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Consolidated Balance Sheet Unaudited Parentheticals - USD ($) shares in Millions, $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Accounts Receivable [Abstract]
Accounts Receivable (Less Allowance of $1.7 and $1.6)	$ 1.7	$ 1.6
Common Stock [Abstract]
Common stock, shares authorized (in shares)	80.0	80.0
Common stock, shares outstanding (in shares)	57.7	57.6
Common stock, shares issued (in shares)	57.7	57.6

Commitments, Guarantees and Contingencies	3 Months Ended
Commitments, Guarantees and Contingencies	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments, Guarantees and Contingencies	COMMITMENTS, GUARANTEES AND CONTINGENCIES Power Purchase and Sale 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. Our PPAs are summarized in Note 9. Commitments, Guarantees and Contingencies to the Consolidated Financial Statements in our 2023 Form 10-K, with additional disclosure provided in the following paragraphs. Square Butte PPA. As of March 31, 2024, Square Butte had total debt outstanding of $162.6 million. 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. Minnesota Power’s cost of power purchased from Square Butte during the three months ended March 31, 2024, was $22.9 million ($22.1 million for the same period in 2023). 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 $1.3 million ($1.3 million for the same period in 2023). Minnesota Power’s payments to Square Butte are approved as a purchased power expense for ratemaking purposes by both the MPUC and the FERC. Minnkota Power PSA. Minnesota Power has a PSA with Minnkota Power, which commenced in 2014. Under the PSA, 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, Minnesota Power sold to Minnkota Power approximately 41 percent in 2024 and 37 percent in 2023. 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 have been promulgated by both the EPA and state authorities over the past several years. Minnesota Power’s facilities are subject to additional 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 state and federal environmental regulations and requirements finalized, or to be finalized in the near future, 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 both 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. NOTE 6. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued) Environmental Matters (Continued) 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 our 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 fine particulate matter while retaining other existing primary and secondary standards such as those for coarse 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 potential NAAQS revisions cannot yet be estimated; however, costs could be material. Minnesota Power would seek recovery of additional costs through a rate proceeding. 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 within their state borders. 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 the state of Minnesota’s SIP. On July 5, 2023, the Eighth Circuit Court granted a stay of the SIP disapproval preventing the Good Neighbor Plan from taking effect in Minnesota. On March 28, 2024, the EPA issued a partial denial of several administrative reconsideration and stay petitions, including from the Minnesota coalition. 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. On February 21, 2024, the U.S. Supreme Court heard 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. NOTE 6. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued) Environmental Matters (Continued) 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 25, 2024, the EPA published a final rule to revise the existing 2012 MATS Rule, which regulates air emissions of hazardous air pollutants from coal- and oil-fired electric generating units (EGUs). The final rule eliminates certain MATS compliance flexibility, lowers the particulate emission standard for all coal-fired EGUs, and reduces the mercury emission standard for lignite-fired EGUs. The rule will become effective 60 days after publication in the Federal Register, with compliance beginning in 2027. The MATS regulation applies at Minnesota Power’s Boswell facility, which is currently well-controlled for these emissions and already complying with some of the new requirements. The Company is analyzing the new rule but anticipates that its impacts to Boswell may be minimal. However, compliance costs cannot yet be estimated, and recovery of any additional costs would be sought through a rate proceeding. 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 April 25, 2024, the EPA issued several final greenhouse gas regulations to establish emissions standards and guidelines for fossil fuel-fired electric generating units (EGUs) under Section 111 of the Clean Air Act (CAA). The final rules revise new source performance standards (NSPS) for new, modified and reconstructed EGUs (Section 111(b) of the CAA) and creates new emission guidelines for existing EGUs (Section 111(d) of the CAA). The action also officially repeals the predecessor regulation “Affordable Clean Energy Rule”, first issued in 2019 and later vacated in 2021. Compliance will be required beginning January 1, 2030 for existing sources, and upon commencing operation of new units. The 111(d) rule also requires states to submit plans to provide for the establishment, implementation and enforcement of standards of performance for existing sources. States must submit their plans to the EPA within 24 months after publication of the final emissions guidelines. The final 111 rules apply to several Company assets, including existing EGUs at the Boswell and Laskin facilities as well as the proposed combined cycle natural gas-fired generating facility, NTEC. The Company is reviewing the new rule, but anticipates compliance may require operational or planning adjustments. The state implementation plan process for Section 111(d) existing units will also be a factor in determining specific requirements and timing. We are unable to predict compliance costs at this time; 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 agencies for any wastewater discharged into navigable waters. We have obtained all necessary NPDES permits, including NPDES storm water permits for applicable facilities, to conduct our operations. NOTE 6. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued) Environmental Matters (Continued) 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. It set effluent limits and prescribed Best Available Control Technology (BACT) for several wastewater streams, including flue gas desulphurization (FGD) water, bottom ash transport water and coal combustion landfill leachate. In October 2020, the EPA published a final ELG Rule allowing re-use of bottom ash transport water in FGD scrubber systems with limited discharges related to maintaining system water balance. The rule set technology standards and numerical pollutant limits for discharges of bottom ash transport water 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 April 25, 2024, the EPA released a pre-publication version of a final ELG rule to update the 2020 ELGs. In the final rule, the EPA is revising ELGs for existing sources, including establishing zero discharge limitations for bottom ash transport water, FGD wastewater, and combustion residual leachate, and allowing states to set discharge limits for legacy wastewater in surface impoundments based on best professional judgment. 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 final ELG rule also establishes mercury and arsenic limitations for functionally equivalent discharges of leachate via groundwater to surface water. Compliance deadlines are determined by the applicable state permitting authority. Compliance deadlines could be required as soon as 60 days after the final rule is published in the Federal Register, but no later than December 31, 2029. Bottom ash transport and FGD wastewater ELGs are not expected to have a significant impact on Minnesota Power operations. Zero leachate discharge requirements have the potential to impact dewatering associated with the closed Taconite Harbor dry ash landfill and Laskin’s closed Cell E impoundment. New limitations for arsenic and mercury related to functionally equivalent (groundwater to surface water) discharges are not currently anticipated to impact Minnesota Power facilities. We estimate no additional material compliance costs for ELG bottom ash water 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 approved by the EPA in April 2024, 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 of 1976 regulates the management and disposal of solid and hazardous wastes. We are required to notify the EPA of hazardous waste activity and, consequently, 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. NOTE 6. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued) Environmental Matters (Continued) 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 additional 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. On April 25, 2024, the EPA finalized the CCR Legacy Impoundment Rule. The final rule 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 rule requires all regulated generating facilities to evaluate and identify 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. Additionally, the EPA finalized portions of the proposed CCR Part B Rule, which allows CCR Units to certify closure while conducting groundwater remediation activities. This rule is currently under review; however impacts to previously closed CCR Units at Boswell and Laskin are anticipated. 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, alternative liner demonstrations and other CCR regulatory revisions. Portions of the Part B rule addressing alternative liner equivalency standards were finalized in November 2020. Finalization of the remaining beneficial reuse requirements are 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 March 31, 2024, SWL&P has recorded a liability of approximately $1 million for remediation costs at this site. SWL&P has recorded the recovery of the remediation costs associated with the site as a regulatory asset as we expect recovery of these costs to be allowed by the PSCW. Other Matters. Letters of Credit, Surety Bonds and Other Indemnifications. We have multiple credit facility agreements in place that provide the ability to issue standby letters of credit to satisfy contractual security requirements across our businesses. As of March 31, 2024, we had $150.1 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. In April 2024, under the tax credit transferability provision of the Inflation Reduction Act, we entered into an agreement with a third party to sell a portion of our production tax credits. ALLETE has indemnified the third party for the value of production tax credits sold to date of approximately $14 million. Regulated Operations. As of March 31, 2024, we had $25.4 million outstanding in standby letters of credit at our Regulated Operations which are pledged as security to MISO, the NDPSC and state agencies. NOTE 6. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued) Other Matters (Continued) ALLETE Clean Energy. ALLETE Clean Energy is party to PSAs that expire in various years between 2024 and 2039. As of March 31, 2024, ALLETE Clean Energy has $80.6 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 March 31, 2024, 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. The Nobles 2 wind energy facility requires standby letters of credit as security for certain contractual obligations. As of March 31, 2024, ALLETE South Wind has $10.1 million outstanding in standby letters of credit, related to its portion of the security requirements relative to its ownership in Nobles 2. South Shore Energy. As of March 31, 2024, South Shore Energy had $29.7 million outstanding in standby letters of credit pledged as security in connection with the development of NTEC. 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.

