025 2.65% Senior Notes Due September 10, 2025 [Member] 2.65% Senior Notes Due September 10, 2025 Customer Type [Domain] Customer Type [Domain] Customer Type [Domain] Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Contracts with Customers – Utility Regulated Operating Revenue Accumulated Benefit Obligation Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation Finance Lease Other Non-Current Assets Finance Lease, Right-of-Use Asset, after Accumulated Amortization Total Equity [Domain] Equity Component [Domain] Equity Component [Domain] International International [Member] Equity Securities, International [Member] NOL and Tax Credit Carryforwards [Table] NOL and Tax Credit Carryforwards [Table] NOL and Tax Credit Carryforwards [Table] Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract] Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents [Abstract] Proceeds from Sale of Available-for-sale Securities Cash Proceeds From Sale Of Available-For-Sale Securities Cash Proceeds From Sale Of Available-For-Sale Securities Employer Contribution (Withdrawal) Defined Benefit Plan, Plan Assets, Withdrawal By Employer Defined Benefit Plan, Plan Assets, Withdrawal By Employer Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Entity Shell Company Entity Shell Company Entity Incorporation, State Entity Incorporation, State or Country Code 2028 Defined Benefit Plan, Expected Future Benefit Payment, Year Four SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] Guarantor Obligations by Nature [Axis] Guarantor Obligations, Nature [Axis] Consolidated Statement of Equity [Table] Statement [Table] Measurement Frequency [Domain] Measurement Frequency [Domain] Counterparty Name [Axis] Counterparty Name [Axis] Defined Benefit Pension and Other Postretirement Plan Expense (Benefit) Pension and Other Postretirement Benefits Expense (Reversal of Expense), Noncash Consolidation Items [Domain] Consolidation Items [Domain] Real Estate Real Estate [Member] SWL&P SWL&P [Member] Superior, Water, Light and Power [Member] ALLETE Clean Energy ALLETE Clean Energy [Member] ALLETE Clean Energy [Member] Approximate reduction in pretax income for FERC proposal to limit incentive adder, ALLETE's proportionate share Approximate Reduction in Pretax Income for FERC Proposal to Limit Incentive adder, ALLETE's Proportionate Share Approximate Reduction in Pretax Income for FERC Proposal to Limit Incentive adder, ALLETE's Proportionate Share 5.05% Series Due 2044 ALLETE Bonds 5.05% Due July2044 [Member] ALLETE Bonds 5.05% Due July2044 [Member] Cash Paid During the Period for Interest – Net of Amounts Capitalized Interest Paid, Excluding Capitalized Interest, Operating Activities Level 1 Fair Value, Inputs, Level 1 [Member] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Litigation settlement, amount awarded from other party, prejudgment interest Litigation Settlement, Amount Awarded From Other Party, Prejudgment Interest Prejudgment Interest From Legal Settlements Annual Debt Service Period [Axis] Annual Debt Service Period [Axis] Annual Debt Service Period [Axis] Jointly-Owned Facilities and Assets Jointly-Owned Electric Facility [Text Block] Jointly-Owned Electric Facility [Text Block] Total Current Assets Current Assets Assets, Current Receivables from large power customers Accounts Receivable, before Allowance for Credit Loss Generating Facility [Domain] Generating Facility [Domain] Generating Facility [Domain] Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Senior Notes Senior Notes [Member] Surety Bonds Surety Bond [Member] Noncash Investing and Financing Activities Noncash Investing and Financing Items [Abstract] Employee Benefits and Compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation Long-term debt maturing in 2027 Long-Term Debt, Maturity, Year Three Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Employer contribution Employer Contribution Defined Benefit Plan, Plan Assets, Contributions by Employer Quarterly Financial Data (Unaudited) Quarterly Financial Information [Text Block] Generation Type [Domain] Generation Type [Domain] [Domain] for Generation Type [Axis] Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Income Tax Expense Income Tax Disclosure [Text Block] 2028 Lessee, Operating Lease, Liability, to be Paid, Year Four South Peak South Peak [Member] South Peak [Member] Purchase price accounting - after tax Purchase Price Accounting After Tax Purchase Price Accounting After Tax Capital Purchase Obligations Capital Addition Purchase Commitments [Member] Transmission [Domain] Transmission [Domain] Name of transmission investment. Number of complaints Number Of Complaints Filed Number Of Complaints Filed BNI Energy Reclamation Liability BNI Coal Reclamation Liability [Member] Reclamation liability for closing costs associated with BNI Coal mine and mine facilities. Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Retail Customers Retail [Member] Unamortized Discount and Premium on Debt Debt, Policy [Policy Text Block] Operating Lease Operating Lease, Weighted Average Discount Rate, Percent Cash provided (used in) by Financing Activities Net Cash Provided by (Used in) Financing Activities Executive Long-Term Incentive Compensation Plan Executive Plan [Member] Stock based, long-term incentive compensation, Executive Plan [Member] Distributions to Non-Controlling Interest Temporary Equity, Distributions To Non-Controlling Interest Temporary Equity, Distributions To Non-Controlling Interest Credit Facility [Axis] Credit Facility [Axis] 4.08% Series Due 2042 ALLETE Bonds 4.08% Due July2042 [Member] ALLETE Bonds 4.08% Due July2042 [Member] Non-Controlling Interest Effective Income Tax Rate Reconciliation, Noncontrolling Interest Income (Loss), Amount Short-term and long-term debt - fair value Long-Term Debt, Fair Value Entity Registrant Name Entity Registrant Name Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Depreciation and Amortization Depreciation and Amortization Depreciation, Depletion and Amortization Revenue from cost recovery riders Regulated Operating Revenue, Other State Deferred State and Local Income Tax Expense (Benefit) Fair Value as of Grant Date Award Grant Date Fair Value Customer Concentration Risk Customer Concentration Risk [Member] Non-Current Assets Assets for Plan Benefits, Defined Benefit Plan Level 2 Fair Value, Inputs, Level 2 [Member] Equity Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Geographical [Domain] Geographical [Domain] Capitalized contract cost, amortization Capitalized Contract Cost, Amortization Minnesota solar energy standard - overall mandate percentage Solar Energy Standard Mandate, Overall Mandate Percentage Minnesota's solar energy mandate for total retail electric sales, excluding sales to certain industrial customers, by the end of 2020. Common Stock Issued Common stock issued Stock Issued During Period, Value, New Issues Renewable Tax Credit Sales Renewable Tax Credit Sales Renewable Tax Credit Sales Principles of Consolidation Consolidation, Policy [Policy Text Block] Restatement Determination Date: Restatement Determination Date [Axis] Amortization of the Remeasurement of Deferred Income Taxes Amortization From The Remeasurement Of Deferred Income Taxes For Equity Method Investments Amortization From The Remeasurement Of Deferred Income Taxes For Equity Method Investments Title of 12(b) Security Title of 12(b) Security Concentration Risk Type [Axis] Concentration Risk Type [Axis] Common Stock Without Par Value, 80.0 Shares Authorized, 57.9 and 57.6 Shares Issued and Outstanding Common Stock, Value, Issued Document Financial Statement Error Correction Document Financial Statement Error Correction [Flag] Expected employer contributions in 2025 Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year Share-based Payment Arrangement [Abstract] Share-Based Payment Arrangement [Abstract] Non-Jurisdictional Land Sales Non-Jurisdictional Land Sales [Member] Non-Jurisdictional Land Sales Beginning obligation Ending obligation Asset Retirement Obligation Calpine Corporation Calpine Corporation [Member] Calpine Corporation Number of states restrictions on fossil-fuel fired power plants Accrual for Environmental Loss Contingencies, Number Of States Restricted On Fossil-Fuel Fired Power Plants Accrual for Environmental Loss Contingencies, Number Of States Restricted On Fossil-Fuel Fired Power Plants Output being purchased - electric capacity (MW) Long-term Contract for Purchase of Electric Capacity (MW) Long-term Contract for Purchase of Electric Capacity (MW) Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Regulatory Assets Regulatory asset Total Non-Current Regulatory Assets Regulatory Asset, Noncurrent Participant Contributions Defined Benefit Plan Contributions by Plan Participants, Excluding Key Employees Defined Benefit Plan Contributions by Plan Participants, Excluding Key Employees Available-for-sale – Equity Securities Equity Securities, FV-NI, Noncurrent Total Current Regulatory Liabilities Regulatory Liability, Current Other Deferred Tax Assets, Other Summary of Common Stock Schedule of Common Stock Outstanding Roll Forward [Table Text Block] Customer Class [Domain] Customer Class [Domain] [Domain] for Customer Class [Axis] description of customer types or classes Basin Electric Cooperative PSA June 2022 - May 2023 Basin Electric Cooperative PSA June 2022 - May 2023 [Member] Basin Electric Cooperative PSA June 2022 - May 2023 [Member] Financing Activities Net Cash Provided by (Used in) Financing Activities [Abstract] 2029 Defined Benefit Plan, Expected Future Benefit Payment, Year Five State Income Taxes – Net of Federal Income Tax Benefit Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Regulatory liabilities Regulatory