PPA counterparty total debt outstanding Long-Term Contract for Purchase of Electric Power, Amount of Long-Term Debt or Lease Obligation Outstanding Payments for Purchase of Available-for-sale Securities Payments For Purchase Of Available-For-Sale Securities Payments For Purchase Of Available-For-Sale Securities Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Net Loss Attributable to Non-Controlling Interest Net Loss Attributable to Non-Controlling Interest Net Income (Loss) Attributable to Noncontrolling Interest Pay vs Performance Disclosure [Line Items] Statistical Measurement [Domain] Statistical Measurement [Domain] Line of credit Line of Credit Facility, Maximum Borrowing Capacity Changes in Operating Assets and Liabilities Increase (Decrease) in Operating Capital [Abstract] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Retail Customers Retail Customers [Member] Retail Customers [Member] include residential customers, commercial customers and industrial customers. Transmission Services – Utility Transmission Services - Utility Transmission Services - Utility Component of Other Income (Expense) - Other [Domain] Component of Other Income (Expense) - Other [Domain] [Domain] for Component of Other Income (Expense) - Other [Axis] Regulatory Matters Public Utilities Disclosure [Text Block] All Award Types Award Type [Domain] Fair Value as of Grant Date Award Grant Date Fair Value Equity Method Investment [Domain] Investment, Name [Domain] Income Taxes Deferred Income Tax Charge [Member] Uncertain Tax Positions Income Tax Uncertainties, Policy [Policy Text Block] Short-Term and Long-Term Debt Debt Disclosure [Text Block] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Basis point incentive adder Basis Point Incentive Adder Basis Point Incentive Adder Cash Contributions to Defined Benefit Pension Plans Payment for Pension Benefits Expected output entitlement Long-Term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased Square Butte Square Butte [Member] Square Butte [Member] Other Other [Member] Regulated Operations Other Revenue Recognized From Other Sources Immaterial For Disaggregation Equity Method Investments and Joint Ventures [Abstract] Equity Method Investments and Joint Ventures [Abstract] MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Other ALLETE Clean Energy Other [Member] ALLETE Clean Energy Other Revenue Recognized From Other Sources Immaterial For Disaggregation [Member] Fuel Energy Related Inventory, Coal Segment Reporting [Abstract] Segment Reporting [Abstract] Accounts Payable Accounts Payable, Current Restatement Determination Date: Restatement Determination Date [Axis] Equity Method Investment [Axis] Investment, Name [Axis] Changes in Regulatory and Other Non-Current Liabilities Increase (Decrease) in Other Noncurrent Liabilities Total Other Income (Expense) Nonoperating Income (Expense) Commitments, Guarantees and Contingencies (Note 6) Commitments and Contingencies Insider Trading Policies and Procedures [Line Items] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Fuel Adjustment Clause 2022 Fuel Adjustment Clause 2022 [Member] Fuel Adjustment Clause 2022 Other Income Other Income (Expense) - Other [Line Items] [Line Items] for Other Income (Expense) - Other [Table] Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Proceeds from Issuance of Common Stock Proceeds from Issuance of Common Stock Changes in Regulatory and Other Non-Current Assets Increase (Decrease) in Other Noncurrent Assets Conservation improvement program goal, next fiscal year Energy Conservation and Optimization Plan Goal, Next Fiscal Year Energy Conservation and Optimization Plan Goal, Next Fiscal Year Geographical [Axis] Geographical [Axis] Minnesota Power Minnesota Power [Member] Minnesota Power [Member] Other Other Regulatory Assets (Liabilities) [Member] Generating capacity subject to tax equity financing Generating Capacity Subject To Tax Equity Financing Generating Capacity Subject To Tax Equity Financing Income Tax Expense Income Tax Disclosure [Text Block] Other Other Accrued Liabilities, Noncurrent Current Liabilities Liabilities, Current [Abstract] Federal Deferred Federal Income Tax Expense (Benefit) Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Axis] Unamortized Debt Issuance Costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net [Abstract] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Recurring Fair Value Measures [Table] Fair Value, Recurring and Nonrecurring [Table] Other Other Income (Expense) - Other [Member] Other Income (Expense) - Other [Member] Dividends on Common Stock Payments of Ordinary Dividends, Common Stock Diluted Earnings Per Share of Common Stock (in usd per share) Earnings Per Share (in usd per share) Earnings Per Share, Diluted Cash Equivalents Other Restricted Assets, Noncurrent PEO Total Compensation