Business Segments - Narrative (Details)	3 Months Ended
Business Segments - Narrative (Details)	Mar. 31, 2024 segment
Business Segments [Line Items]
Number of reportable segments	2
Regulated Operations
Business Segments [Line Items]
Number of operating segments	3

Subsequent Event - Agreement and Plan of Merger	3 Months Ended
Subsequent Event - Agreement and Plan of Merger	Mar. 31, 2024
Subsequent Events [Abstract]
Subsequent Event - Agreement and Plan of Merger	SUBSEQUENT EVENT – AGREEMENT AND PLAN OF MERGER On May 5, 2024, ALLETE entered into the Merger Agreement. Pursuant to the Merger Agreement, on the terms and subject to the conditions set forth therein, Alloy Merger Sub will merge with and into ALLETE, with ALLETE continuing as the surviving corporation in the Merger and becoming a subsidiary of Alloy Parent. Subject to the terms and conditions set forth in the Merger Agreement, which has been unanimously approved by the board of directors of ALLETE, at the effective time of the Merger (Effective Time), each share of common stock, without par value, of ALLETE (ALLETE common stock) issued and outstanding immediately prior to the Effective Time (other than shares of ALLETE common stock held by any holder who properly exercises dissenters’ rights under Minnesota law in respect of such shares and any shares of ALLETE common stock held by an affiliate of Alloy Parent) shall be converted into the right to receive $67.00 in cash, without interest (Merger Consideration). The aggregate equity value of the ALLETE common stock acquired by Parent will be approximately $3.9 billion as calculated as of May 5, 2024. In addition, at the Effective Time, each restricted stock unit with respect to ALLETE common stock subject to time-based vesting that is outstanding immediately prior to the Effective Time (RSU) will be cancelled and converted into a contingent right to receive an amount in cash, without interest, equal to the Merger Consideration, payable (i) in the case of such right converted from unvested RSUs, upon the same vesting conditions as applied to the corresponding RSU or (ii) in the case of such right converted from vested RSUs, as soon as reasonably practicable following the closing date of the Merger (the Closing Date). Each performance share award with respect to ALLETE common stock that is outstanding and unvested immediately prior to the Effective Time will be cancelled and converted into a right to receive, without interest, the Merger Consideration multiplied by the number of shares of ALLETE common stock subject to the award, determined based on attainment of the greater of target and actual performance as of the last business day immediately preceding the Closing Date. A pro rata portion (based on the elapsed portion of the performance period at that time) of the converted performance share awards will be paid out as soon as reasonably practicable following the Closing Date, with the remainder of the award being subject to time-vesting for the remainder of the applicable performance period. Further, purchase rights accumulated during the offering period in effect under the Company’s Employee Stock Purchase Plan (ESPP) immediately prior to closing will be automatically exercised into shares of ALLETE common stock no later than five business days prior to the Closing Date, and the ESPP will be terminated as of immediately prior to the Closing Date. Consummation of the Merger is subject to various closing conditions, including: (1) approval of the shareholders of the Company; (2) receipt of all required regulatory approvals without the imposition of a Burdensome Condition (as defined in the Merger Agreement); (3) absence of any law or order prohibiting the consummation of the Merger; (4) subject to materiality qualifiers, the accuracy of each party’s representations and warranties; (5) each party’s compliance in all material respects with its obligations and covenants under the Merger Agreement; and (6) the absence of a material adverse effect with respect to the Company. The Merger Agreement contains certain termination rights for ALLETE and Alloy Parent, which were described in a Current Report of Form 8-K filed by ALLETE on May 6, 2024. In the Merger Agreement, among other things, ALLETE has agreed, subject to certain exceptions, to, and to cause each of its subsidiaries to conduct its business in the ordinary course, consistent with past practice, from the date of the Merger Agreement until the Effective Time, and not to take certain actions prior to the closing of the Merger without the prior written consent of Alloy Parent (which consent shall not be unreasonably withheld, conditioned or delayed, except where ALLETE seeks Alloy Parent’s consent to enter into a material new line of business or cease operations of an existing material line of business). The Merger Agreement also provides that the Company may request that Alloy Parent purchase up to a total of $300 million of preferred stock of the Company in the second half of 2025, subject to certain parameters. If Alloy Parent declines to purchase the preferred stock, the Company will have the right to issue Company common stock up to certain limits.

Income Tax Expense - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Effective tax rate	9.70%	3.80%
Gross unrecognized tax benefits	$ 1.1		$ 1.1
Gross unrecognized tax benefits that would favorably impact effective income tax rate	$ 0.6

Business Segments - (Details) - USD ($) $ in Millions	3 Months Ended
Business Segments - (Details) - USD ($) $ in Millions	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Business Segments [Line Items]
Total Operating Revenue	$ 403.3	$ 564.9
Net Income Attributable to ALLETE	50.7	58.2
Assets	6,604.6		$ 6,656.4
Corporate and Other
Business Segments [Line Items]
Total Operating Revenue	403.3	564.9
Regulated Operations
Business Segments [Line Items]
Net Income Attributable to ALLETE	44.2	40.6
Assets	4,345.1		4,335.0
Regulated Operations \| Operating Segments
Business Segments [Line Items]
Total Operating Revenue	338.3	312.6
Regulated Operations \| Residential \| Operating Segments
Business Segments [Line Items]
Operating Revenue	51.5	49.4
Regulated Operations \| Commercial \| Operating Segments
Business Segments [Line Items]
Operating Revenue	49.7	47.7
Regulated Operations \| Municipal \| Operating Segments
Business Segments [Line Items]
Operating Revenue	9.0	8.9
Regulated Operations \| Industrial \| Operating Segments
Business Segments [Line Items]
Operating Revenue	159.5	144.9
Regulated Operations \| Other Power Suppliers \| Operating Segments
Business Segments [Line Items]
Operating Revenue	40.0	35.9
Regulated Operations \| Other \| Operating Segments
Business Segments [Line Items]
Operating Revenue	28.6	25.8
ALLETE Clean Energy
Business Segments [Line Items]
Net Income Attributable to ALLETE	3.8	8.5
Assets	1,580.0		1,594.1
ALLETE Clean Energy \| Operating Segments
Business Segments [Line Items]
Total Operating Revenue	19.1	201.5
ALLETE Clean Energy \| Long-term PSA \| Operating Segments
Business Segments [Line Items]
Operating Revenue	17.8	18.4
ALLETE Clean Energy \| Sale of Wind Energy Facilities \| Operating Segments
Business Segments [Line Items]
Operating Revenue	0.0	181.8
ALLETE Clean Energy \| Other \| Operating Segments
Business Segments [Line Items]
Operating revenue, other than customer revenue	1.3	1.3
Corporate and Other
Business Segments [Line Items]
Net Income Attributable to ALLETE	2.7	9.1
Assets	679.5		$ 727.3
Corporate and Other \| Corporate and Other
Business Segments [Line Items]
Total Operating Revenue	45.9	50.8
Corporate and Other \| Long-term Contract \| Corporate and Other
Business Segments [Line Items]
Operating Revenue	25.4	25.5
Corporate and Other \| Sale of Renewable Development Projects \| Corporate and Other
Business Segments [Line Items]
Operating Revenue	13.9	19.8
Corporate and Other \| Other \| Corporate and Other
Business Segments [Line Items]
Operating Revenue	$ 6.6	$ 5.5

Earnings Per Share and Common Stock (Tables)

3 Months Ended

Mar. 31, 2024

Earnings Per Share [Abstract]

Reconciliation of Basic and Diluted Earnings Per Share

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.


Three Months Ended March 31,		2024			2023
Reconciliation of Basic and Diluted		Dilutive			Dilutive
Earnings Per Share	Basic	Securities	Diluted	Basic	Securities	Diluted
Millions Except Per Share Amounts




Net Income Attributable to ALLETE	$50.7		$50.7	$58.2		$58.2
Average Common Shares	57.6	0.1	57.7	57.3	—	57.3
Earnings Per Share	$0.88		$0.88	$1.02		$1.02

Subsequent Event - Agreement and Plan of Merger - Narrative (Details) - Alloy Parent and Alloy Merger Sub - Forecast $ / shares in Units, $ in Millions	8 Months Ended
	Dec. 31, 2024 USD ($) $ / shares
Subsequent Event
Subsequent Event [Line Items]
Conversion price, cash (in usd per share) \| $ / shares	$ 67.00
Equity value of ALLETE common stock acquired	$ 3,900
Alloy Parent
Subsequent Event [Line Items]
Required amount to purchase of preferred stock	$ 300

Operations and Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Non-Controlling Interest Details [Line Items]
Goodwill	$ 154.9		$ 154.9
Net Loss Attributable to Non-Controlling Interest	$ (13.7)	$ (20.6)

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References + Details

- Definition

Amount of Net Income (Loss) attributable to noncontrolling interest.

+ References + Details

Operations and Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Cash, Cash Equivalents and Restricted Cash [Abstract]
Cash and Cash Equivalents	$ 32.0	$ 71.9	$ 29.9	$ 36.4
Restricted Cash included in Prepayments and Other	5.9	5.1	7.4	1.5
Restricted Cash included in Other Non-Current Assets	2.4	2.4	2.3	2.3
Cash, Cash Equivalents and Restricted Cash on the Consolidated Statement of Cash Flows	$ 40.3	$ 79.4	$ 39.6	$ 40.2

Regulatory Matters - Electric Rates (Details) - USD ($) $ in Thousands						3 Months Ended
	May 03, 2024	Apr. 01, 2024	Mar. 29, 2024	Dec. 19, 2023	Nov. 01, 2023	Mar. 31, 2024	Sep. 30, 2023	Mar. 31, 2023	Dec. 31, 2023
Regulatory Matters [Line Items]
Regulatory Assets						$ 409,000			$ 425,400
Regulatory Liabilities						564,000			$ 574,000
ECO Annual Filing Member \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Revenue from cost recovery riders and other regulatory programs							$ 2,200
ECO Annual Filing Member \| MPUC \| Minnesota Power \| Subsequent Event
Regulatory Matters [Line Items]
Revenue from cost recovery riders and other regulatory programs		$ 2,200
Electric Rates \| Fuel Adjustment Clause 2023 \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Regulatory Assets						13,000
Retail Customers \| Electric Rates \| Current Cost Recovery Rider \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Revenue from cost recovery riders and other regulatory programs						8,300		$ 16,400
Retail Customers \| Electric Rates \| 2024 Minnesota General Rate Case \| MPUC \| Minnesota Power
Regulatory Matters [Line Items]
Requested rate increase percent					12.00%
Approved rate increase				$ 64,000
Requested return on equity					10.30%
Requested equity capital structure					53.00%
Annual additional revenue generated from requested final rate increase					$ 89,000
Regulatory liabilities						$ 5,500
Retail Customers \| Electric Rates \| 2024 Minnesota General Rate Case \| MPUC \| Minnesota Power \| Subsequent Event
Regulatory Matters [Line Items]
Requested return on equity	9.78%
Annual additional revenue generated from requested final rate increase	$ 33,970
Retail Customers \| Electric Rates \| 2024 Wisconsin General Rate Case \| PSCW \| SWL&P
Regulatory Matters [Line Items]
Requested rate increase percent			5.90%
Requested return on equity			10.00%
Requested equity capital structure			55.00%
Annual additional revenue generated from requested final rate increase			$ 7,300

