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Property, Plant and Equipment [Abstract] Property, Plant and Equipment [Abstract] 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 Increase (Decrease) in Accounts Payable for Capital Additions to Property, Plant and Equipment Deferred Income Tax Expense (Benefit) [Abstract] Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract] Information for Pension Plans with an Accumulated Benefit Obligation in Excess of Plan Assets [Table Text Block] Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Table Text Block] First Mortgage Bonds - 4.95% Series Due 2044 [Member] ALLETE Bonds 4.95% Due March2044 [Member] ALLETE Bonds 4.95% Due March2044 [Member] Debt Instrument [Axis] Debt Instrument [Axis] Property, Plant and Equipment in Service Property, Plant and Equipment, Gross Dividends on Common Stock Common Stock Dividends Payments of Ordinary Dividends, Common Stock Square Butte [Member] Square Butte [Member] Square Butte [Member] ALLETE Clean Energy Other [Member] ALLETE Clean Energy Other [Member] ALLETE Clean Energy Other Revenue Recognized From Other Sources Immaterial For Disaggregation [Member] Property, Plant and Equipment, Additions Property, Plant and Equipment, Additions Inventories – Net [Abstract] Inventory, Net [Abstract] U.S. Large-cap [Member] U.S. Large-Cap [Member] Equity Securities, U.S. Large-Cap [Member] Debt Instrument, Basis Spread on Variable Rate Debt Instrument, Basis Spread on Variable Rate Regulated Operations [Member] Regulated Operations [Member] [Member] Operation of entities that are regulated by governmental organizations for example, but not limited to, local, state, county, country, or other regulatory organizations. 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2.50% Series Due 2030 ALLETE Bonds 2.50% Due August 2030 [Member] ALLETE Bonds 2.50% Due August 2030 Lease Contractual Term [Domain] Lease Contractual Term [Domain] Natural Gas-Fired [Member] Natural Gas Processing Plant [Member] Plan Name [Domain] Plan Name [Domain] Surety Bonds [Member] Surety Bond [Member] Balance, Equity Common Stock, Value, Outstanding Entity Address, State Entity Address, State or Province Employee Stock Purchase Plan (ESPP) [Member] Employee Stock [Member] Other Comprehensive Income (Loss) [Abstract] Other Comprehensive Income (Loss), Net of Tax [Abstract] Liabilities Recognized Asset Retirement Obligation, Liabilities Incurred Award Type [Axis] Award Type [Axis] Transaction Purchase Price Transaction Purchase Price Transaction Purchase Price Actuarial (Gain) Loss Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) 2026 Defined Benefit Plan, Expected Future Benefit Payment, Year Five Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax Operating Lease Liabilities, Current Less: Current Lease Obligations Operating Lease, Liability, Current Industrial [Member] Industrial [Member] Industrial Sales Channel [Member] Valuation and Qualifying Accounts and Reserves [Line Items] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] Increase (Decrease) in Tax Due to: [Abstract] Increase (Decrease) in Tax [Abstract] Increase (Decrease) in Tax [Abstract] First Mortgage Bonds - 4.39% Series Due 2044 [Member] ALLETE Bonds 4.39% Due September 2044 [Member] ALLETE Bonds 4.39% Due September 2044 [Member] Number of entities Number of entities Number of entities Solar Generation Solar Generation [Member] Solar Generation Other Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount Operating Expenses [Abstract] Costs and Expenses [Abstract] Wholesale Electric Contracts (Through 2029) Wholesale Electric Contracts (Through 2029) [Member] Wholesale Electric Contracts (Through 2029) Easements [Member] Easements [Member] Easements [Member] Property, Plant, and Equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] Long-Term Debt Net Long-Term Debt Long-Term Debt, Excluding Current Maturities Basin Power Sales Agreement (expires May 2028) [Member] Basin Power Sales Agreement (expires May 2028) [Member] Basin Power Sales Agreement (expires May 2028) [Member] Total Liabilities Liabilities Liabilities Operating Lease, Weighted Average Remaining Lease Term Operating Lease, Weighted Average Remaining Lease Term Stock-based Compensation [Line Items] Share-Based Compensation Expense [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Investing Activities Net Cash Provided by (Used in) Investing Activities [Abstract] Estimated Future Benefit Payments [Table Text Block] Schedule of Expected Benefit Payments [Table Text Block] 2021 Integrated Resource Plan [Member] 2021 Integrated Resource Plan [Member] 2021 Integrated Resource Plan Expected Additional Investment in 2022 Equity Method Investment, Expected Additional Investment Next Fiscal Year Additional investments expected to be made in the next fiscal year in an equity method investment. Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Fair Value Hierarchy and NAV [Domain] Total [Domain] Fair Value Hierarchy and NAV [Domain] Bank Lines of Credit [Member] Revolving Credit Facility [Member] Current Income Tax Expense [Abstract] Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Document Type Document Type Estimated Useful Lives Property, Plant and Equipment, Useful Life Unsecured Term Loan, Amount Unsecured Term Loan, Amount Unsecured Term Loan, Amount Assets [Abstract] Assets, Fair Value Disclosure [Abstract] As of January 1 As of December 31 Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Municipal Customers [Member] Municipal Customers [Member] Municipal Customers [Member] include cities, governments and other municipalities Investments [Abstract] Investments [Abstract] Deferred Income Tax Benefit Total Deferred Income Tax Expense (Benefit) Deferred Income Tax Expense (Benefit) Non-Current Assets Assets for Plan Benefits, Defined Benefit Plan Transmission [Axis] Transmission [Axis] Information about each transmission investment. More-Likely-Than-Not Percentage MoreLikelyThanNotDefined The percentage guideline to determine more-likely-than-not status Other Income (Expense) - Other [Abstract] Other Income (Expense) - Other [Abstract] Other Income (Expense) - Other [Abstract] Output Being Purchased - Electric Energy (MW) Long-Term Contract for Purchase of Electric Energy (MW) Long-Term Contract for Purchase of Electric Energy (MW) Superior, WI [Member] Superior, WI [Member] Superior, WI FERC-Approved Wholesale Rates [Member] FERC-Approved Wholesale Rates [Member] Wholesale rates approved by the Federal Energy Regulatory Commission (FERC). Long-Term Debt Equity Method Investment, Summarized Financial Information, Long-Term Debt Equity Method Investment, Summarized Financial Information, Long-Term Debt Net Identifiable Assets Acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Debt Disclosure [Abstract] Debt Disclosure [Abstract] Accounts Receivable [Policy Text Block] Accounts Receivable [Policy Text Block] Income Statement Location [Axis] Income Statement Location [Axis] Diamond Spring [Member] Diamond Spring [Member] Diamond Spring [Member] Defined Benefit Plan, Plan Assets, Contributions by Employer Employer Contribution Defined Benefit Plan, Plan Assets, Contributions by Employer Output Being Sold Electric - Capacity (MW) Long-term Contract for Sale of Electric Capacity (MW) Long-term Contract for Sale of Electric Capacity (MW) Non-Controlling Interest Details [Line Items] Non-Controlling Interest Details [Line Items] Non-Controlling Interest Details Long-Term Debt Due Within One Year Less: Due Within One Year Long-Term Debt, Current Maturities Cash provided by Financing Activities Net Cash Provided by (Used in) Financing Activities Production Tax Credits Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount Accounting Policies [Abstract] Non-Controlling Interest Details [Table] Non-Controlling Interest Details [Table] Non-Controlling Interest Details Fair Value of Plan Assets Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets ALLETE Equity [Abstract] Stockholders' Equity Attributable to Parent [Abstract] Customer [Axis] Customer [Axis] Document and Entity Information [Abstract] Document and Entity Information [Abstract] Document and Entity Information [Abstract] Private Equity [Member] Private Equity Funds [Member] Interest Cost Defined Benefit Plan, Interest Cost Unrealized Gain (Loss) on Securities, Income Tax Expense (Benefit) OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax Electric Rates [Member] Electric Rates [Member] Electric Rates [Member] Electric Rates [Member] Income Tax Expense [Table Text Block] Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Manitoba Hydro [Member] Manitoba Hydro [Member] Manitoba Hydro [Member] Leases Maturities [Abstract] Leases Maturities [Abstract] Leases Maturities [Abstract] Weighted-Average Period for Recognition (Years/Months) Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Financial Instruments [Table Text Block] Fair Value, by Balance Sheet Grouping [Table