Amount PEO Total Compensation Amount Accounts Receivable (Less Allowance of $1.5 and $1.6) Accounts Receivable, after Allowance for Credit Loss, Current Customer refund Customer Refund Liability, Current Long-term Contract Long-term Contract [Member] Long-term Contract Revenue Stream [Member] Minnkota Power PSA Minnkota Sales Agreement [Member] Minnkota Sales Agreement [Member] Rate Type [Domain] Rate Type [Domain] Rate Type [Domain] Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Level 3 Fair Value, Inputs, Level 3 [Member] Line of Credit Line of Credit [Member] Proceeds from issuance of first mortgage bond Proceeds from Issuance of First Mortgage Bond Total Current Regulatory Assets Regulatory Asset, Current Components of Net Periodic Benefit Cost (Credit) Schedule of Net Benefit Costs [Table Text Block] Nobles 2 Nobles 2 [Member] Nobles 2 [Member] Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] Other Income (Expense) Other Nonoperating Income (Expense) [Abstract] PSA Liability PSA Liability [Member] PSA Liability Fuel Adjustment Clause Increase (Decrease) in Regulatory Clause Revenue Trading Symbol Trading Symbol Letters of credit outstanding Letters of Credit Outstanding, Amount Payments for Equity Method Investments Cash Investments Payments to Acquire Equity Method Investments Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Power Purchase Agreements [Domain] Power Purchase Agreement - Energy and Capacity [Domain] Long-Term Contract for Purchase of Electric Power [Domain] Short-term and long-term debt - fair value Long-Term Debt, Fair Value Unrealized gain (loss) on securities, income tax expense OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment, Tax Net Income Attributable to ALLETE Net Income Attributable to ALLETE Net Income (Loss) Attributable to ALLETE Net Income (Loss) Total Current Liabilities Liabilities, Current Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] 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). Requested equity capital structure Public Utilities, Requested Equity Capital Structure, Percentage Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Company Selected Measure Name Company Selected Measure Name Accrued Interest Interest Payable, Current 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 occurence 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. Liabilities and Equity Liabilities and Equity [Abstract] Investment in ATC [Table] Schedule of Equity Method Investments [Table] Equity Equity, Attributable to Parent [Abstract] Other Other Assets, Miscellaneous, Noncurrent Reconciliation of Basic and Diluted Earnings Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Cost of Sales – Non-utility Cost of Goods and Services Sold Service Cost Defined Benefit Plan, Service Cost Rate Type [Axis] Rate Type [Axis] Rate Type [Axis] including categories like electric rates, natural gas rates, water rates, etc. Executive Category: Executive Category [Axis] Sale of Renewable Development Projects Sale of Renewable Development Projects [Member] Sale of Renewable Development Projects Revenue Streams [Axis] Contract with Customer, Sales Channel [Axis] Purchase price accounting impact Purchase Price Accounting Impact Purchase Price Accounting Impact. Expense (benefit) as a result of purchase price accounting. Long-term PSA Long-term PSA [Member] Revenue Recognized From Long-term PSAs Level 1 Fair Value, Inputs, Level 1 [Member] Name Measure Name Industrial Industrial [Member] Industrial Sales Channel [Member] Issuable letters of credit Line of Credit Facility, Current Borrowing Capacity 2024 Minnesota General Rate Case 2024 Minnesota General Rate Case [Member] 2024 Minnesota General Rate Case Name Forgone Recovery, Individual Name 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). Estimated obligation Guarantor Obligations, Maximum Exposure, Undiscounted Goodwill Goodwill Increase (Decrease) in Income Tax Due to: Increase (Decrease) in Tax [Abstract] Increase (Decrease) in Tax [Abstract] Equity Components [Axis] Equity Components [Axis] Return on common equity Public Utilities, Approved Equity Capital Structure, Percentage Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Underlying Securities Award Underlying Securities Amount Entity Small Business Entity Small Business Sale of Wind Energy Facilities Sale of Wind Energy Facility [Member] Sale of Wind Energy Facility Local Phone Number Local Phone Number Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Dividends Per Share of Common Stock (in usd per share Common Stock, Dividends, Per Share, Declared Net of Income Tax Expense (Benefit) of $—, $—, $0.1 and $(0.2) Unrealized Gain (Loss) on Debt Securities OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax Measurement Frequency [Axis] Measurement Frequency [Axis] Materials and Supplies