Business Segments

3 Months Ended

Mar. 31, 2024

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 New Energy, a renewable energy development company, BNI Energy, our coal mining operations in North Dakota, 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 10. BUSINESS SEGMENTS (Continued)


	Three Months Ended
	March 31,
		2024	2023
Millions
Operating Revenue
Regulated Operations
Residential		$51.5	$49.4
Commercial		49.7	47.7
Municipal		9.0	8.9
Industrial		159.5	144.9
Other Power Suppliers		40.0	35.9

Other		28.6	25.8
Total Regulated Operations		338.3	312.6

ALLETE Clean Energy
Long-term PSA		17.8	18.4
Sale of Wind Energy Facilities		—	181.8
Other		1.3	1.3
Total ALLETE Clean Energy		19.1	201.5







Corporate and Other
Long-term Contract		25.4	25.5
Sale of Renewable Development Projects		13.9	19.8
Other		6.6	5.5
Total Corporate and Other		45.9	50.8

Total Operating Revenue		$403.3	$564.9
Net Income Attributable to ALLETE
Regulated Operations		$44.2	$40.6

ALLETE Clean Energy		3.8	8.5



Corporate and Other		2.7	9.1
Total Net Income Attributable to ALLETE		$50.7	$58.2


	March 31, 2024	December 31, 2023
Millions
Assets
Regulated Operations	$4,345.1	$4,335.0

ALLETE Clean Energy	1,580.0	1,594.1

Corporate and Other	679.5	727.3
Total Assets	$6,604.6	$6,656.4

- 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
-SubTopic 10
-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
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-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
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 31
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-31

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-42

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 40
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-40

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//280/tableOfContent

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 26
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-26

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-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
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 41
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-41

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-21

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-21

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

+ Details

Consolidated Statement of Income Unaudited - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating Revenue
Contracts with Customers – Utility	$ 338.3	$ 312.6
Contracts with Customers – Non-utility	63.7	251.0
Other – Non-utility	1.3	1.3
Total Operating Revenue	403.3	564.9
Operating Expenses
Fuel, Purchased Power and Gas – Utility	133.5	118.6
Transmission Services – Utility	22.7	20.1
Cost of Sales – Non-utility	24.4	210.5
Operating and Maintenance	91.7	85.7
Depreciation and Amortization	65.0	62.3
Taxes Other than Income Taxes	18.7	19.4
Total Operating Expenses	356.0	516.6
Operating Income	47.3	48.3
Other Income (Expense)
Interest Expense	(20.4)	(19.3)
Equity Earnings	5.5	6.0
Other	8.6	4.1
Total Other Expense	(6.3)	(9.2)
Income Before Income Taxes	41.0	39.1
Income Tax Expense	4.0	1.5
Net Income	37.0	37.6
Net Loss Attributable to Non-Controlling Interest	(13.7)	(20.6)
Net Income Attributable to ALLETE	$ 50.7	$ 58.2
Earnings Per Share [Abstract]
Basic (in shares)	57.6	57.3
Diluted (in shares)	57.7	57.3
Basic Earnings Per Share of Common Stock (in usd per share)	$ 0.88	$ 1.02
Diluted Earnings Per Share of Common Stock (in usd per share)	$ 0.88	$ 1.02

Regulatory Matters - Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Assets	$ 8.7	$ 9.3
Total Non-Current Regulatory Assets	409.0	425.4
Total Current Regulatory Liabilities	17.1	3.9
Total Non-Current Regulatory Liabilities	564.0	574.0
Fuel Adjustment Clause
Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Liabilities	9.0	0.0
Total Non-Current Regulatory Liabilities	8.2	15.5
Provision for Interim Rate Refund
Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Liabilities	5.5	0.0
Transmission Formula Rates Refund
Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Liabilities	1.0	1.5
Other
Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Liabilities	1.6	2.4
Total Non-Current Regulatory Liabilities	6.1	4.4
Income Taxes
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	302.3	310.0
Wholesale and Retail Contra AFUDC
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	77.3	78.0
Plant Removal Obligations
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	69.3	67.0
Defined Benefit Pension and Other Postretirement Benefit Plans
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	45.5	48.6
Non-Jurisdictional Land Sales
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	35.1	30.2
Investment Tax Credits
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Liabilities	13.5	13.6
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	8.1	8.7
Total Non-Current Regulatory Assets	2.1	5.0
Other
Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Assets	0.6	0.6
Total Non-Current Regulatory Assets	3.3	4.2
Defined Benefit Pension and Other Postretirement Benefit Plans
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	217.3	218.6
Income Taxes
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	85.1	88.1
Asset Retirement Obligations
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	38.3	37.7
Cost Recovery Riders
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	27.6	33.8
Taconite Harbor
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	18.3	20.9
Manufactured Gas Plant
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	13.1	13.2
PPACA Income Tax Deferral
Regulatory Assets and Liabilities [Line Items]
Total Non-Current Regulatory Assets	$ 3.9	$ 3.9

Income Tax Expense - Schedule of Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Current Income Tax Expense
Federal	$ 3.5	$ 5.6
State	3.4	2.2
Total Current Income Tax Expense	6.9	7.8
Deferred Income Tax Expense (Benefit)
Federal	(5.0)	(8.3)
State	2.4	2.1
Investment Tax Credit Amortization	(0.3)	(0.1)
Total Deferred Income Tax Benefit	(2.9)	(6.3)
Total Income Tax Expense	$ 4.0	$ 1.5

Earnings Per Share and Common Stock

3 Months Ended

Mar. 31, 2024

Earnings Per Share [Abstract]

Earnings Per Share and Common Stock

EARNINGS PER SHARE AND COMMON STOCK

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.


Three Months Ended March 31,		2024			2023
Reconciliation of Basic and Diluted		Dilutive			Dilutive
Earnings Per Share	Basic	Securities	Diluted	Basic	Securities	Diluted
Millions Except Per Share Amounts




Net Income Attributable to ALLETE	$50.7		$50.7	$58.2		$58.2
Average Common Shares	57.6	0.1	57.7	57.3	—	57.3
Earnings Per Share	$0.88		$0.88	$1.02		$1.02

Operations and Significant Accounting Policies - Other Non-Current Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Business Segments [Line Items]
Asset Retirement Obligation	$ 206.1	$ 202.9
PSAs	19.5	20.9
Operating Lease Liabilities	8.3	7.7
Finance Lease Liabilities	1.5	1.6
Other	32.6	31.2
Other Non-Current Liabilities	268.0	264.3
BNI Energy
Business Segments [Line Items]
Other Receivables	$ 37.2	$ 37.2

Consolidated Statement of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating Activities
Net Income	$ 37.0	$ 37.6
Adjustments to Reconcile Net Income to Cash provided by (used in) Operating Activities:
AFUDC – Equity	(1.2)	(0.5)
Loss (Income) on Investments and Property, Plant and Equipment	(0.5)	0.4
Depreciation Expense	65.0	62.3
Amortization of PSAs	(1.3)	(1.3)
Amortization of Other Intangible Assets and Other Assets	1.6	1.9
Deferred Income Tax Benefit	(2.9)	(6.3)
Share-Based and ESOP Compensation Expense	1.7	0.8
Defined Benefit Pension and Other Postretirement Plan Benefit	(3.4)	(0.8)
Fuel Adjustment Clause	4.9	15.3
Bad Debt Expense	0.3	0.3
Provision for Interim Rate Refund	5.5	5.1
Changes in Operating Assets and Liabilities
Accounts Receivable	(5.5)	17.3
Inventories	(7.3)	109.0
Prepayments and Other	6.7	11.0
Accounts Payable	(10.4)	(10.7)
Other Current Liabilities	(19.8)	(142.2)
Cash Contributions to Defined Benefit Pension Plans	(25.0)	(6.5)
Changes in Regulatory and Other Non-Current Assets	9.1	(0.7)
Changes in Regulatory and Other Non-Current Liabilities	5.6	0.4
Cash provided by Operating Activities	60.1	92.4
Investing Activities
Proceeds from Sale of Available-for-sale Securities	1.4	0.0
Payments for Purchase of Available-for-sale Securities	(1.5)	0.0
Payments for Equity Method Investments	(1.6)	(0.8)
Additions to Property, Plant and Equipment	(60.6)	(70.0)
Other Investing Activities	1.5	(3.9)
Cash used in Investing Activities	(60.8)	(74.7)
Financing Activities
Proceeds from Issuance of Common Stock	2.0	3.3
Proceeds from Issuance of Short-Term and Long-Term Debt	156.0	238.5
Repayments of Short-Term and Long-Term Debt	(158.0)	(227.8)
Proceeds from Non-Controlling Interest in Subsidiaries – Net	2.7	6.7
Distributions to Non-Controlling Interest	(0.5)	(0.3)
Dividends on Common Stock	(40.6)	(38.8)
Other Financing Activities	0.0	0.1
Cash used in Financing Activities	(38.4)	(18.3)
Change in Cash, Cash Equivalents and Restricted Cash	(39.1)	(0.6)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	79.4	40.2
Cash, Cash Equivalents and Restricted Cash at End of Period	$ 40.3	$ 39.6

Short-Term and Long-Term Debt - Narrative (Details) $ in Millions	Apr. 23, 2024 USD ($)	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Debt Instrument [Line Items]
Actual ratio of indebtedness to total capitalization		0.36
ALLETE Bonds 4.98% Due April 2033 \| Subsequent Event
Debt Instrument [Line Items]
Proceeds from issuance of first mortgage bond	$ 100.0
Interest rate	5.72%
Credit Agreement \| Line of Credit
Debt Instrument [Line Items]
Letters of credit outstanding		$ 19.4	$ 19.4
Line of credit draw outstanding		$ 94.0	$ 34.1
Minimum
Debt Instrument [Line Items]
Required ratio of indebtedness to total capitalization		0.65
Maximum
Debt Instrument [Line Items]
Required ratio of indebtedness to total capitalization		1.00

