Payments for Purchase of Available-for-sale Securities Payments For Purchase Of Available-For-Sale Securities Payments For Purchase Of Available-For-Sale Securities Guarantor Obligations [Line Items] Guarantor Obligations [Line Items] Statistical Measurement [Domain] Statistical Measurement [Domain] Expected Return on Plan Assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Retail Customers Retail Customers [Member] Retail Customers [Member] include residential customers, commercial customers and industrial customers. Restricted Cash included in Prepayments and Other Restricted Cash, Current Transmission Services – Utility Transmission Services - Utility Transmission Services - Utility Award Timing Predetermined Award Timing Predetermined [Flag] Component of Other Income (Expense) - Other [Domain] Component of Other Income (Expense) - Other [Domain] [Domain] for Component of Other Income (Expense) - Other [Axis] Entity File Number Entity File Number Equity Earnings Income (Loss) from Equity Method Investments Tabular List, Table Tabular List [Table Text Block] Basic Earnings Per Share, Basic [Abstract] Basis point incentive adder Basis Point Incentive Adder Basis Point Incentive Adder Schedule of Other Non-Current Liabilities Other Noncurrent Liabilities [Table Text Block] New Accounting Pronouncements and Disclosure Rules. New Accounting Pronouncements, Policy [Policy Text Block] Square Butte Square Butte [Member] Square Butte [Member] Other Other [Member] Regulated Operations Other Revenue Recognized From Other Sources Immaterial For Disaggregation Cash Contributions to Defined Benefit Pension Plans Payment for Pension Benefits Accounts Payable Increase (Decrease) in Accounts Payable Other ALLETE Clean Energy Other [Member] ALLETE Clean Energy Other Revenue Recognized From Other Sources Immaterial For Disaggregation [Member] Schedule of Fair Value of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Estimated obligation Guarantor Obligations, Maximum Exposure, Undiscounted Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Basic Earnings Per Share of Common Stock (in usd per share) Earnings Per Share (in usd per share) Earnings Per Share, Basic Adjustment to Compensation: Adjustment to Compensation [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Liabilities Liabilities, Fair Value Disclosure [Abstract] REGULATORY MATTERS Public Utilities Disclosure [Text Block] Other Income (Expense) Other Income (Expense) - Other [Line Items] [Line Items] for Other Income (Expense) - Other [Table] Total Other Comprehensive Loss Other Comprehensive Income (Loss), Net of Tax Schedule of Business Segments Schedule of Segment Reporting Information, by Segment [Table Text Block] Minnesota Power Minnesota Power [Member] Minnesota Power [Member] Power Purchase Agreements [Axis] Power Purchase Agreement - Energy and Capacity [Axis] Long-Term Contract for Purchase of Electric Power [Axis] Schedule of Cash and Cash Equivalents Schedule of Cash and Cash Equivalents [Table Text Block] Total Current Income Tax Expense Current Income Tax Expense (Benefit) Other Other Assets, Miscellaneous, Noncurrent Adjustment to Compensation, Amount Adjustment to Compensation Amount Pension Pension Plan [Member] Share-Based and ESOP Compensation Expense Share-Based Payment Arrangement, Noncash Expense Employee Stock Option Share-Based Payment Arrangement, Option [Member] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Incurred remediation costs Accrual for Environmental Loss Contingencies, Component Amount Cash, Cash Equivalents and Restricted Cash Cash and Cash Equivalents, Policy [Policy Text Block] Other Income (Expense) Other Income (Expense) - Other [Member] Other Income (Expense) - Other [Member] Common Stock Dividends Dividends, Common Stock, Cash Payments for Equity Method Investments Cash Investments Payments to Acquire Equity Method Investments Total ALLETE Equity Equity, Attributable to Parent Measurement Frequency [Axis] Measurement Frequency [Axis] Other Comprehensive Loss Other Comprehensive Income (Loss), Net of Tax [Abstract] Insider Trading Policies and Procedures [Line Items] Regulatory Proceeding [Domain] Public Utilities, Regulatory Proceeding [Domain] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Surety Bonds Surety Bond [Member] Long-term Contract Long-term Contract [Member] Long-term Contract Revenue Stream [Member] Operations And Significant Accounting Policies [Line Items] Operations And Significant Accounting Policies [Line Items] Operations