Text Block] Regulated Operations [Member] Regulated Operations [Member] Regulated Operations [Member] Employee Benefits and Compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation Entity Registrant Name Entity Registrant Name 2025 Defined Benefit Plan, Expected Future Benefit Payment, Year Four 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. Regulatory Assets for Benefit Obligations Deferred Tax Liabilities, Regulatory Assets for Benefit Obligations Deferred Tax Liabilities, Regulatory Assets for Benefit Obligations Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Minimum Annual Payments for Certain Long-Term Commitments [Line Items] Unrecorded Unconditional Purchase Obligation [Line Items] Benefits Paid Defined Benefit Plan, Benefit Obligation, Benefits Paid Component of Other Income (Expense) - Other [Axis] Component of Other Income (Expense) - Other [Axis] Component of Other Income (Expense) - Other [Axis] Pension and Other Postretirement Benefit Plans [Text Block] Retirement Benefits [Text Block] Sale of Wind Energy Facility [Member] Sale of Wind Energy Facility [Member] Sale of Wind Energy Facility [Member] Leases [Abstract] Leases [Abstract] Total Equity Balance, Beginning of Period Balance, Ending of Period Members' Equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest NOL Carryforwards Deferred Tax Assets, Operating Loss Carryforwards Schedule of Error Corrections and Prior Period Adjustments Schedule of Error Corrections and Prior Period Adjustments [Table Text Block] Principles of Consolidation [Policy Text Block] Consolidation, Policy [Policy Text Block] Basin Electric Power Cooperative [Member] Basin Electric Power Cooperative [Member] Basin Electric Power Cooperative Expected Output Entitlement (Percent) Minnesota Power Output Entitlement (Percent) Long-Term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased Minimum [Member] Minimum [Member] Environmental Matters [Table] Site Contingency [Table] Entity Emerging Growth Company Entity Emerging Growth Company Commercial [Member] Commercial [Member] Revenue Recognized From Commercial Customers Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Payment Arrangement, Amount Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-Based Payment Arrangement, Amount Valuation and Qualifying Accounts and Reserves [Table] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] CIP Consolidated Filing Member CIP Consolidated Filing Member [Member] CIP Consolidated Filing Member Investment, Name [Axis] Equity Method Investment [Axis] Investment, Name [Axis] Fair Value [Text Block] Fair Value Disclosures [Text Block] NOL Carryforwards, Valuation Allowance Operating Loss Carryforwards, Valuation Allowance 2026-01-01 2026-01-01 [Member] 2026-01-01 Trading Symbol Trading Symbol Entity File Number Entity File Number PPAs [Member] Power Purchase Agreement [Member] Power Purchase Agreement [Member] Accrued Interest Interest Payable, Current Regulatory Proceeding [Domain] Public Utilities, Regulatory Proceeding [Domain] Manufactured Gas Plant [Member] Manufactured Gas Plant [Member] Manufactured Gas Plant [Member] Manitoba Hydro PPA (expires May 2035) [Member] Manitoba Hydro PPA (expires 2035) [Member] Manitoba Hydro PPA (expires 2035) [Member] Revision of Prior Period - Adjusted Balance Revision of Prior Period - Adjusted Balance [Member] Revision of Prior Period - Adjusted Balance Net Loss Attributable to Non-Controlling Interest Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Subsequent Events [Policy Text Block] Subsequent Events, Policy [Policy Text Block] Derivatives [Policy Text Block] Derivatives, Policy [Policy Text Block] Granted Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Effective Tax Rate Effective Income Tax Rate Reconciliation, Percent Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Expected Employer Contributions in 2022 Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year Bonds Fair Value Disclosure, off-Balance-Sheet Risks, Face Amount, Liability Impairment Charge - After Tax Impairment Charge - After Tax Impairment Charge - After Tax Acquisitions [Text Block] Business Combination Disclosure [Text Block] Revision of Prior Period, Error Correction, Adjustment Revision of Prior Period, Error Correction, Adjustment [Member] Accounts Payable Increase (Decrease) in Accounts Payable Error Corrections and Prior Period Adjustments Restatement [Line Items] Error Corrections and Prior Period Adjustments Restatement [Line