Operations and Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Subsequent Events	Subsequent Events. The Company performed an evaluation of subsequent events for potential recognition and disclosure through the date of the financial statements issuance.
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 March 31, 2024, restricted cash amounts included in Prepayments and Other on the Consolidated Balance Sheet include collateral deposits required under an ALLETE Clean Energy loan. The restricted cash amounts included in Other Non-Current Assets represent collateral deposits required under an ALLETE Clean Energy loan agreement as well as PSAs.
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.
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. 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.
Investment in ATC	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.
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.Non-financial assets such as equity method investments, land inventory, 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.
Power Purchase and Sale Agreements	Power Purchase and Sale 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.
Environmental Matters	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.
Earnings Per Share and Common Stock	EARNINGS PER SHARE AND COMMON STOCKWe 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.
Income Tax Expense	The Company's tax provision for interim periods is determined using an estimate of its annual effective tax rate, adjusted for discrete items arising in that quarter. In each quarter, the Company updates its estimate of the annual effective tax rate and if the estimated annual effective tax rate changes, the Company would make a cumulative adjustment in that quarter.
Uncertain Tax Positions	The unrecognized tax benefit amounts have been presented as an increase to the net deferred tax liability on the Consolidated Balance Sheet.
Business Segments	BUSINESS SEGMENTSWe 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.
New Accounting Pronouncements and Disclosure Rules.	New Accounting Pronouncements and Disclosure Rules. SEC Climate-related Disclosures Rule. On March 6, 2024, the SEC issued the final rules regarding the enhancement and standardization of climate-related disclosures for investors (Rule). The Rule requires registrants to provide certain climate-related information in their annual reports and registration statements. These requirements include disclosing climate-related risks that materially affect or are reasonably likely to materially affect a registrant’s business strategy, results of operations, or financial condition as well as certain disclosures related to greenhouse-gas emissions, and the effects of severe weather events and other natural conditions. The disclosure requirements will begin phasing in for annual periods beginning in 2025. The Company is evaluating the final rule to determine its impact on the Company’s disclosures. The Rule is currently being challenged before the U.S. Court of Appeals, and the SEC issued a voluntary stay of the Rule on April 4, 2024, pending judicial review. There are no other new accounting pronouncements or rules that we anticipate having a material effect on the presentation of ALLETE’s consolidated financial statements.

Pension and Other Postretirement Benefit Plans (Tables)

3 Months Ended

Mar. 31, 2024

Retirement Benefits [Abstract]

Components of Net Periodic Benefit Cost (Credit)


Components of Net Periodic Benefit Cost (Credit)	Pension		Other Postretirement
Three Months Ended March 31,	2024	2023	2024	2023
Millions










Service Cost	$1.6	$1.6	$0.4	$0.6
Non-Service Cost Components (a)
Interest Cost	9.7	10.1	1.0	1.5
Expected Return on Plan Assets	(11.2)	(10.9)	(2.8)	(2.8)
Amortization of Prior Service Credits	—	—	(2.9)	(1.8)
Amortization of Net Loss	1.6	1.4	(0.8)	(0.5)

Net Periodic Benefit Cost (Credit)	$1.7	$2.2	$(5.1)	$(3.0)

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

Pay vs Performance Disclosure - USD ($) $ in Millions	3 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Millions	Mar. 31, 2024	Mar. 31, 2023
Pay vs Performance Disclosure
Net Income Attributable to ALLETE	$ 50.7	$ 58.2

- Definition

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

+ References

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+ Details

Operations and Significant Accounting Policies

3 Months Ended

Mar. 31, 2024

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Operations and Significant Accounting Policies

OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES

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

On May 5, 2024, ALLETE entered into the Merger Agreement. (See Note 11. Subsequent Event – Agreement and Plan of Merger.)

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 March 31, 2024, restricted cash amounts included in Prepayments and Other on the Consolidated Balance Sheet include collateral deposits required under an ALLETE Clean Energy loan. The restricted cash amounts included in Other Non-Current Assets represent collateral deposits required under an ALLETE Clean Energy loan agreement as well as 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	March 31, 2024	December 31, 2023	March 31, 2023	December 31, 2022
Millions
Cash and Cash Equivalents	$32.0	$71.9	$29.9	$36.4
Restricted Cash included in Prepayments and Other	5.9	5.1	7.4	1.5
Restricted Cash included in Other Non-Current Assets	2.4	2.4	2.3	2.3
Cash, Cash Equivalents and Restricted Cash on the Consolidated Statement of Cash Flows	$40.3	$79.4	$39.6	$40.2

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	March 31, 2024	December 31, 2023
Millions
Fuel (a)	$30.2	$27.2
Materials and Supplies	119.0	115.7
Renewable Energy Facilities Under Development (b)	33.5	32.5



Total Inventories – Net	$182.7	$175.4

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

(b) Renewable Energy Facilities Under Development as of March 31, 2024, consists primarily of project costs related to renewable energy development projects at New Energy.

Goodwill. The aggregate carrying amount of goodwill was $154.9 million as of March 31, 2024 ($154.9 million as of December 31, 2023). There have been no changes to goodwill by reportable segment for the quarter and three months ended March 31, 2024.

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)


Other Non-Current Assets	March 31, 2024	December 31, 2023
Millions
Other Postretirement Benefit Plans	$104.6	$106.3
Contract Assets (a)	17.9	18.5

Operating Lease Right-of-use Assets	11.3	10.7
ALLETE Properties	10.7	10.8
Restricted Cash	2.4	2.4
Finance Lease Right-of-use Assets	2.0	2.1
Other	115.9	112.1
Total Other Non-Current Assets	$264.8	$262.9

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


Other Current Liabilities	March 31, 2024	December 31, 2023
Millions

PSAs	$6.0	$6.0
Customer Deposits	5.7	7.4

Provision for Interim Rate Refund	5.5	—


Operating Lease Liabilities	3.1	3.0

Finance Lease Liabilities	0.4	0.4
Other	59.5	75.1
Total Other Current Liabilities	$80.2	$91.9


Other Non-Current Liabilities	March 31, 2024	December 31, 2023
Millions
Asset Retirement Obligation (a)	$206.1	$202.9
PSAs	19.5	20.9


Operating Lease Liabilities	8.3	7.7
Finance Lease Liabilities	1.5	1.6
Other	32.6	31.2
Total Other Non-Current Liabilities	$268.0	$264.3

(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 March 31, 2024 ($37.2 million as of December 31, 2023).

NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)


	Three Months Ended
	March 31,
Other Income		2024	2023
Millions
Pension and Other Postretirement Benefit Plan Non-Service Credits (a)		$4.3	$2.0
Interest and Investment Income		1.9	1.1
AFUDC - Equity		1.2	0.5


Other		1.2	0.5
Total Other Income		$8.6	$4.1

(a)These are components of net periodic pension and other postretirement benefit cost other than service cost. (See Note 9. Pension and Other Postretirement Benefit Plans.)


	Three Months Ended
	March 31,
Supplemental Statement of Cash Flows Information	2024	2023
Millions
Cash Paid for Interest – Net of Amounts Capitalized	$25.7	$24.6

Noncash Investing and Financing Activities

Decrease in Accounts Payable for Capital Additions to Property, Plant and Equipment	$(5.9)	$(7.1)

Capitalized Asset Retirement Costs	$2.2	$2.4
AFUDC–Equity	$1.2	$0.5

New Accounting Pronouncements and Disclosure Rules.

SEC Climate-related Disclosures Rule. On March 6, 2024, the SEC issued the final rules regarding the enhancement and standardization of climate-related disclosures for investors (Rule). The Rule requires registrants to provide certain climate-related information in their annual reports and registration statements. These requirements include disclosing climate-related risks that materially affect or are reasonably likely to materially affect a registrant’s business strategy, results of operations, or financial condition as well as certain disclosures related to greenhouse-gas emissions, and the effects of severe weather events and other natural conditions. The disclosure requirements will begin phasing in for annual periods beginning in 2025. The Company is evaluating the final rule to determine its impact on the Company’s disclosures. The Rule is currently being challenged before the U.S. Court of Appeals, and the SEC issued a voluntary stay of the Rule on April 4, 2024, pending judicial review.

There are no other new accounting pronouncements or rules that we anticipate having a material effect on the presentation of ALLETE’s consolidated financial statements.

Income Tax Expense

3 Months Ended

Mar. 31, 2024

Income Tax Disclosure [Abstract]

Income Tax Expense

INCOME TAX EXPENSE


	Three Months Ended
	March 31,
		2024	2023
Millions
Current Income Tax Expense
Federal (a)		$3.5	$5.6
State		3.4	2.2
Total Current Income Tax Expense		$6.9	$7.8
Deferred Income Tax Expense (Benefit)
Federal (b)		$(5.0)	$(8.3)
State		2.4	2.1
Investment Tax Credit Amortization		(0.3)	(0.1)
Total Deferred Income Tax Benefit		$(2.9)	$(6.3)
Total Income Tax Expense		$4.0	$1.5

(a)For the three months ended March 31, 2024 and 2023, the federal current tax expense was partially offset by production tax credits.

(b)For the three months ended March 31, 2024 and 2023, the federal income tax benefit is primarily due to production tax credits.

The Company's tax provision for interim periods is determined using an estimate of its annual effective tax rate, adjusted for discrete items arising in that quarter. In each quarter, the Company updates its estimate of the annual effective tax rate and if the estimated annual effective tax rate changes, the Company would make a cumulative adjustment in that quarter.


	Three Months Ended
Reconciliation of Taxes from Federal Statutory	March 31,
Rate to Total Income Tax Expense		2024		2023
Millions
Income Before Income Taxes		$41.0		$39.1


Statutory Federal Income Tax Rate		21	%	21	%
Income Taxes Computed at Statutory Federal Rate		$8.6		$8.2
Increase (Decrease) in Income Tax Due to:
State Income Taxes – Net of Federal Income Tax Benefit		4.6		3.4


Production Tax Credits (a)		(11.6)		(10.4)
Investment Tax Credits (a)		(0.3)		(2.2)
Regulatory Differences – Excess Deferred Tax		(3.5)		(2.8)
Non-Controlling Interest in Subsidiaries		2.8		3.8
AFUDC – Equity		(0.6)		(0.3)
Other		4.0		1.8
Total Income Tax Expense		$4.0		$1.5

(a)For the three months ended March 31, 2024 and 2023, the credits are presented net of any estimated discount on the sale of certain credits.