Liability Investment Tax Credits Investment Tax Credits Subject to Refund [Member] Investment Tax Credits Subject to Refund [Member] Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Total Deferred Income Tax Liabilities Deferred Tax Liabilities, Gross Basic Earnings Per Share of Common Stock (in usd per share) Earnings Per Share (in usd per share) Earnings Per Share, Basic Regulatory Differences – Excess Deferred Tax Benefit Effective Income Tax Rate Reconciliation, Regulatory Differences Regulatory Differences contributing to difference in effective tax rate to federal statutory rate. Proceeds from Issuance of Common Stock Proceeds from Issuance of Common Stock Cash and Cash Equivalents Cash and Cash Equivalents [Member] Operating Cash Flows From Operating Leases Operating Lease, Payments Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] 3.86% Series Due 2030 ALLETE Bonds 3.86% Due September 2030 [Member] ALLETE Bonds 3.86% Due September 2030 [Member] Current Liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Actual Plan Asset Allocations Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage Residential Residential [Member] Revenue Recognized From Residential Customers Property, Plant and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Total Current Liabilities Current Liabilities Liabilities, Current Balance, Beginning of Period Total Redeemable Non-Controlling Interest Temporary Equity, Carrying Amount, Attributable to Parent Distributed ATC Earnings Proceeds from Equity Method Investment, Distribution Requested equity ratio Public Utilities, Requested Equity Capital Structure, Percentage Equity Method Investment, Nonconsolidated Investee [Domain] Equity Method Investment, Nonconsolidated Investee [Domain] Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Proceeds from Non-Controlling Interest in Subsidiaries – Net of Issuance Costs Noncontrolling Interest, Increase from Subsidiary Equity Issuance Recurring Fair Value Measures Fair Value, Assets Measured on Recurring Basis [Table Text Block] 5.94% Senior Unsecured Notes Due September 2029 5.94% Senior Unsecured Notes Due September 2029 [Member] 5.94% Senior Unsecured Notes Due September 2029 Fuel Adjustment Clause Fuel Adjustment Clause [Member] Fuel Adjustment Clause Proceeds from legal settlements Proceeds from Legal Settlements Oconto Electric Cooperative Oconto Electric Cooperative [Member] Oconto Electric Cooperative 5.69% Series Due 2036 5.69% Series Due 2036 [Member] First Mortgage Bonds, 5.69% Series Due 2036 [Member] Acquisitions Business Combinations Policy [Policy Text Block] Equity Investments Equity Method Investments and Joint Ventures Disclosure [Text Block] Regulatory Matters [Line Items] Public Utilities, General Disclosures [Line Items] Energy generation owned, operated or developed (MW) Generating Capacity Owned, Operated Or Developed (MW) Generating Capacity Owned, Operated Or Developed (MW) Discount Rate Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Litigation settlement, amount awarded from other party, pre tax gain Litigation Settlement, Amount Awarded From Other Party, Pre Tax Gain Litigation Settlement, Amount Awarded From Other Party, Pre Tax Gain Total Operating Revenue Revenue Operating Revenue Revenues Aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year to less than three years Available-for-sale Securities, Debt Maturities, After One Year Through Three Years, Fair Value Amount of available-for-sale debt securities at fair value maturing after the first fiscal year through the third fiscal year following the latest fiscal year (maturing in more than one year to less than three years). Contracts with Customers – Non-utility Unregulated Operating Revenue Large power customer contracts Large Power Customer Contracts Large Power Customer Contracts Employee Stock and Incentive Plans Share-Based Payment Arrangement [Text Block] Municipal Municipal [Member] Municipal Sales Channel Entity Address, City Entity Address, City or Town Proceeds from Issuance of Short-Term and Long-Term Debt Proceeds from Issuance of Long-Term Debt Leases Lessee, Leases [Policy Text Block] Customer Type [Axis] Customer Type [Axis] Customer Type [Axis] Asset Retirement Obligations Asset Retirement Obligation [Policy Text Block] Total Share-Based Compensation Expense Share-Based Payment Arrangement, Expense Forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period Weighted Average Assumptions Used to Determine Benefit Obligation Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract] Business Acquisition [Axis] Business Acquisition [Axis] Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Finance Finance Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract] Manitoba Hydro PPA (Expires 2040) Manitoba Hydro PPA (expires 2040) [Member] Manitoba Hydro PPA (expires 2040) [Member] MPUC MPUC [Member] Minnesota