Items] Equity Method Investments and Joint Ventures [Abstract] Equity Method Investments and Joint Ventures [Abstract] Concentration Risk, Percentage Percent of Operating Revenue Concentration Risk, Percentage Fuel, Purchased Power and Gas - Utility Fuel, Purchased Power and Gas - Utility Fuel, Purchased Power and Gas - Utility Income Tax Expense [Text Block] Income Tax Disclosure [Text Block] Authorized Return on Equity Equity Method Investment, Approved Return on Common Equity The approved percentage return on common equity dedicated to the utility plant in the investee accounted for under the equity method of accounting. Annual Financing Payment Debt Instrument, Periodic Payment (Gain) / Loss on Investments and Property, Plant and Equipment Gain (Loss) on Disposition of Other Assets Credit Facility [Domain] Credit Facility [Domain] Public Utilities Reserve for Interim Rates (Recorded During Period) Public Utilities Reserve for Interim Rates (Recorded During Period) Public Utilities Reserve for Interim Rates (Recorded During Period) Jointly-Owned Facilities and Assets [Abstract] Jointly-Owned Facilities and Assets [Abstract] Jointly-Owned Facilities and Assets [Abstract] Basic Earnings Per Share of Common Stock Earnings Per Share Earnings Per Share, Basic Available-for-sale Securities, Debt Maturities, After Three Years Through Five Years, Fair Value 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). First Mortgage Bonds - 5.82% Series Due 2040 [Member] 5.82% Series Due 2040 [Member] First Mortgage Bonds, 5.82% Series Due 2040 [Member] Construction Work in Progress Construction in Progress, Gross Equity Investments [Table] Schedule of Equity Method Investments [Table] Awarded, Grant Date Fair Value Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Square Butte PPA [Member] Square Butte PPA (expires 2026) [Member] Square Butte PPA [Member] Long-term contract with Square Butte for the purchase of electric power. 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Changes in Operating Assets and Liabilities Increase (Decrease) in Operating Capital [Abstract] Regulatory Assets and Liabilities Currently Earning a Return Types of Net Regulatory Assets Earning Returns Notice Required to Terminate (Years) Length of Notice Required to Terminate (Years) The length of notice required to terminate a contract (in years). Contract Serving Requirement Contract Serving Requirement Contract Serving Requirement Change in Cash, Cash Equivalents and Restricted Cash Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect Wholesale and Retail Contra AFUDC [Member] Wholesale and Retail Contra AFUDC [Member] Wholesale and Retail Contra AFUDC [Member] First Mortgage Bonds - 6.00% Series Due 2040 [Member] 6.00% Series Due 2040 [Member] First Mortgage Bonds, 6.00% Series Due 2040 [Member] Class of Stock [Axis] Class of Stock [Axis] Cost Recovery Riders [Member] Cost Recovery Riders [Member] Cost Recovery Riders [Member] Long-Term Debt Maturing Thereafter Long-Term Debt, Maturity, after Year Five Income Taxes [Policy Text Block] Income Tax, Policy [Policy Text Block] Available-for-Sale Securities [Policy Text Block] Marketable Securities, Policy [Policy Text Block] Document [Domain] Document [Domain] North Dakota Investment Tax Credits [Member] North Dakota Investment Tax Credits Subject to Refund [Member] North Dakota Investment Tax Credits Subject to Refund [Member] Invest Direct, Equity Stock Issued During Period, Value, Dividend Reinvestment Plan Unsecured Term Loan Variable Rate Due 2023 Unsecured Term Loan Variable Rate Due 2023 [Member] Unsecured Term Loan Variable Rate Due 2023 Total Assets Acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets Current Assets [Abstract] Assets, Current [Abstract] Wind Turbine Generators [Member] Wind Turbine Generators [Member] Wind Turbine Generators [Member] Unbilled Unbilled Receivables, Current Contract Asset - Noncurrent Contract with Customer, Asset, after Allowance for Credit Loss, Noncurrent Retained Earnings Retained Earnings (Accumulated Deficit) Effect of Plan Curtailment Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement Estimated Capital Expenditures, ALLETE Portion Estimated Capital Expenditures, ALLETE Portion Estimated Capital Expenditures, ALLETE Portion Unearned Grant Award Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Unearned Grant Award Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Shares of original grant unearned (not paid out), a reduction to non-vested