For the three months ended March 31, 2024, the effective tax rate was 9.7 percent (3.8 percent for the three months ended March 31, 2023). The effective tax rates for 2024 and 2023 were primarily impacted by production tax credits.

Uncertain Tax Positions. As of March 31, 2024, we had gross unrecognized tax benefits of $1.1 million ($1.1 million as of December 31, 2023). Of the total gross unrecognized tax benefits, $0.6 million represents the amount of unrecognized tax benefits included on the Consolidated Balance Sheet that, if recognized, would favorably impact the effective income tax rate. The unrecognized tax benefit amounts have been presented as an increase to the net deferred tax liability on the Consolidated Balance Sheet.

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 2021 or state examination for years before 2020. 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

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+ Details

Operations and Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2024

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	March 31, 2024	December 31, 2023	March 31, 2023	December 31, 2022
Millions
Cash and Cash Equivalents	$32.0	$71.9	$29.9	$36.4
Restricted Cash included in Prepayments and Other	5.9	5.1	7.4	1.5
Restricted Cash included in Other Non-Current Assets	2.4	2.4	2.3	2.3
Cash, Cash Equivalents and Restricted Cash on the Consolidated Statement of Cash Flows	$40.3	$79.4	$39.6	$40.2

Inventories – Net

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	March 31, 2024	December 31, 2023
Millions
Fuel (a)	$30.2	$27.2
Materials and Supplies	119.0	115.7
Renewable Energy Facilities Under Development (b)	33.5	32.5



Total Inventories – Net	$182.7	$175.4

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

(b) Renewable Energy Facilities Under Development as of March 31, 2024, consists primarily of project costs related to renewable energy development projects at New Energy.

Other Non-Current Assets


Other Non-Current Assets	March 31, 2024	December 31, 2023
Millions
Other Postretirement Benefit Plans	$104.6	$106.3
Contract Assets (a)	17.9	18.5

Operating Lease Right-of-use Assets	11.3	10.7
ALLETE Properties	10.7	10.8
Restricted Cash	2.4	2.4
Finance Lease Right-of-use Assets	2.0	2.1
Other	115.9	112.1
Total Other Non-Current Assets	$264.8	$262.9

Other Current Liabilities


Other Current Liabilities	March 31, 2024	December 31, 2023
Millions

PSAs	$6.0	$6.0
Customer Deposits	5.7	7.4

Provision for Interim Rate Refund	5.5	—


Operating Lease Liabilities	3.1	3.0

Finance Lease Liabilities	0.4	0.4
Other	59.5	75.1
Total Other Current Liabilities	$80.2	$91.9

Other Non-Current Liabilities


Other Non-Current Liabilities	March 31, 2024	December 31, 2023
Millions
Asset Retirement Obligation (a)	$206.1	$202.9
PSAs	19.5	20.9


Operating Lease Liabilities	8.3	7.7
Finance Lease Liabilities	1.5	1.6
Other	32.6	31.2
Total Other Non-Current Liabilities	$268.0	$264.3

Other Income


	Three Months Ended
	March 31,
Other Income		2024	2023
Millions
Pension and Other Postretirement Benefit Plan Non-Service Credits (a)		$4.3	$2.0
Interest and Investment Income		1.9	1.1
AFUDC - Equity		1.2	0.5


Other		1.2	0.5
Total Other Income		$8.6	$4.1

(a)These are components of net periodic pension and other postretirement benefit cost other than service cost. (See Note 9. Pension and Other Postretirement Benefit Plans.)

Supplemental Statement of Cash Flows Information


	Three Months Ended
	March 31,
Supplemental Statement of Cash Flows Information	2024	2023
Millions
Cash Paid for Interest – Net of Amounts Capitalized	$25.7	$24.6

Noncash Investing and Financing Activities

Decrease in Accounts Payable for Capital Additions to Property, Plant and Equipment	$(5.9)	$(7.1)

Capitalized Asset Retirement Costs	$2.2	$2.4
AFUDC–Equity	$1.2	$0.5

Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pension
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service Cost	$ 1.6	$ 1.6
Interest Cost	9.7	10.1
Expected Return on Plan Assets	(11.2)	(10.9)
Amortization of Prior Service Credits	0.0	0.0
Amortization of Net Loss	1.6	1.4
Net Periodic Benefit Cost (Credit)	1.7	2.2
Other Postretirement
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service Cost	0.4	0.6
Interest Cost	1.0	1.5
Expected Return on Plan Assets	(2.8)	(2.8)
Amortization of Prior Service Credits	(2.9)	(1.8)
Amortization of Net Loss	(0.8)	(0.5)
Net Periodic Benefit Cost (Credit)	$ (5.1)	$ (3.0)

Fair Value

3 Months Ended

Mar. 31, 2024

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). Descriptions of the three levels of the fair value hierarchy are discussed in Note 7. Fair Value to the Consolidated Financial Statements in our 2023 Form 10-K.

NOTE 4. 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 March 31, 2024, and December 31, 2023. 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 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 March 31, 2024
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets
Investments (a)
Available-for-sale – Equity Securities	$8.6	—	—	$8.6
Available-for-sale – Corporate and Governmental Debt Securities (b)	—	$6.5	—	6.5
Cash Equivalents	6.0	—	—	6.0
Total Fair Value of Assets	$14.6	$6.5	—	$21.1

Liabilities
Deferred Compensation (c)	—	$18.1	—	$18.1


Total Fair Value of Liabilities	—	$18.1	—	$18.1



	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	—	$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 March 31, 2024, the aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year or less was $1.7 million, in one year to less than three years was $2.7 million, in three years to less than five years was $1.6 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 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 of the item listed in the following table was based on quoted market prices for the same or similar instruments (Level 2).


Financial Instruments	Carrying Amount	Fair Value
Millions
Short-Term and Long-Term Debt (a)
March 31, 2024	$1,797.3	$1,646.8
December 31, 2023	$1,799.4	$1,670.6

(a)Excludes unamortized debt issuance costs.

NOTE 4. FAIR VALUE (Continued)

Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis. Non-financial assets such as equity method investments, land inventory, 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. For the three months ended March 31, 2024, and the year ended December 31, 2023, there were no indicators of impairment for these non-financial assets.

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 or for facilities without long-term contracts for their entire output. A continued decline or volatility in energy prices or lower wind resource expectations could result in a future impairment.

- 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

Fair Value - Recurring Fair Value Measures (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Liabilities
Aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year	$ 1.7
Aggregate amount of available-for-sale corporate and governmental debt securities maturing after one year through three years	2.7
Aggregate amount of available-for-sale corporate and governmental debt securities maturing after one year through three years after three years through five years	1.6
Aggregate amount of available-for-sale corporate and governmental debt securities maturing after one year through three years after three years through five years after five years	0.5
Recurring Fair Value Measures
Investments [Abstract]
Available-for-sale – Equity Securities	8.6	$ 8.7
Available-for-sale – Corporate and Governmental Debt Securities	6.5	6.0
Cash Equivalents	6.0	5.8
Total Fair Value of Assets	21.1	20.5
Liabilities
Deferred compensation	18.1	16.5
Total Fair Value of Liabilities	18.1	16.5
Recurring Fair Value Measures \| Level 1
Investments [Abstract]
Available-for-sale – Equity Securities	8.6	8.7
Available-for-sale – Corporate and Governmental Debt Securities	0.0	0.0
Cash Equivalents	6.0	5.8
Total Fair Value of Assets	14.6	14.5
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	6.5	6.0
Cash Equivalents	0.0	0.0
Total Fair Value of Assets	6.5	6.0
Liabilities
Deferred compensation	18.1	16.5
Total Fair Value of Liabilities	18.1	16.5
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

Pension and Other Postretirement Benefit Plans - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pension
Pension and Other Postretirement Benefit Plans [Line Items]
Employer contributions	$ 25.0	$ 6.5
Expected future employer contributions	0.0
Other Postretirement
Pension and Other Postretirement Benefit Plans [Line Items]
Employer contributions	0.0	$ 0.0
Expected future employer contributions	$ 0.0

Operations and Significant Accounting Policies - Other Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Other Income
Total Other Income	$ 8.6	$ 4.1
Pension and Other Postretirement Benefit Plan Non-Service Credits
Other Income
Total Other Income	4.3	2.0
Interest and Investment Income
Other Income
Total Other Income	1.9	1.1
AFUDC - Equity
Other Income
Total Other Income	1.2	0.5
Other
Other Income
Total Other Income	$ 1.2	$ 0.5

Short-Term and Long-Term Debt - Schedule of Short-Term and Long-Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Principal
Short-Term Debt	$ 17.2	$ 111.5
Long-Term Debt	1,780.1	1,687.9
Total Debt	1,797.3	1,799.4
Unamortized Debt Issuance Costs
Short-Term Debt	0.0	(0.1)
Long-Term Debt	(7.7)	(8.0)
Total Debt	(7.7)	(8.1)
Total
Short-Term Debt	17.2	111.4
Long-Term Debt	1,772.4	1,679.9
Total Debt	$ 1,789.6	$ 1,791.3

Income Tax Expense (Tables)

3 Months Ended

Mar. 31, 2024

Income Tax Disclosure [Abstract]

Income Tax Expense


	Three Months Ended
	March 31,
		2024	2023
Millions
Current Income Tax Expense
Federal (a)		$3.5	$5.6
State		3.4	2.2
Total Current Income Tax Expense		$6.9	$7.8
Deferred Income Tax Expense (Benefit)
Federal (b)		$(5.0)	$(8.3)
State		2.4	2.1
Investment Tax Credit Amortization		(0.3)	(0.1)
Total Deferred Income Tax Benefit		$(2.9)	$(6.3)
Total Income Tax Expense		$4.0	$1.5

(a)For the three months ended March 31, 2024 and 2023, the federal current tax expense was partially offset by production tax credits.