And Significant Accounting Policies Minnkota Power PSA Minnkota Sales Agreement [Member] Minnkota Sales Agreement [Member] Current Assets Assets, Current [Abstract] Dividend payable period Debt Instrument, Dividend Payable Period Debt Instrument, Dividend Payable Period Rate Type [Domain] Rate Type [Domain] Rate Type [Domain] Total Liabilities, Redeemable Non-Controlling Interest and Equity Liabilities and Equity Other Current Liabilities Increase (Decrease) in Other Current Liabilities Recurring Fair Value Measures Fair Value, Recurring [Member] Natural gas project, generating production (MW) Natural Gas Project, Generating Production Natural Gas Project, Generating Production ECO Annual Filing ECO Annual Filing [Member] ECO Annual Filing Net Income (Loss) Attributable to Non-Controlling Interest Temporary Equity, Net Income Nobles 2 Nobles 2 [Member] Nobles 2 [Member] Liabilities, Redeemable Non-Controlling Interest and Equity Liabilities and Equity [Abstract] Other Income (Expense) Other Nonoperating Income (Expense) [Abstract] Cover [Abstract] Maximum Maximum [Member] Investment in ATC [Table] Equity Method Investment [Table] Net Loss Attributable to Non-Controlling Interest Net Loss Attributable to Non-Controlling Interest Net loss attributable to non-controlling interest Net Income (Loss) Attributable to Noncontrolling Interest Capital Expenditures Segment, Expenditure, Addition to Long-Lived Assets PPACA Income Tax Deferral Medicare Part D Regulatory Asset [Member] Discloses the amount of regulatory asset arising from the deferral of the retail portion of a tax charge taken in 2010 resulting from the Patient Protection and Affordable Care Act of 2010 (PPACA). PPA counterparty total debt outstanding Long-Term Contract for Purchase of Electric Power, Amount of Long-Term Debt or Lease Obligation Outstanding Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Debt Instrument [Line Items] Debt Instrument [Line Items] Collateral Guarantor Obligations, Collateral Held Directly Or By Third Parties, Amount Amount of any assets held either as collateral or by third parties that, upon the occurrence of any triggering event or condition under the guarantee, can be obtained and liquidated to recover all or a portion of the amounts paid under the guarantee. Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Pay vs Performance Disclosure [Line Items] Unamortized Debt Issuance Costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net [Abstract] Retirement Benefits [Abstract] Retirement Benefits [Abstract] Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Liabilities Liabilities [Abstract] Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Income Before Income Taxes Income Before Income Taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company Common Stock [Abstract] Common Stock, Number of Shares, Par Value and Other Disclosure [Abstract] Rate Type [Axis] Rate Type [Axis] Rate Type [Axis] including categories like electric rates, natural gas rates, water rates, etc. Other Non-Current Liabilities Total Other Non-Current Liabilities Other Liabilities, Noncurrent Financial Covenants [Table] Schedule of Long-Term Debt Instruments [Table] Sale of Renewable Development Projects Sale of Renewable Development Projects [Member] Sale of Renewable Development Projects Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Operating Segments Operating Segments [Member] Alloy Parent and Alloy Merger Sub Alloy Parent and Alloy Merger Sub [Member] Alloy Parent and Alloy Merger Sub Schedule of Supplemental Statement of Cash Flows Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Long-term PSA Long-term PSA [Member] Revenue Recognized From Long-term PSAs Industrial Industrial [Member] Industrial Sales Channel [Member] 2024 Minnesota General Rate Case 2024 Minnesota General Rate Case [Member] 2024 Minnesota General Rate Case 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 Available-For-Sale Securities, Debt Maturities, After Five Years, Fair Value Amount of available-for-sale debt securities at fair value maturing in after the fifth fiscal year following the latest fiscal year (maturing in five years or more). Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Long-Term Debt Due Within One Year Short-Term Debt Long-Term Debt, Current Maturities Company Selected Measure Amount Company Selected Measure Amount Employer contributions Defined Benefit Plan, Plan Assets, Contributions by Employer Net Loss Attributable to Non-Controlling Interest Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Changes in Regulatory and Other Non-Current Liabilities Increase (Decrease) in Other Noncurrent Liabilities Total Comprehensive Income Attributable to ALLETE Comprehensive Income (Loss), Net of Tax, Attributable to Parent Increase (Decrease) in Income Tax Due to: Increase (Decrease) in Tax [Abstract] Increase (Decrease) in Tax [Abstract] Name Measure Name Aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Distributions to Non-Controlling Interest Payments to Noncontrolling Interests 5.38% Senior Unsecured Notes Due March 2030 5.38% Senior Unsecured Notes Due March 2030 [Member] 5.38% Senior Unsecured Notes Due March 2030 Other receivables Other Receivables Deferred Income Taxes Deferred Income Tax Liabilities, Net Document Fiscal Period Focus Document Fiscal Period Focus Goodwill and Intangible Assets – Net Intangible Assets, Net (Including Goodwill) Pension and Other Postretirement Benefit Plans [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Award Timing Method Award Timing Method [Text Block] Award Type Award Type [Axis] Total Debt Long-Term Debt 2021 Integrated Resource Plan 2021 Integrated Resource Plan [Member] 2021 Integrated Resource Plan Legal Entity [Axis] Legal Entity [Axis] Total Assets Assets Assets Assets Equity Method Investment [Domain] Investment, Name [Domain] Income Taxes Deferred Income Tax Charge [Member] Trading Symbol Trading Symbol Regulatory Liability [Axis] Regulatory Liability [Axis] Amortization of PSAs Amortization Of Power Purchase Agreements The amount of income recognized in the current period that reflects income associated with the reduced liability of the PPAs acquired in a business acquisition. As noncash income, this element is subtracted from net income when calculating cash provided by or used in operations using the indirect method. Income Tax Expense Income Tax, Policy [Policy Text Block] Entity Address, City or Town Entity Address, City or Town Generating Facility Unit Name [Domain] Generating Facility Unit Name [Domain] [Domain] for Name of generating unit or facility [Axis] Asset Retirement Obligations Asset Retirement Obligation Costs [Member] Operating Activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Operations And Significant Accounting Policies [Table] Operations And Significant Accounting Policies [Table] Operations And Significant Accounting Policies Other Segment Items Segment Reporting, Other Segment Item, Amount Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Equity value of ALLETE common stock acquired Business Combination, Consideration Transferred Assets Assets, Fair Value Disclosure [Abstract] Regulatory Agency [Axis] Regulatory Agency [Axis] Entity Emerging Growth Company Entity Emerging Growth Company Power Purchase and Sale Agreements Consolidation, Variable Interest Entity, Policy [Policy Text Block] Dividends Per Share of Common Stock (in usd per share) Common Stock, Dividends, Per Share, Declared Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Total Debt Debt Issuance Costs, Net Level 2 Fair Value, Inputs, Level 2 [Member] State Income Taxes – Net of Federal Income Tax Benefit Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Equity Investments Equity Investment Balance as of December 31, 2024 Equity Investment Balance as of June 30, 2025 Equity Investment Equity Method Investments Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Alloy Parent Alloy Parent [Member] Alloy Parent Business Combination [Domain] Business Combination [Domain] Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Gain on Investments and Property, Plant and Equipment Gain (Loss) on Disposition of Other Assets Bad Debt Expense Accounts Receivable, Credit Loss Expense (Reversal) Schedule of Income Tax Expense Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] PEO PEO [Member] Regulatory Assets and Liabilities Public Utilities, Policy [Policy Text Block] Noncash Investing and Financing Activities Noncash Investing and Financing Items [Abstract] Operating and Maintenance Operating And Maintenance Operating and Maintenance Expenses Current Income Tax Expense Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Corporate and Other Corporate Segment and Other Operating Segment [Member] Changes in Operating Assets and Liabilities Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Retained Earnings Retained Earnings [Member] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Cash, Cash Equivalents and Restricted Cash at Beginning of