Inventory, Supplies, Net of Reserves Operating Lease Liabilities Operating Lease, Liability, Noncurrent Retirement Plan Type [Domain] Retirement Plan Type [Domain] Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Defined Benefit Pension and Other Postretirement Plans Defined Benefit Pension and Other Postretirement Benefit Plans Pension and Other Postretirement Plans Costs [Member] Equity Issuance Costs Payments of Stock Issuance Costs Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Depreciation Expense Depreciation Retirement Benefits [Abstract] Retirement Benefits [Abstract] Other – Non-utility 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. Generating Facility Unit Name [Domain] Generating Facility Unit Name [Domain] [Domain] for Name of generating unit or facility [Axis] Defined Benefit Pension and Other Postretirement Benefit Plans Liability, Defined Benefit Plan, Noncurrent Gross proceeds from arbitration Proceeds From Legal Settlements, Gross Proceeds From Legal Settlements, Gross Goodwill and Intangible Assets – Net Intangible Assets, Net (Including Goodwill) Regulatory Matters [Line Items] Public Utilities, General Disclosures [Line Items] Average common shares adjustment (in shares) Weighted Average Number of Shares Outstanding, Diluted, Adjustment Equity Method Investments Equity Method Investments [Table Text Block] Power Purchase Agreements [Axis] Power Purchase Agreement - Energy and Capacity [Axis] Long-Term Contract for Purchase of Electric Power [Axis] Cash, Cash Equivalents and Restricted Cash Cash and Cash Equivalents, Policy [Policy Text Block] Power Purchase and Sale Agreements Consolidation, Variable Interest Entity, Policy [Policy Text Block] Total Operating Revenue Total Operating Revenue Revenues Fair Value of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Regulatory Assets and Liabilities Public Utilities, Policy [Policy Text Block] Other Performance Measure, Amount Other Performance Measure, Amount Superior, WI Superior, WI [Member] Superior, WI Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Inventories Increase (Decrease) in Inventories Standby Letters of Credit Standby Letters of Credit [Member] Investing Activities Net Cash Provided by (Used in) Investing Activities [Abstract] Common Stock [Abstract] Common Stock, Number of Shares, Par Value and Other Disclosure [Abstract] Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Transaction costs Business Combination, Acquisition Related Costs Award Type Award Type [Axis] Document Quarterly Report Document Quarterly Report Noncash Investing and Financing Activities Noncash Investing and Financing Items [Abstract] Interest Expense Interest Expense Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Operating and Maintenance Operating And Maintenance Operating and Maintenance Expenses Trading Arrangement: Trading Arrangement [Axis] Diamond Spring Diamond Spring [Member] Diamond Spring [Member] Employer contributions Defined Benefit Plan, Plan Assets, Contributions by Employer PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Expected Return on Plan Assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Long-Term Debt Unamortized Debt Issuance Expense, Long-Term Debt Excluding Current Maturities The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of long-term debt excluding current maturities. Non-Controlling Interest Details [Line Items] Non-Controlling Interest Details [Line Items] [Line Items] for Non-Controlling Interest Details [Table] Income Tax Expense Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Long-Term Debt, Type [Domain] Long-Term Debt, Type [Domain] Entity File Number Entity File Number Non-Controlling Interest Details [Table] Non-Controlling Interest Details [Table] Non-Controlling Interest Details [Table] Operating Lease Liabilities Operating Lease, Liability, Current Entity Shell Company Entity Shell Company Manufactured Gas Plant - Current Manufactured Gas Plant - Current Manufactured Gas Plant - Current Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Restatement Determination Date Restatement Determination Date Counterparty Name [Domain] Counterparty Name [Domain] Requested return on equity Public Utilities, Requested Return on Equity, Percentage Electric Rates Electric Rates [Member] Electric Rates [Member] Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Regulatory Agency [Domain] Regulatory Agency [Domain] 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 Equivalents, Restricted Cash, and Restricted Cash Equivalents Subsequent Events Subsequent Events, Policy [Policy Text Block] Regulated Operations Regulated Operations [Member] Regulated Operations [Member] Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Common stock, shares issued (in shares) Common Stock, Shares, Issued 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. Customer