Public Utilities Commission [Member] Liabilities: Liabilities, Fair Value Disclosure [Abstract] Total Lease Right-of-use Assets Lease, Right-of-Use Asset Lease, Right-of-Use Asset Document Fiscal Year Focus Document Fiscal Year Focus Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Regulatory Assets and Liabilities [Line Items] Regulatory Assets and Liabilities [Line Items] Regulatory Assets and Liabilities [Line Items] Total Fair Value of Assets Assets, Fair Value Disclosure Other Other Accrued Liabilities, Current Income Statement Data Income Statement Data [Abstract] Income Statement Data FERC FERC [Member] Federal Energy Regulatory Commission [Member] Document Period End Date Document Period End Date Proceeds from Non-Controlling Interest in Subsidiaries – Net of Issuance Costs Proceeds from Noncontrolling Interests Finance Lease Liabilities Less: Current Lease Obligations Finance Lease, Liability, Current Cash Equivalents Other Restricted Assets, Noncurrent Total Lease Payments Due Lessee, Operating Lease, Liability, to be Paid Obligation and Funded Status Schedule of Net Funded Status [Table Text Block] Beginning balance (in shares) Ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Income from Equity Investments – Net of Dividends Income (Loss) from Equity Method Investments, Net of Dividends or Distributions Insider Trading Arrangements [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Contract with Customer, Sales Channel [Domain] Contract with Customer, Sales Channel [Domain] Sale of Energy under PSA Sale of Energy under PSA [Member] Sale of Energy under PSA [Member] 2027 Lessee, Operating Lease, Liability, to be Paid, Year Three FERC authorized return on common equity FERC Authorized Return on Common Equity FERC Authorized Return on Common Equity Accumulated Benefit Obligation Defined Benefit Plan, Accumulated Benefit Obligation Power Purchase Agreements [Table] Regulated Operation, Long-Term Contract for Purchase of Electric Power [Table] Document Transition Report Document Transition Report PSCW PSCW [Member] Public Service Corporation of Wisconsin [Member] Accounts Receivable Business Combination, Acquired Receivable, Fair Value Gross Unrecognized Income Tax Benefits Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block] Operating Expense Equity Method Investment, Summarized Financial Information, Operating Expense The amount of the operating expense reported by an equity method investment of the entity. Recurring Fair Value Measurements [Table] Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis [Table] Fair Value, Recurring and Nonrecurring [Table] Customer [Domain] Customer [Domain] Entity Current Reporting Status Entity Current Reporting Status Retained Earnings Retained Earnings [Member] Other Non-Current Liabilities Other Noncurrent Liabilities [Table Text Block] Output being purchased - electric energy and capacity (MW) Long-term Contract for Purchase of Electric Energy and Capacity (MW) Long-term Contract for Purchase of Electric Energy and Capacity (MW) Unearned Grant Award (in usd per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Unearned Grant Award, Weighted Average Grant Date Fair Value Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Unearned Grant Award, Weighted Average Grant Date Fair Value (Per Share) Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] Number of customers Number of Customers Number of Customers Restricted Stock Units Restricted Stock Units (RSUs) [Member] Other Long-Term Debt, 2024 Weighted Average Rate 4.47% Due 2025 – 2051 Other Long-Term Debt [Member] Other long-term debt instruments not specifically identified elsewhere Non-Controlling Interest in Subsidiaries and Redeemable Non-Controlling Interest Consolidation, Subsidiaries or Other Investments, Consolidated Entities, Policy [Policy Text Block] Consolidated Statement of Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Executive Category: Executive Category [Axis] VEBA VEBA [Member] VEBA (Voluntary Employee Benefits Association trusts) [Member] Income Tax Expense Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Ppa counterparty total debt outstanding Long-Term Contract for Purchase of Electric Power, Amount of Long-Term Debt or Lease Obligation Outstanding Allowed indebtedness to total capitalization ratio Debt Instrument, Required Indebtedness to Total Capital Ratio Indebtedness to total capital ratio required to be maintained by most restrictive financial covenant. Minnesota solar energy standard - small scale solar mandate percentage Solar Energy Standard Mandate, Small Scale Solar Mandate Percentage Minnesota's solar energy mandate for small scale solar with photovoltaic devices with a nameplate capacity of 20 kilowatts or less by the end of 2020. Expressed as a percentage of the overall mandate. Company Selected Measure Name Company Selected Measure Name