Period Cash, Cash Equivalents and Restricted Cash at End of Period Cash, Cash Equivalents and Restricted Cash on the Consolidated Statement of Cash Flows Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Income Statement [Abstract] Income Statement [Abstract] Income Tax Expense (Benefit) Total Income Tax Expense (Benefit) Income Tax Expense (Benefit) Income Tax Expense (Benefit) Solar and wind projects, generating production (MW) Solar and Wind Projects, Generating Production Solar and Wind Projects, Generating Production Accrued Taxes Taxes Payable, Current Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Electric Rates Electric Rates [Member] Electric Rates [Member] Short-Term Debt Debt Issuance Costs, Current, Net Net Income Net Income Net Income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Total Fair Value of Liabilities Liabilities, Fair Value Disclosure Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Regulated Operations Regulated Operations [Member] Regulated Operations [Member] Guarantor Obligations [Table] Guarantor Obligation [Table] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Pension and Other Postretirement Benefit Plans [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] PSAs Power Purchase Agreement - Current Liability The fair value adjustment for the price of power per MW at market rates compared to those at contract rate at the time of acquisition through the end of the contract term present valued to acquisition date resulting in a current liability. PSAs Power Purchase Agreement - Noncurrent Liability The fair value adjustment for the price of power per MW at market rates compared to those at contract rate at the time of acquisition through the end of the contract term present valued to acquisition date resulting in a noncurrent liability. City Area Code City Area Code Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Defined Benefit Pension and Other Postretirement Benefit Plans Pension and Other Postretirement Plans Costs [Member] All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Number of states contributed to downwind states’ challenges in attaining or maintaining ozone NAAQS Accrual for Environmental Loss Contingencies, Number Of States Contributed To Downwind Challenges in Maintaining Ozone NAAQS Accrual for Environmental Loss Contingencies, Number Of States Contributed To Downwind Challenges in Maintaining Ozone NAAQS Fuel Adjustment Clause 2025 Fuel Adjustment Clause 2025 [Member] Fuel Adjustment Clause 2025 Annual additional revenue generated from requested final rate increase Public Utilities, Requested Rate Increase (Decrease), Amount Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Increase in Accounts Payable for Capital Additions to Property, Plant and Equipment Increase (Decrease) In Accounts Payable For Capital Additions To Property, Plant And Equipment Increase (Decrease) In Accounts Payable For Capital Additions To Property, Plant And Equipment Component of Other Income (Expense) - Other [Axis] Component of Other Income (Expense) - Other [Axis] Component of Other Income (Expense) - Other [Axis] Investing Activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Cash provided by Operating Activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Goodwill change Goodwill, Period Increase (Decrease) Provision (Payments) for Interim Rate Refund Provision (Payments) For Interim Rate Refund Provision (Payments) For Interim Rate Refund Equity Method Investments and Joint Ventures [Abstract] Equity Method Investments and Joint Ventures [Abstract] Amortization of Net Loss (Gain) Defined Benefit Plan, Amortization of Gain (Loss) Subsequent Event Subsequent Event [Member] Investment in ATC [Line Items] Schedule of Equity Method Investments [Line Items] Goodwill Goodwill Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Long-Term Debt, Type [Axis] Long-Term Debt, Type [Axis] Depreciation Expense Depreciation Commercial Commercial [Member] Revenue Recognized From Commercial Customers Actual ratio of indebtedness to total capitalization Debt Instrument, Actual Indebtedness to Total Capital Ratio Actual indebtedness to total capital ratio required to be maintained by most restrictive financial covenant. States were EPA issued an updated final interim rule addressing the stays Accrual for Environmental Loss Contingencies, Number States Is In EPA Stay Accrual for Environmental Loss Contingencies, Number States Is In EPA Stay Federal Deferred Federal Income Tax Expense (Benefit) Equity