Deposits Contract with Customer, Liability, Current 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. Authorized return on equity, including incentive adder Equity Method Investment, Approved Return on Common Equity, Including Incentive Adder The approved percentage return on common equity, including an incentive adder for participation in a regional transmission organization dedicated to the utility plant in the investee accounted for under the equity method of accounting. Contracts with Customers – Utility Regulated Operating Revenue Name of Exchange Security Exchange Name Short-term and long-term debt - carrying amount Long-Term Debt Total Fair Value of Assets Assets, Fair Value Disclosure Capitalized Asset Retirement Costs Increase (Decrease) in Asset Retirement Obligations Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Income (Loss), Net of Tax Employee Stock Option Employee Stock Option [Member] Investment tax credits Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount 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 Pro rata share of PPA counterparty interest expense Long-Term Contract for Purchase of Electric Power, Interest Included in Contract Charges Component of Other Income (Expense) - Other [Axis] Component of Other Income (Expense) - Other [Axis] Component of Other Income (Expense) - Other [Axis] Plant Removal Obligations Removal Costs [Member] Total Operating Expenses Costs and Expenses Other Financing Activities Proceeds from (Payments for) Other Financing Activities Maximum Maximum [Member] Total Comprehensive Income Attributable to ALLETE Comprehensive Income (Loss), Net of Tax, Attributable to Parent Document Type Document Type Regulatory Agency [Axis] Regulatory Agency [Axis] Tabular List, Table Tabular List [Table Text Block] Cost of power purchased Utilities Operating Expense, Purchased Power under Long-Term Contracts Entity Address, Address Line One Entity Address, Address Line One Inventories – Net Inventory, Policy [Policy Text Block] 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. Federal Current Federal Tax Expense (Benefit) Arbitration costs recovery Litigation Settlement, Amount Awarded From Other Party, Arbitration Costs Recovery Litigation Settlement, Amount Awarded From Other Party, Arbitration Costs Recovery Environmental Matters [Line Items] Environmental Matters [Line Items] [Line Items] for Environmental Matters [Table] Business Acquisition [Axis] Business Acquisition [Axis] Accrued Taxes Taxes Payable, Current Fair Value of Financial Instruments [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Manufactured Gas Plant Manufactured Gas Plant [Member] Manufactured Gas Plant [Member] Accounts Receivable (Less Allowance of $1.5 and $1.6) Accounts Receivable, Allowance for Credit Loss, Current Subsequent Event Subsequent Event [Member] Regulatory Proceeding [Domain] Public Utilities, Regulatory Proceeding [Domain] Restricted Cash included in Other Non-Current Assets Restricted Cash Restricted Cash, Noncurrent State Deferred State and Local Income Tax Expense (Benefit) Other Total Other Current Liabilities Other Liabilities, Current Short-Term Debt Debt, Current, 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. Income Statement [Abstract] Income Statement [Abstract] ALLETE Bonds 4.98% Due April 2033 ALLETE Bonds 4.98% Due April 2033 [Member] ALLETE Bonds 4.98% Due April 2033 Title of 12(b) Security Title of 12(b) Security Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Components of Net Periodic Benefit Cost (Credit) [Abstract] Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] Pension and Other Postretirement Benefit Plans [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Operating Segments Operating Segments [Member] Prepayments and Other Other Assets, Current Environmental Matters Environmental Costs, Policy [Policy Text Block] Other Power Suppliers Other Power Suppliers [Member] Other Power Suppliers Sales Channel [Member] Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Income Taxes Computed at Statutory Federal Rate Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Distributions to Non-Controlling Interest Payments to Noncontrolling Interests Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Diluted Earnings Per Share, Diluted [Abstract] Expected period for costs of compliance Expected Period For Costs Of Compliance Expected Period For Costs Of Compliance Entity Tax Identification Number Entity Tax Identification Number Equity Investments Equity Investment Balance as of December 31, 2022 Equity Investment Balance as of September 30, 2023 Equity Method Investments Total Debt Debt, Long-Term and Short-Term, Combined Amount Inventories – Net Inventories – Net Inventory, Net Statistical Measurement [Axis] Statistical Measurement [Axis] Operating revenue, other than customer