(b)For the three months ended March 31, 2024 and 2023, the federal income tax benefit is primarily due to production tax credits.

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

In each quarter, the Company updates its estimate of the annual effective tax rate and if the estimated annual effective tax rate changes, the Company would make a cumulative adjustment in that quarter.


	Three Months Ended
Reconciliation of Taxes from Federal Statutory	March 31,
Rate to Total Income Tax Expense		2024		2023
Millions
Income Before Income Taxes		$41.0		$39.1


Statutory Federal Income Tax Rate		21	%	21	%
Income Taxes Computed at Statutory Federal Rate		$8.6		$8.2
Increase (Decrease) in Income Tax Due to:
State Income Taxes – Net of Federal Income Tax Benefit		4.6		3.4


Production Tax Credits (a)		(11.6)		(10.4)
Investment Tax Credits (a)		(0.3)		(2.2)
Regulatory Differences – Excess Deferred Tax		(3.5)		(2.8)
Non-Controlling Interest in Subsidiaries		2.8		3.8
AFUDC – Equity		(0.6)		(0.3)
Other		4.0		1.8
Total Income Tax Expense		$4.0		$1.5

(a)For the three months ended March 31, 2024 and 2023, the credits are presented net of any estimated discount on the sale of certain credits.

Regulatory Matters (Tables)

3 Months Ended

Mar. 31, 2024

Regulated Operations [Abstract]

Regulatory Assets and Liabilities

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.


Regulatory Assets and Liabilities	March 31, 2024	December 31, 2023
Millions
Current Regulatory Assets (a)
Fuel Adjustment Clause	$8.1	$8.7
Other	0.6	0.6
Total Current Regulatory Assets	$8.7	$9.3
Non-Current Regulatory Assets
Defined Benefit Pension and Other Postretirement Plans	$217.3	$218.6
Income Taxes	85.1	88.1
Asset Retirement Obligations	38.3	37.7
Cost Recovery Riders	27.6	33.8
Taconite Harbor	18.3	20.9
Manufactured Gas Plant	13.1	13.2
PPACA Income Tax Deferral	3.9	3.9
Fuel Adjustment Clause	2.1	5.0


Other	3.3	4.2
Total Non-Current Regulatory Assets	$409.0	$425.4


Current Regulatory Liabilities (b)
Fuel Adjustment Clause	$9.0	—
Provision for Interim Rate Refund	5.5	—
Transmission Formula Rates Refund	1.0	$1.5
Other	1.6	2.4
Total Current Regulatory Liabilities	$17.1	$3.9
Non-Current Regulatory Liabilities
Income Taxes	$302.3	$310.0
Wholesale and Retail Contra AFUDC	77.3	78.0
Plant Removal Obligations	69.3	67.0
Defined Benefit Pension and Other Postretirement Benefit Plans	45.5	48.6
Non-Jurisdictional Land Sales	35.1	30.2
Investment Tax Credits	13.5	13.6
Fuel Adjustment Clause	8.2	15.5


Boswell Units 1 and 2 Net Plant and Equipment	6.7	6.7
Other	6.1	4.4
Total Non-Current Regulatory Liabilities	$564.0	$574.0

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

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

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Mar. 31, 2024
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

Short-Term and Long-Term Debt

3 Months Ended

Mar. 31, 2024

Debt Disclosure [Abstract]

Short-Term and Long-Term Debt

SHORT-TERM AND LONG-TERM DEBT

The following tables present the Company’s short-term and long-term debt as of March 31, 2024, and December 31, 2023:


March 31, 2024	Principal	Unamortized Debt Issuance Costs	Total
Millions
Short-Term Debt	$17.2	—	$17.2
Long-Term Debt	1,780.1	$(7.7)	1,772.4
Total Debt	$1,797.3	$(7.7)	$1,789.6


December 31, 2023	Principal	Unamortized Debt Issuance Costs	Total
Millions
Short-Term Debt	$111.5	$(0.1)	$111.4
Long-Term Debt	1,687.9	(8.0)	1,679.9
Total Debt	$1,799.4	$(8.1)	$1,791.3

We had $19.4 million outstanding in standby letters of credit and $94.0 million outstanding draws under our lines of credit as of March 31, 2024 ($19.4 million in standby letters of credit and $34.1 million outstanding draws as of December 31, 2023). We also have standby letters of credit outstanding under other letter of credit facilities. (See Note 6. Commitments, Guarantees and Contingencies.)

On April 23, 2024, ALLETE issued $100 million of its First Mortgage Bonds (Bonds) to certain institutional buyers in the private placement market. The Bonds, which bear interest at 5.72 percent, will mature in April 2039 and pay interest semi-annually in April and October of each year, commencing on October 30, 2024. 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.

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 March 31, 2024, 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 March 31, 2024, 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
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-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
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-Name Accounting Standards Codification
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-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
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
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-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

Equity Investments - Narrative (Details) $ in Millions	3 Months Ended
Equity Investments - Narrative (Details) $ in Millions	Mar. 31, 2024 USD ($) MW
Wind Turbine Generators \| Tenaska \| Tenaska PPA \| Minnesota Power
Investments In ATC [Roll Forward]
Generating capacity counterparty owned (MegaWatt) \| MW	250
Long-term contract for purchase of electric power	20 years
ATC
Investments In ATC [Roll Forward]
Ownership percentage	8.00%
Authorized return on equity	10.02%
Authorized return on equity, including incentive adder	10.52%
Basis point incentive adder	0.50%
Approximate annual reduction in pretax income for FERC proposal to limit incentive adder, Allete's proportionate share \| $	$ 1
Nobles 2
Investments In ATC [Roll Forward]
Ownership percentage	49.00%

Operations and Significant Accounting Policies - Inventories (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Fuel	$ 30.2	$ 27.2
Materials and Supplies	119.0	115.7
Renewable Energy Facilities Under Development	33.5	32.5
Inventories – Net	$ 182.7	$ 175.4

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, 2022		$ 1,781.5	$ (24.4)	$ 934.8	$ 656.4
Consolidated Statement of Equity [Roll Forward]
Common Stock Issued		4.1
Unrealized Gain on Debt Securities	$ 0.1		0.1
Defined Benefit Pension and Other Postretirement Plans	0.0		0.0
Net Income Attributable to ALLETE	58.2			58.2
Common Stock Dividends				(38.8)
Proceeds from Non-Controlling Interest in Subsidiaries – Net					6.7
Net Loss Attributable to Non-Controlling Interest	20.6				(20.6)
Distributions to Non-Controlling Interest					(0.3)
Balance, End of Period at Mar. 31, 2023	3,357.7	1,785.6	(24.3)	954.2	642.2
Balance, Beginning of Period at Dec. 31, 2022	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 Mar. 31, 2023	$ 0.0
Redeemable Non-Controlling Interest
Dividends Per Share of Common Stock (in usd per share	$ 0.6775
Balance, Beginning of Period at Dec. 31, 2023	$ 3,406.6	1,803.7	(20.5)	1,026.4	597.0
Consolidated Statement of Equity [Roll Forward]
Common Stock Issued		3.7
Unrealized Gain on Debt Securities	0.0		0.0
Defined Benefit Pension and Other Postretirement Plans	(0.4)		(0.4)
Net Income Attributable to ALLETE	50.7			50.7
Common Stock Dividends				(40.6)
Proceeds from Non-Controlling Interest in Subsidiaries – Net					0.0
Net Loss Attributable to Non-Controlling Interest	13.7				(11.0)
Distributions to Non-Controlling Interest					(0.5)
Balance, End of Period at Mar. 31, 2024	3,408.5	$ 1,807.4	$ (20.9)	$ 1,036.5	$ 585.5
Balance, Beginning of Period at Dec. 31, 2023	0.5
Redeemable Non-Controlling Interest
Proceeds from Non-Controlling Interest in Subsidiaries	2.7
Net Loss Attributable to Non-Controlling Interest	(2.7)
Total Redeemable Non-Controlling Interest at Mar. 31, 2024	$ 0.5
Redeemable Non-Controlling Interest
Dividends Per Share of Common Stock (in usd per share	$ 0.705

Equity Investments

3 Months Ended

Mar. 31, 2024

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.


ALLETE’s Investment in ATC
Millions
Equity Investment Balance as of December 31, 2023			$179.7
Cash Investments			1.6
Equity in ATC Earnings			5.7
Distributed ATC Earnings			(4.6)
Amortization of the Remeasurement of Deferred Income Taxes			0.3
Equity Investment Balance as of March 31, 2024			$182.7

ATC’s authorized return on equity was 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. We cannot predict the return on equity the FERC will ultimately authorize in the remanded proceeding.

In addition, the FERC issued a Notice of Proposed Rulemaking in 2021 proposing to limit the 0.50 percent 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.

Investment in Nobles 2. Our subsidiary, ALLETE South Wind, owns 49 percent of 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, 2023			$151.5

Equity in Nobles 2 Earnings (a)			(0.2)
Distributed Nobles 2 Earnings			(0.9)
Equity Investment Balance as of March 31, 2024			$150.4

(a)The Company also recorded earnings from net loss attributable to non-controlling interest of $3.0 million related to its investment in Nobles 2.

Consolidated Statement of Comprehensive Income Unaudited Parentheticals - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Unrealized gain on securities, income tax expense	$ 0.0	$ 0.1
Defined benefit pension and other postretirement benefit plans, income tax expense	$ 0.1	$ 0.0

Fair Value (Tables)

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Abstract]

Recurring Fair Value Measures

The estimated fair value of Cash and Cash Equivalents 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 March 31, 2024
Recurring Fair Value Measures	Level 1	Level 2	Level 3	Total
Millions
Assets
Investments (a)
Available-for-sale – Equity Securities	$8.6	—	—	$8.6
Available-for-sale – Corporate and Governmental Debt Securities (b)	—	$6.5	—	6.5
Cash Equivalents	6.0	—	—	6.0
Total Fair Value of Assets	$14.6	$6.5	—	$21.1

Liabilities
Deferred Compensation (c)	—	$18.1	—	$18.1


Total Fair Value of Liabilities	—	$18.1	—	$18.1



	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	—	$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 of Financial Instruments

The fair value of the item listed in the following table was based on quoted market prices for the same or similar instruments (Level 2).