Components [Axis] Equity Components [Axis] Standby Letters of Credit Standby Letters of Credit [Member] AFUDC – Equity Effective Income Tax Rate Reconciliation, Tax Expense (Benefit), Share-Based Payment Arrangement, Amount Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Environmental Matters [Line Items] Environmental Matters [Line Items] [Line Items] for Environmental Matters [Table] Number of reportable segments Number of Reportable Segments Energy storage project, generating production (MW) Energy Storage Project, Generating Production Energy Storage Project, Generating Production Power Purchase Agreements [Line Items] Long-Term Contract for Purchase of Electric Power [Line Items] Manufactured Gas Plant Manufactured Gas Plant [Member] Manufactured Gas Plant [Member] Production tax credits sold Guarantor Obligations, Production Tax Credits Sold Guarantor Obligations, Production Tax Credits Sold OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Other Performance Measure, Amount Other Performance Measure, Amount Schedule of Restrictions on Cash and Cash Equivalents Restrictions on Cash and Cash Equivalents [Table Text Block] Regulatory Liabilities Total Non-Current Regulatory Liabilities Regulatory Liability, Noncurrent Entity Address, State or Province Entity Address, State or Province Generating capacity (MW) Anticipated Additional Generating Capacity (MW) Anticipated Additional Generating Capacity (MW) Fair Value Fair Value Measurement, Policy [Policy Text Block] Total Current Liabilities Liabilities, Current Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense [Abstract] Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract] Individual: Individual [Axis] Fuel, Purchased Power and Gas – Utility Fuel, Purchased Power and Gas - Utility Fuel, Purchased Power and Gas - Utility Dividends on Common Stock Payments of Ordinary Dividends, Common Stock Prepayments and Other Prepayments and other Other Assets, Current Investments Investments [Abstract] Entity [Domain] Entity [Domain] Other Power Suppliers Other Power Suppliers [Member] Other Power Suppliers Sales Channel [Member] Cash used in Investing Activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Short-Term Debt Long-Term Debt, Current Maturities, Gross Amount of short-term debt and current maturities of long-term debt before deduction of unamortized discount or premium and unamortized debt issuance costs. Cash Paid for Interest – Net of Amounts Capitalized Interest Paid, Excluding Capitalized Interest, Operating Activity Proceeds from Non-Controlling Interest in Subsidiaries – Net Proceeds from Noncontrolling Interests Document Fiscal Year Focus Document Fiscal Year Focus Expected period for costs of compliance Expected Period For Costs Of Compliance Expected Period For Costs Of Compliance Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Investment Tax Credit Amortization Deferred Other Tax Expense (Benefit) Amortization of Other Intangible Assets and Other Assets Other Depreciation and Amortization Repayments of Short-Term and Long-Term Debt Repayments of Long-Term Debt Effective tax rate Effective Income Tax Rate Reconciliation, Percent Environmental Remediation Contingency [Axis] Environmental Remediation Contingency [Axis] Entity Interactive Data Current Entity Interactive Data Current Fuel Adjustment Clause Regulatory Clause Revenues, under-Recovered [Member] ALLETE, Inc. ALLETE, Inc. [Member] -- None. No documentation exists for this element. -- Cash Equivalents Other Restricted Assets, Noncurrent Square Butte PPA Square Butte PPA [Member] Long-term contract with Square Butte for the purchase of electric power. ALLETE Properties Real Estate Investments, Net New Energy New Energy [Member] New Energy BUSINESS SEGMENTS Segment Reporting Disclosure [Text Block] Recurring Fair Value Measures [Abstract] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Maturity Date [Domain] Maturity Date [Domain] Maturity Date Dividend payable percentage limit Debt Instrument, Dividend Payable Percentage Limit Debt Instrument, Dividend Payable Percentage Limit Federal Current Federal Tax Expense (Benefit) Consolidated Statement of Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Fuel Adjustment Clause 2024 Fuel Adjustment Clause 2024 [Member] Fuel Adjustment Clause 2024 Approved rate increase Public Utilities, Approved Rate Increase (Decrease), Amount Cost of power purchased Utilities Operating Expense, Purchased Power under Long-Term Contracts Schedule of Components in