revenue Revenue, Other Than Customer Revenue Non-cash Revenue Recognized From Amortization of PSAs Assumed Through Acquisitions ALLETE, Inc. ALLETE, Inc. [Member] -- None. No documentation exists for this element. -- Entity Interactive Data Current Entity Interactive Data Current Arbitration Award Arbitration Award [Member] Arbitration Award Short-Term Debt Unamortized Debt Issuance Expense, Debt, Current The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of short-term debt or the current maturities of long-term debt. Square Butte PPA Square Butte PPA [Member] Long-term contract with Square Butte for the purchase of electric power. New Energy New Energy [Member] New Energy Total Shareholder Return Amount Total Shareholder Return Amount Cash, Cash Equivalents and Restricted Cash [Abstract] Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents [Abstract] Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Deferred Income Taxes Deferred Income Taxes and Other Tax Liabilities, Noncurrent Defined benefit pension and other postretirement benefit plans, income tax expense Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax Business Segments [Domain] Segments [Domain] Residential Interim Rate Adjustment Increase (Decrease) for Residential Interim Rate Adjustment Increase (Decrease) for Residential Interim Rate Adjustment Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Other Income Schedule of Other Nonoperating Income (Expense) [Table Text Block] Consolidation Items [Domain] Consolidation Items [Domain] Retained Earnings Retained Earnings (Accumulated Deficit) Measure: Measure [Axis] Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Name Outstanding Recovery, Individual Name State of Incorporation Entity Incorporation, State or Country Code Current Assets Assets, Current [Abstract] Wholesale and Retail Contra AFUDC Wholesale and Retail Contra AFUDC [Member] Wholesale and Retail Contra AFUDC [Member] Cost Recovery Riders Cost Recovery Riders [Member] Cost Recovery Riders [Member] Entity Address, State or Province Entity Address, State or Province Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Counterparty Name [Axis] Counterparty Name [Axis] North Dakota Investment Tax Credits North Dakota Investment Tax Credits Subject to Refund [Member] North Dakota Investment Tax Credits Subject to Refund [Member] Operating Activities Net Cash Provided by (Used in) Operating Activities [Abstract] Guarantor Obligations [Line Items] Guarantor Obligations [Line Items] 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 Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Wind Turbine Generators Wind Turbine Generators [Member] Wind Turbine Generators [Member] Environmental Remediation Contingency [Axis] Environmental Remediation Contingency [Axis] Basic Earnings Per Share, Basic [Abstract] Interest Cost Defined Benefit Plan, Interest Cost Accounts Receivable Increase (Decrease) in Accounts and Other Receivables PEO PEO [Member] Other Receivables Other Receivables Pension and Other Postretirement Benefit Plans Retirement Benefits [Text Block] Tenaska Tenaska [Member] Tenaska Energy, Inc. and Tenaska Energy Holdings, LLC [Member] Contract Assets Contract with Customer, Asset, after Allowance for Credit Loss, Noncurrent State Income Taxes – Net of Federal Income Tax Benefit Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Generation Type [Axis] Generation Type [Axis] Generation Type [Axis] BNI Energy BNI Energy [Member] BNI Energy Cash used in Investing Activities Net Cash Provided by (Used in) Investing Activities Investments In ATC [Roll Forward] Investments In ATC [Roll Forward] Investments In ATC Net Income Attributable to ALLETE Net Income (Loss) Available to Common Stockholders, Basic Energy conservation and optimization plan goal, second fiscal year Energy Conservation and Optimization Plan Goal, Second Fiscal Year Energy Conservation and Optimization Plan Goal, Second Fiscal Year Inventories – Net Schedule of Inventory, Current [Table Text Block] Other Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount Expected future employer contributions Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year Debt Instrument [Axis] Debt Instrument [Axis] Contracts with Customers – Non-utility Unregulated Operating Revenue Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Effective tax rate Effective Income Tax Rate Reconciliation, Percent Proceeds from Non-Controlling Interest in Subsidiaries – Net Noncontrolling Interest, Increase from Subsidiary Equity Issuance 2022 Minnesota General Rate Review 2022 Minnesota General Rate Review [Member] 2022 Minnesota General Rate Review Annual additional revenue generated from requested final rate increase Public Utilities, Requested Rate Increase (Decrease), Amount Total Liabilities Liabilities Total Current Income Tax Expense