Financial Instruments	Carrying Amount	Fair Value
Millions
Short-Term and Long-Term Debt (a)
March 31, 2024	$1,797.3	$1,646.8
December 31, 2023	$1,799.4	$1,670.6

(a)Excludes unamortized debt issuance costs.

Short-Term and Long-Term Debt (Tables)

3 Months Ended

Mar. 31, 2024

Debt Disclosure [Abstract]

Schedule of Short-Term and Long-Term Debt

The following tables present the Company’s short-term and long-term debt as of March 31, 2024, and December 31, 2023:


March 31, 2024	Principal	Unamortized Debt Issuance Costs	Total
Millions
Short-Term Debt	$17.2	—	$17.2
Long-Term Debt	1,780.1	$(7.7)	1,772.4
Total Debt	$1,797.3	$(7.7)	$1,789.6


December 31, 2023	Principal	Unamortized Debt Issuance Costs	Total
Millions
Short-Term Debt	$111.5	$(0.1)	$111.4
Long-Term Debt	1,687.9	(8.0)	1,679.9
Total Debt	$1,799.4	$(8.1)	$1,791.3

Operations and Significant Accounting Policies - Other Current Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
PSAs	$ 6.0	$ 6.0
Customer Deposits	5.7	7.4
Provision for Interim Rate Refund	5.5	0.0
Operating Lease Liabilities	3.1	3.0
Finance Lease Liabilities	0.4	0.4
Other	59.5	75.1
Total Other Current Liabilities	$ 80.2	$ 91.9

Operations and Significant Accounting Policies - Supplemental Statement of Cash Flows Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash Paid for Interest – Net of Amounts Capitalized	$ 25.7	$ 24.6
Noncash Investing and Financing Activities
Decrease in Accounts Payable for Capital Additions to Property, Plant and Equipment	(5.9)	(7.1)
Capitalized Asset Retirement Costs	2.2	2.4
AFUDC–Equity	$ 1.2	$ 0.5

Consolidated Statement of Comprehensive Income Unaudited - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Comprehensive Income [Abstract]
Net Income	$ 37.0	$ 37.6
Other Comprehensive Income (Loss)
Net of Income Tax Expense of $– and $0.1	0.0	0.1
Net of Income Tax Expense of $0.1 and $–	(0.4)	0.0
Total Other Comprehensive Income (Loss)	(0.4)	0.1
Total Comprehensive Income	36.6	37.7
Net Loss Attributable to Non-Controlling Interest	(13.7)	(20.6)
Total Comprehensive Income Attributable to ALLETE	$ 50.3	$ 58.3

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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.

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

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-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481203/810-10-50-1A

Reference 39: http://www.xbrl.org/2003/role/disclosureRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481203/810-10-50-1A

+ Details

Business Segments (Tables)

3 Months Ended

Mar. 31, 2024

Segment Reporting [Abstract]

Business Segments

We also present Corporate and Other which includes New Energy, a renewable energy development company, BNI Energy, our coal mining operations in North Dakota, 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 10. BUSINESS SEGMENTS (Continued)


	Three Months Ended
	March 31,
		2024	2023
Millions
Operating Revenue
Regulated Operations
Residential		$51.5	$49.4
Commercial		49.7	47.7
Municipal		9.0	8.9
Industrial		159.5	144.9
Other Power Suppliers		40.0	35.9

Other		28.6	25.8
Total Regulated Operations		338.3	312.6

ALLETE Clean Energy
Long-term PSA		17.8	18.4
Sale of Wind Energy Facilities		—	181.8
Other		1.3	1.3
Total ALLETE Clean Energy		19.1	201.5







Corporate and Other
Long-term Contract		25.4	25.5
Sale of Renewable Development Projects		13.9	19.8
Other		6.6	5.5
Total Corporate and Other		45.9	50.8

Total Operating Revenue		$403.3	$564.9
Net Income Attributable to ALLETE
Regulated Operations		$44.2	$40.6

ALLETE Clean Energy		3.8	8.5



Corporate and Other		2.7	9.1
Total Net Income Attributable to ALLETE		$50.7	$58.2


	March 31, 2024	December 31, 2023
Millions
Assets
Regulated Operations	$4,345.1	$4,335.0

ALLETE Clean Energy	1,580.0	1,594.1

Corporate and Other	679.5	727.3
Total Assets	$6,604.6	$6,656.4

Pension and Other Postretirement Benefit Plans

3 Months Ended

Mar. 31, 2024

Retirement Benefits [Abstract]

Pension and Other Postretirement Benefit Plans

PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS


Components of Net Periodic Benefit Cost (Credit)	Pension		Other Postretirement
Three Months Ended March 31,	2024	2023	2024	2023
Millions










Service Cost	$1.6	$1.6	$0.4	$0.6
Non-Service Cost Components (a)
Interest Cost	9.7	10.1	1.0	1.5
Expected Return on Plan Assets	(11.2)	(10.9)	(2.8)	(2.8)
Amortization of Prior Service Credits	—	—	(2.9)	(1.8)
Amortization of Net Loss	1.6	1.4	(0.8)	(0.5)

Net Periodic Benefit Cost (Credit)	$1.7	$2.2	$(5.1)	$(3.0)

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

Employer Contributions. For the three months ended March 31, 2024, we contributed $25.0 million in cash to the defined benefit pension plans ($6.5 million for the three months ended March 31, 2023); we do not expect to make additional contributions to our defined benefit pension plans in 2024. For the three months ended March 31, 2024 and 2023, we made no contributions to our other postretirement benefit plans; we do not expect to make any contributions to our other postretirement benefit plans in 2024.

- 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
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-Paragraph 17
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-URI https://asc.fasb.org//1943274/2147480482/715-20-55-17

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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-URI https://asc.fasb.org//715/tableOfContent

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(iii)
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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-Section 50
-Paragraph 1
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-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
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-Paragraph 1
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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-Section 50
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-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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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

Equity Investments - Investment in ATC (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Investments In ATC [Roll Forward]
Equity Investment Balance as of December 31, 2023	$ 331.2
Cash Investments	1.6	$ 0.8
Equity Earnings	5.5	6.0
Equity Investment Balance as of March 31, 2024	333.1
Net Loss Attributable to Non-Controlling Interest	(13.7)	$ (20.6)
ATC
Investments In ATC [Roll Forward]
Equity Investment Balance as of December 31, 2023	179.7
Cash Investments	1.6
Equity Earnings	5.7
Distributed earnings	(4.6)
Amortization of the Remeasurement of Deferred Income Taxes	0.3
Equity Investment Balance as of March 31, 2024	182.7
Nobles 2
Investments In ATC [Roll Forward]
Equity Investment Balance as of December 31, 2023	151.5
Equity Earnings	(0.2)
Distributed earnings	(0.9)
Equity Investment Balance as of March 31, 2024	150.4
Net Loss Attributable to Non-Controlling Interest	$ 3.0

- Definition

Amount of Net Income (Loss) attributable to noncontrolling interest.

+ References + Details

Regulatory Matters

3 Months Ended

Mar. 31, 2024

Regulated Operations [Abstract]

Regulatory Matters

REGULATORY MATTERS

Regulatory matters are summarized in Note 4. Regulatory Matters to the Consolidated Financial Statements in our 2023 Form 10-K, with additional disclosure provided in the following paragraphs.

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. Revenue from cost recovery riders was $8.3 million for the three months ended March 31, 2024 ($16.4 million for the three months ended March 31, 2023).

NOTE 2. REGULATORY MATTERS (Continued)

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 separate 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.

On May 3, 2024, Minnesota Power entered into a settlement agreement with the Minnesota Department of Commerce, Minnesota Office of the Attorney General, Residential Utilities Division, and Large Power Intervenors to settle the retail rate increase request. The settlement agreement is subject to approval by the MPUC. As part of the settlement agreement, the parties have agreed on all issues, including an overall rate increase of $33.97 million, net of rider revenue and amounts transferring to the fuel adjustment clause, a return on equity of 9.78 percent, all non-financial items and cost allocation. As a result of the settlement, Minnesota Power recorded a reserve for an interim rate refund of $5.5 million pre-tax as of March 31, 2024, which is subject to MPUC approval of the settlement agreement and Minnesota Power’s refund calculation.

2022 Minnesota General Rate Case. Minnesota Power is appealing with the Minnesota Court of Appeals (Court) specific aspects of the MPUC’s February 2023 and May 2023 rate case orders for the ratemaking treatment of Taconite Harbor and Minnesota Power’s prepaid pension asset. Oral arguments on the appeal are expected to be heard by the Court in the second quarter of 2024 with a decision expected in the third quarter of 2024. We are unable to predict the outcome of this proceeding.

2024 Wisconsin General Rate Case. On March 29, 2024, SWL&P filed a rate increase request for its electric, gas and water utilities with the PSCW. The filing seeks an overall return on equity of 10.00 percent and a 55.00 percent equity ratio. On an annualized basis, the requested change would increase rates by approximately 5.90 percent for retail customers and generate an estimated $7.3 million of additional revenue. The change to SWL&P customers’ rates will be determined by the PSCW later this year. Any rate adjustments are anticipated to become effective in January 2025.

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, and the MPUC approved Minnesota Power’s transmission factor filing with no changes in an order dated March 5, 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. Current customer billing rates for the renewable cost recovery rider were approved by the MPUC in an order dated October 3, 2023. On March 27, 2024, Minnesota Power submitted its latest renewable factor filing. If the filing is approved, Minnesota Power would be authorized to include updated billing rates on customer bills beginning October 1, 2024.