Net Periodic Benefit Cost (Credit) Schedule of Net Benefit Costs [Table Text Block] Defined Benefit Pension and Other Postretirement Plan Benefit Pension and Other Postretirement Benefits Expense (Reversal of Expense), Noncash Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Wind project, generating production (MW) Wind Project, Generating Production Wind Project, Generating Production Recurring Fair Value Measures [Table] Fair Value, Recurring and Nonrecurring [Table] Wholesale and Retail Contra AFUDC Wholesale and Retail Contra AFUDC [Member] Wholesale and Retail Contra AFUDC [Member] Depreciation and Amortization Depreciation and Amortization Depreciation, Depletion and Amortization Cost Recovery Riders Cost Recovery Riders [Member] Cost Recovery Riders [Member] Other Non-Current Assets Total Other Non-Current Assets Other Assets, Noncurrent Accrued Interest Interest Payable, Current Entity Central Index Key Entity Central Index Key PEO Name PEO Name Total Operating Revenue Total Operating Revenue Revenues Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Fair Value of Financial Instruments [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Natural Gas Capacity Natural Gas Capacity [Member] Natural Gas Capacity Plant Removal Obligations Removal Costs [Member] Approximate annual reduction in pretax income for FERC proposal to limit incentive adder, Allete's proportionate share Approximate Annual Reduction In Pretax Income For FERC Proposal To Limit Incentive Adder, ALLETE's Proportionate Share Approximate Annual Reduction In Pretax Income For FERC Proposal To Limit Incentive Adder, ALLETE's Proportionate Share Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Contracts with Customers – Non-utility Unregulated Operating Revenue Wind Turbine Generators Wind Turbine Generators [Member] Wind Turbine Generators [Member] Arrangement Duration Trading Arrangement Duration Business Segments [Table] Schedule of Segment Reporting Information, by Segment [Table] Customer Deposits Contract with Customer, Liability, Current Business Segments [Axis] Segments [Axis] Balance, Beginning of Period Total Redeemable Non-Controlling Interest Temporary Equity, Carrying Amount, Attributable to Parent Prepayments and Other Increase (Decrease) in Prepaid Expense and Other Assets Tenaska Tenaska [Member] Tenaska Energy, Inc. and Tenaska Energy Holdings, LLC [Member] Exercise Price Award Exercise Price Power Purchase Agreements [Domain] Power Purchase Agreement - Energy and Capacity [Domain] Long-Term Contract for Purchase of Electric Power [Domain] Fuel Energy Related Inventory, Coal Entity Filer Category Entity Filer Category Local Phone Number Local Phone Number Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Statutory Federal Income Tax Rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Contract Assets Contract with Customer, Asset, after Allowance for Credit Loss, Noncurrent Other Investing Activities Payment for (Proceeds from) Other Investing Activity Subsequent Event Type [Axis] Subsequent Event Type [Axis] Number of states restricted on certain industrial sources Accrual for Environmental Loss Contingencies, Number Of States Restricted On Certain Industrial Sources Accrual for Environmental Loss Contingencies, Number Of States Restricted On Certain Industrial Sources Generation Type [Axis] Generation Type [Axis] Generation Type [Axis] BNI Energy BNI Energy [Member] BNI Energy Assets Assets [Abstract] Investments In ATC [Roll Forward] Investments In ATC [Roll Forward] Investments In ATC Long-Term Debt Long-Term Debt Long-Term Debt, Excluding Current Maturities Underlying Security Market Price Change Underlying Security Market Price Change, Percent Components of Net Periodic Benefit Cost (Credit) Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] Bonds Bonds [Member] Debt Instrument [Axis] Debt Instrument [Axis] PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS Retirement Benefits [Text Block] FAIR VALUE Fair Value Disclosures [Text Block] ALLETE Equity Equity, Attributable to Parent [Abstract] Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Entity Address, Address Line One Entity Address, Address Line One Redeemable Non-Controlling Interest Temporary Equity, Including Noncontrolling Interest Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Interest rate Interest Rate Debt Instrument, Interest Rate, Stated Percentage Equity Method Investment [Axis] Investment, Name [Axis] Accounts receivable, less allowance Accounts Receivable, Allowance