Current Income Tax Expense (Benefit) Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Prepayments and Other Increase (Decrease) in Prepaid Expense and Other Assets Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Measurement Frequency [Domain] Measurement Frequency [Domain] All Executive Categories All Executive Categories [Member] Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Fuel, Purchased Power and Gas – Utility Fuel, Purchased Power And Gas - Utility Fuel, Purchased Power And Gas - Utility Reclassification of Property, Plant and Equipment to Inventory Reclassification of Property, Plant and Equipment to Inventory Reclassification of Property, Plant and Equipment to Inventory Coal Combustion Residuals Coal Combustion Residuals [Member] Coal Combustion Residuals [Member] Debt Disclosure [Abstract] Debt Disclosure [Abstract] Number of reportable segments Number of Reportable Segments ATC ATC [Member] ATC [Member] Fuel Adjustment Clause 2023 Fuel Adjustment Clause 2023 [Member] Fuel Adjustment Clause 2023 Earnings Per Share [Abstract] Earnings Per Share [Abstract] Total Regulatory Asset [Domain] Regulatory Asset [Domain] Common Stock Without Par Value, 80.0 Shares Authorized, 57.5 and 57.2 Shares Issued and Outstanding Common Stock, Value, Issued Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Guarantee Entity and Type [Domain] Guarantee Entity and Type [Domain] [Domain] for Guarantee Entity and Type [Axis] Additional revenue from base rates Public Utilities, Approved Rate Increase (Decrease), Amount Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] State Current State and Local Tax Expense (Benefit) Business Segments Segment Reporting, Policy [Policy Text Block] Total Current Assets Assets, Current Deferred Income Tax Expense (Benefit) Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract] Provision for Interim Rate Refund Public Utilities Reserve for Interim Rates Public Utilities Reserve for Interim Rates Net Periodic Benefit Cost (Credit) Defined Benefit Plan, Net Periodic Benefit Cost (Credit) All Individuals All Individuals [Member] Other Total Other Income Other Nonoperating Income (Expense) Entity Filer Category Entity Filer Category Investment in ATC [Line Items] Schedule of Equity Method Investments [Line Items] Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Minnkota Power Minnkota Power [Member] Minnkota Power [Member] Consolidated Statement of Equity [Table] Statement [Table] Current Fiscal Year End Date Current Fiscal Year End Date Earnings Per Share and Common Stock Earnings Per Share, Policy [Policy Text Block] Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Defined Benefit Pension and Postretirement Benefit Pension and Other Postretirement Benefits Expense (Reversal of Expense), Noncash Gross unrecognized tax benefits Unrecognized Tax Benefits PEO Name PEO Name Fair Value of Financial Instruments [Table] Fair Value, by Balance Sheet Grouping [Table] Current Income Tax Expense Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Interest and Investment Income (b) Interest and Investment Earnings [Member] Interest and Investment Earnings [Member] Restricted Cash included in Prepayments and Other Restricted Cash, Current Regulatory Liabilities Total Non-Current Regulatory Liabilities Regulatory Liability, Noncurrent Guarantee Entity and Type [Axis] Guarantee Entity and Type [Axis] Guarantee Entity and Type [Axis] Other Postretirement Other Postretirement Benefits Plan [Member] Cash provided by Operating Activities Net Cash Provided by (Used in) Operating Activities 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). Equity Investments Equity Method Investments and Joint Ventures Disclosure [Text Block] Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Boswell Units 1 and 2 Net Plant and Equipment Boswell Units 1 and 2 Net Plant and Equipment [Member] Boswell Units 1 and 2 Net Plant and Equipment Other Other Accrued Liabilities, Current Corporate and Other Corporate, Non-Segment [Member] Amortization of Prior Service Credits Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Regulatory Liability [Domain] Regulatory Liability [Domain] Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] Line of credit draw outstanding Line of Credit, Current Depreciation and Amortization Depreciation, Depletion and Amortization Loss on Investments and Property, Plant and Equipment Gain (Loss) on Disposition of Other Assets Interest rate Debt Instrument, Interest Rate, Stated Percentage Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Regulatory Assets and Liabilities Schedule Of Regulatory Assets And Liabilities [Table Text Block] Schedule Of Regulatory Assets And Liabilities Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Total ALLETE Equity Equity, Attributable to Parent Consolidation Items [Axis] Consolidation Items [Axis] Gross unrecognized tax benefits that would favorably impact effective income tax rate Unrecognized Tax Benefits that Would Impact Effective Tax Rate Other Postretirement Benefit Plans Other Postretirement Benefit Plans Other Postretirement Benefit Plans Deferred Revaluation – Net of Federal Income Tax Benefit Effective Income Tax Rate Reconciliation, Deferred Revaluation – Net of Federal Income Tax Benefit Effective Income Tax Rate Reconciliation, Deferred Revaluation – Net of Federal Income Tax Benefit Extension period Line of Credit Facility, Extension Line of Credit Facility, Extension Asset Retirement Obligations Asset Retirement Obligation Costs [Member] Revision of Prior Period [Domain] Revision of Prior Period [Domain] Income Before Income Taxes Income Before Income Taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Fair Value Fair Value Measurement, Policy [Policy Text Block] Level 2 Fair Value, Inputs, Level 2 [Member] Long-term contract for purchase of electric power Long-Term Contract For Purchase Of Electric Power, Term Of Contract (Years) Term in years of long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. 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Adjustments to Reconcile Net Income to Cash provided by (used in) Operating Activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] All Trading Arrangements All Trading Arrangements [Member] All Adjustments to Compensation All Adjustments to Compensation [Member] Award Timing Disclosures [Line Items] Principal Principal [Abstract] Principal Compensation Amount Outstanding Recovery Compensation Amount Caddo Caddo [Member] Caddo Net Loss Attributable to Non-Controlling Interest Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Bad Debt Expense Accounts Receivable, Credit Loss Expense (Reversal) Deferred Income Tax Benefit Total Deferred Income Tax Expense (Benefit) Deferred Income Tax Expense (Benefit) Subsequent Event Type [Axis] Subsequent Event Type [Axis] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Surety Bonds Surety Bond [Member] Short-Term Debt Debt, Current Income Tax Expense Income Tax, Policy [Policy Text Block] Investment in ATC Equity Method Investments [Policy Text Block] Insider Trading Arrangements [Line Items] Amortization of the Remeasurement of Deferred Income Taxes Amortization From The Remeasurement Of Deferred Income Taxes For Equity Method Investments Amortization From The Remeasurement Of Deferred Income Taxes For Equity Method Investments Pension and Other Postretirement Benefit Plans [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Fuel Adjustment Clause Regulatory Clause Revenues, under-Recovered [Member] Square Butte Coal-Fired Unit Square Butte Coal-Fired Unit [Member] Square Butte Coal-fired Unit located near Center, North Dakota Non-Jurisdictional Land Sales Non-Jurisdictional Land Sales [Member] Non-Jurisdictional Land Sales Business Segments [Table] Schedule of Segment Reporting Information, by Segment [Table] Cash, Cash Equivalents and Restricted Cash Schedule Of Cash, Cash Equivalents And Restricted Cash [Table Text Block] Schedule of Cash, Cash Equivalents and Restricted Cash [Table Text Block] Entity Registrant Name Entity Registrant Name Customer Class [Axis] Customer Class [Axis] Customer Class [Axis] description of customer types or classes Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Award Timing Method Award Timing Method [Text Block] Redemption cost liability Accrual for Environmental Loss Contingencies Adjustment to Compensation, Amount Adjustment to Compensation Amount Other Current Liabilities Increase (Decrease) in Other Current Liabilities Non-Controlling Interest in Subsidiaries Equity, Attributable to Noncontrolling Interest Guarantor Obligations [Table] Schedule of Guarantor Obligations [Table] Document Period End Date Document Period End Date Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Customer Class [Domain] Customer Class [Domain] [Domain] for Customer Class [Axis] description of customer types or classes Adoption Date Trading Arrangement Adoption Date Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Recurring Fair Value Measures Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Corporate and Other Corporate and Other [Member] Repayments of Short-Term and Long-Term Debt Repayments of Long-Term Debt Finance Lease Liabilities Finance Lease, Liability, Noncurrent Entity Central Index Key Entity Central Index Key Liabilities Liabilities, Fair Value Disclosure [Abstract] Business Segments [Line Items] Segment Reporting Information [Line Items] Regulatory Differences – Excess Deferred Tax Effective Income Tax Rate Reconciliation, Regulatory Differences Regulatory Differences contributing to difference in effective tax rate to federal statutory rate. 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