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. Current customer billing rates were approved by the MPUC 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. 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 an approximately $13 million regulatory liability as of March 31, 2024, and December 31, 2023. Minnesota Power requested to refund the regulatory liability beginning in the third quarter of 2024 as part of its annual true-up filing submitted to the MPUC on March 1, 2024.

NOTE 2. REGULATORY MATTERS (Continued)

Energy Conservation and Optimization (ECO) Plan. On April 1, 2024, Minnesota Power submitted its 2023 ECO annual filing (formerly the Conservation Improvement Plan) detailing Minnesota Power’s ECO plan results and requesting a financial incentive of $2.2 million, which will be recognized upon approval by the MPUC. In 2023, a financial incentive of $2.2 million was recognized in the third quarter upon approval by the MPUC of the 2022 ECO annual filing. The financial incentives are recognized in the period in which the MPUC approves the filing.

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. 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.


Regulatory Assets and Liabilities	March 31, 2024	December 31, 2023
Millions
Current Regulatory Assets (a)
Fuel Adjustment Clause	$8.1	$8.7
Other	0.6	0.6
Total Current Regulatory Assets	$8.7	$9.3
Non-Current Regulatory Assets
Defined Benefit Pension and Other Postretirement Plans	$217.3	$218.6
Income Taxes	85.1	88.1
Asset Retirement Obligations	38.3	37.7
Cost Recovery Riders	27.6	33.8
Taconite Harbor	18.3	20.9
Manufactured Gas Plant	13.1	13.2
PPACA Income Tax Deferral	3.9	3.9
Fuel Adjustment Clause	2.1	5.0


Other	3.3	4.2
Total Non-Current Regulatory Assets	$409.0	$425.4


Current Regulatory Liabilities (b)
Fuel Adjustment Clause	$9.0	—
Provision for Interim Rate Refund	5.5	—
Transmission Formula Rates Refund	1.0	$1.5
Other	1.6	2.4
Total Current Regulatory Liabilities	$17.1	$3.9
Non-Current Regulatory Liabilities
Income Taxes	$302.3	$310.0
Wholesale and Retail Contra AFUDC	77.3	78.0
Plant Removal Obligations	69.3	67.0
Defined Benefit Pension and Other Postretirement Benefit Plans	45.5	48.6
Non-Jurisdictional Land Sales	35.1	30.2
Investment Tax Credits	13.5	13.6
Fuel Adjustment Clause	8.2	15.5


Boswell Units 1 and 2 Net Plant and Equipment	6.7	6.7
Other	6.1	4.4
Total Non-Current Regulatory Liabilities	$564.0	$574.0

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

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

Equity Investments (Tables)

3 Months Ended

Mar. 31, 2024

Equity Method Investments and Joint Ventures [Abstract]

Equity Method Investments

We account for our investment in ATC under the equity method of accounting.


ALLETE’s Investment in ATC
Millions
Equity Investment Balance as of December 31, 2023			$179.7
Cash Investments			1.6
Equity in ATC Earnings			5.7
Distributed ATC Earnings			(4.6)
Amortization of the Remeasurement of Deferred Income Taxes			0.3
Equity Investment Balance as of March 31, 2024			$182.7

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, 2023			$151.5

Equity in Nobles 2 Earnings (a)			(0.2)
Distributed Nobles 2 Earnings			(0.9)
Equity Investment Balance as of March 31, 2024			$150.4

(a)The Company also recorded earnings from net loss attributable to non-controlling interest of $3.0 million related to its investment in Nobles 2.

Cover	3 Months Ended
Cover	Mar. 31, 2024 shares
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
Entity File Number	1-3548
Entity Registrant Name	ALLETE, Inc.
State of Incorporation	MN
Entity Tax Identification Number	41-0418150
Entity Address, Address Line One	30 West Superior Street
Entity Address, City or Town	Duluth
Entity Address, State or Province	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
Name of Exchange	NYSE
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
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	57,666,069
Entity Central Index Key	0000066756
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Amendment Flag	false

Commitments, Guarantees and Contingencies - Environmental Matters (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 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]
Redemption cost liability	$ 1

Commitments, Guarantees and Contingencies - Other Matters (Details) - USD ($) $ in Millions	Apr. 30, 2024	Mar. 31, 2024
Subsequent Event
Guarantor Obligations [Line Items]
Production tax credits sold	$ 14.0
ALLETE, Inc. \| Standby Letters of Credit
Guarantor Obligations [Line Items]
Letters of credit outstanding		$ 150.1
Regulated Operations \| Standby Letters of Credit
Guarantor Obligations [Line Items]
Letters of credit outstanding		25.4
ALLETE Clean Energy \| Standby Letters of Credit
Guarantor Obligations [Line Items]
Letters of credit outstanding		80.6
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 \| Standby Letters of Credit
Guarantor Obligations [Line Items]
Letters of credit outstanding		10.1
South Shore Energy \| Standby Letters of Credit
Guarantor Obligations [Line Items]
Letters of credit outstanding		$ 29.7

Income Tax Expense - Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense [Abstract]
Income Before Income Taxes	$ 41.0	$ 39.1
Income Taxes Computed at Statutory Federal Rate	8.6	8.2
Increase (Decrease) in Income Tax Due to:
State Income Taxes – Net of Federal Income Tax Benefit	4.6	3.4
Production tax credits	(11.6)	(10.4)
Investment tax credits	(0.3)	(2.2)
Regulatory Differences – Excess Deferred Tax	(3.5)	(2.8)
Non-Controlling Interest in Subsidiaries	2.8	3.8
AFUDC – Equity	(0.6)	(0.3)
Other	4.0	1.8
Total Income Tax Expense	$ 4.0	$ 1.5

Commitments, Guarantees and Contingencies - Power Purchase Agreements (Details) - Square Butte PPA - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Square Butte
Power Purchase Agreements [Line Items]
PPA counterparty total debt outstanding	$ 162.6
Square Butte \| Minnesota Power
Power Purchase Agreements [Line Items]
Cost of power purchased	22.9	$ 22.1
Pro rata share of PPA counterparty interest expense	$ 1.3	$ 1.3
Square Butte \| Minnesota Power \| Square Butte Coal-Fired Unit
Power Purchase Agreements [Line Items]
Expected output entitlement	50.00%
Minnkota Power \| Minnesota Power \| Square Butte Coal-Fired Unit \| Minnkota Power PSA
Power Purchase Agreements [Line Items]
Expected output entitlement	41.00%		37.00%

Fair Value - Fair Value of Financial Instruments and Assets Measured on a Nonrecurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value of Financial Instruments [Line Items]
Short-term and long-term debt - carrying amount	$ 1,797.3	$ 1,799.4
Level 2
Fair Value of Financial Instruments [Line Items]
Short-term and long-term debt - fair value	$ 1,646.8	$ 1,670.6

Operations and Significant Accounting Policies - Other Non-Current Assets (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Other Postretirement Benefit Plans	$ 104.6	$ 106.3
Contract Assets	17.9	18.5
Operating Lease Right-of-use Assets	11.3	10.7
ALLETE Properties	10.7	10.8
Restricted Cash	2.4	2.4	$ 2.3	$ 2.3
Finance Lease Right-of-use Assets	2.0	2.1
Other	115.9	112.1
Total Other Non-Current Assets	$ 264.8	$ 262.9

Earnings Per Share and Common Stock (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Basic
Net Income Attributable to ALLETE	$ 50.7	$ 58.2
Average common shares (in shares)	57.6	57.3
Earnings Per Share (in usd per share)	$ 0.88	$ 1.02
Diluted
Net Income Attributable to ALLETE	$ 50.7	$ 58.2
Average common shares adjustment (in shares)	0.1	0.0
Average common shares (in shares)	57.7	57.3
Earnings Per Share (in usd per share)	$ 0.88	$ 1.02

- 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
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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
-Topic 260
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-Publisher FASB
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
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-URI https://asc.fasb.org//1943274/2147482689/260-10-45-60B

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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+ References + Details

Consolidated Balance Sheet Unaudited - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Current Assets
Cash and Cash Equivalents	$ 32.0	$ 71.9
Accounts Receivable (Less Allowance of $1.7 and $1.6)	142.2	137.2
Inventories – Net	182.7	175.4
Prepayments and Other	76.3	83.6
Total Current Assets	433.2	468.1
Property, Plant and Equipment – Net	5,009.1	5,013.4
Regulatory Assets	409.0	425.4
Equity Investments	333.1	331.2
Goodwill and Intangible Assets – Net	155.4	155.4
Other Non-Current Assets	264.8	262.9
Total Assets	6,604.6	6,656.4
Current Liabilities
Accounts Payable	84.2	102.2
Accrued Taxes	62.9	51.0
Accrued Interest	16.3	21.1
Long-Term Debt Due Within One Year	17.2	111.4
Other	80.2	91.9
Total Current Liabilities	260.8	377.6
Long-Term Debt	1,772.4	1,679.9
Deferred Income Taxes	195.0	192.7
Regulatory Liabilities	564.0	574.0
Defined Benefit Pension and Other Postretirement Benefit Plans	135.4	160.8
Other Non-Current Liabilities	268.0	264.3
Total Liabilities	3,195.6	3,249.3
Commitments, Guarantees and Contingencies (Note 6)
Redeemable Non-Controlling Interest	0.5	0.5
Equity
Common Stock Without Par Value, 80.0 Shares Authorized, 57.7 and 57.6 Shares Issued and Outstanding	1,807.4	1,803.7
Accumulated Other Comprehensive Loss	(20.9)	(20.5)
Retained Earnings	1,036.5	1,026.4
Total ALLETE Equity	2,823.0	2,809.6
Non-Controlling Interest in Subsidiaries	585.5	597.0
Total Equity	3,408.5	3,406.6
Total Liabilities, Redeemable Non-Controlling Interest and Equity	$ 6,604.6	$ 6,656.4