for Credit Loss, Current Amortization of Prior Service Credits Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] COMMITMENTS, GUARANTEES AND CONTINGENCIES Commitments Contingencies and Guarantees [Text Block] Fuel, Purchased Power and Gas – Utility Fuel, Purchased Power And Gas - Utility Fuel, Purchased Power And Gas - Utility Coal Combustion Residuals Coal Combustion Residuals [Member] Coal Combustion Residuals [Member] Fair Value as of Grant Date Award Grant Date Fair Value Proceeds from Non-Controlling Interest in Subsidiaries Temporary Equity, Interest in Subsidiary Earnings Entity Registrant Name Entity Registrant Name Changes in Regulatory and Other Non-Current Assets Increase (Decrease) in Other Noncurrent Assets Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Net Periodic Benefit Cost (Credit) Defined Benefit Plan, Net Periodic Benefit Cost (Credit) ATC ATC [Member] ATC [Member] Schedule of Other Income (Expense) Schedule of Other Nonoperating Income (Expense) [Table Text Block] Taxes Other than Income Taxes Taxes, Other Schedule of Long-Term Debt Instruments Schedule of Long-Term Debt Instruments [Table Text Block] Contracts with Customers – Utility Regulated Operating Revenue Total Operating Expenses Costs and Expenses Regulated Operations [Abstract] Regulated Operations [Abstract] Guarantee Entity and Type [Domain] Guarantee Entity and Type [Domain] [Domain] for Guarantee Entity and Type [Axis] Document Quarterly Report Document Quarterly Report Total Fair Value of Assets Assets, Fair Value Disclosure Short-term and long-term debt - fair value Long-Term Debt, Fair Value Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Counterparty Name [Domain] Counterparty Name [Domain] Number of operating segments Number of Operating Segments Provision for Interim Rate Refund Public Utilities Reserve for Interim Rates Public Utilities Reserve for Interim Rates Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Estimated costs of compliance Site Contingency, Loss Exposure Not Accrued, Best Estimate Requested return on equity Public Utilities, Requested Return on Equity, Percentage Schedule of Short-Term and Long-Term Debt Schedule of Debt [Table Text Block] Maximum conversion window Common Stock, Convertible, Maximum Conversion Window Common Stock, Convertible, Maximum Conversion Window Interest Cost Defined Benefit Plan, Interest Cost Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Renewable Energy Facilities Under Development Other Inventory, Gross Restatement Determination Date: Restatement Determination Date [Axis] Minnkota Power Minnkota Power [Member] Minnkota Power [Member] Requested rate increase percent Public Utilities, Requested Rate Increase (Decrease), Percentage Non-PEO NEO Non-PEO NEO [Member] Letters of credit outstanding Letters of Credit Outstanding, Amount Proceeds from Non-Controlling Interest in Subsidiaries – Net Noncontrolling Interest, Increase from Subsidiary Equity Issuance Other Financing Activities Proceeds from (Payment for) Other Financing Activity Regulatory Asset [Axis] Regulatory Asset [Axis] Name Trading Arrangement, Individual Name All Award Types Award Type [Domain] Interest and Investment Income Interest and Investment Earnings [Member] Interest and Investment Earnings [Member] Short-Term Debt [Table] Short-Term Debt [Table] Non-Controlling Interest in Subsidiaries Equity, Attributable to Noncontrolling Interest Equity Awards Adjustments Equity Awards Adjustments [Member] Guarantee Entity and Type [Axis] Guarantee Entity and Type [Axis] Guarantee Entity and Type [Axis] Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Accounts Receivable Increase (Decrease) in Accounts and Other Receivables Compensation Amount Outstanding Recovery Compensation Amount Deferred Income Tax Expense (Benefit) Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract] Debt instrument, face amount Principal Amount Debt Instrument, Face Amount Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Aggregate amount of available-for-sale corporate and governmental debt securities maturing after one year through three years after three years through five years Available-For-Sale Securities, Debt Maturities, After Three Years Through Five Years, Fair Value Amount of available-for-sale debt securities at fair value maturing after the third fiscal year through the fifth fiscal year following the latest fiscal year (maturing in three years to less than five years). 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