shares balance, similar to a forfeiture. Recurring Fair Value Measures [Member] Fair Value, Recurring [Member] Approved Return on Common Equity Public Utilities, Approved Return on Equity, Percentage Document Fiscal Year Focus Document Fiscal Year Focus Defined Benefit Plan, Plan Assets, Category [Domain] Defined Benefit Plan, Plan Assets, Category [Domain] Operating Activities Net Cash Provided by (Used in) Operating Activities [Abstract] 2020 Minnesota General Rate Review [Member] 2020 Minnesota General Rate Review [Member] 2020 Minnesota General Rate Review [Member] Consolidation, Eliminations [Member] Consolidation, Eliminations [Member] Power Sales Agreement - Capacity [Axis] Long-term Contract for Sale of Capacity [Axis] Long-term Contract for Sale of Capacity [Axis] Fair Value Hierarchy and NAV [Axis] Defined Benefit Plan, Fair Value of Plan Assets by Measurement [Axis] Fair Value Hierarchy and NAV [Axis] Camp Ripley Financing [Member] Camp Ripley Financing [Member] Camp Ripley Financing [Member] Unrecognized Tax Benefits, Penalties Unrecognized Tax Benefits, Income Tax Penalties Expense Loss Contingencies [Table] Loss Contingencies [Table] Oliver Wind [Member] Oliver Wind [Member] Oliver Wind [Member] Total Current Income Tax Expense Current Income Tax Expense (Benefit) Long-term Contracts for Sale of Electric Power [Domain] Power Sales Agreement - Energy and Capacity [Domain] Long-term Contracts for Sale of Electric Power [Domain] Long-term Contracts for Sale of Electric Power [Domain] Impairment of Long-Lived Assets [Policy Text Block] Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Power Purchase Agreement - Energy [Axis] Long-term Contract for Purchase of Energy [Axis] Long-term Contract for Purchase of Energy [Axis] Deferred Income Tax Liabilities [Abstract] Deferred Tax Liabilities, Gross [Abstract] Regulatory Asset [Axis] Regulatory Asset [Axis] Equity Method Investment, Nonconsolidated Investee [Axis] Equity Method Investment, Nonconsolidated Investee [Axis] Accounts Receivable [Abstract] Accounts Receivable, after Allowance for Credit Loss, Current [Abstract] Coal Combustion Residuals [Member] Coal Combustion Residuals [Member] Coal Combustion Residuals [Member] Share-Based Compensation - Equity Share-Based Compensation - Equity Share-Based Compensation - Equity Inventories Increase (Decrease) in Inventories First Mortgage Bonds - 5.10% Series Due 2025 [Member] 5.10% Series Due 2025 [Member] First Mortgage Bonds, 5.10% Series Due 2025 [Member] ATC [Member] ATC [Member] ATC [Member] Document and Entity Information [Table] Document Information [Table] Common Stock, Shares Outstanding Balance, Shares Common Stock, Shares, Outstanding Goodwill Goodwill Length of Notice Required to Terminate Contract Length of Notice Required to Terminate Contract Length of Notice Required to Terminate Contract Property, Plant and Equipment, Type [Axis] Long-Lived Tangible Asset [Axis] Actual Return on Plan Assets Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) Short-Term Debt - Unamortized Debt Issuance Costs Debt Issuance Costs, Current, Net 2022 Wisconsin General Rate Case 2022 Wisconsin General Rate Case [Member] 2022 Wisconsin General Rate Case Income Tax Benefit Total Income Tax Expense (Benefit) Income Tax Expense (Benefit) Income Tax Expense (Benefit) Geographical [Domain] Geographical [Domain] Deferred Income Tax Asset Valuation Allowance Deferred Tax Assets, Valuation Allowance Cash Equivalents Other Restricted Assets, Noncurrent Deferred Income Taxes Deferred Income Tax Liabilities, Net Entity Public Float Entity Public Float Balance Sheet Location [Domain] Balance Sheet Location [Domain] First Mortgage Bonds - 3.69% Series Due 2024 [Member] ALLETE Bonds 3.69% Due March2024 [Member] ALLETE Bonds 3.69% Due March2024 [Member] Cost of Sales - Non-utility Cost of Goods and Services Sold Beginning Obligation Ending Obligation Asset Retirement Obligation Accumulated Depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Minnkota Power [Member] Minnkota Power [Member] Minnkota Power [Member] PPA Counterparty Annual Debt Service through 2026 Long-Term Contract for Purchase of Electric Power, Annual Minimum Debt Service Payment Required Loss Contingencies [Line Items] Loss Contingencies [Line Items] Unamortized Investment Tax Credits Accumulated Deferred Investment Tax Credit 2022 Defined Benefit Plan, Expected Future Benefit Payment, Year One Common Stock Without Par Value, 80.0 Shares Authorized, 57.2 and 53.2 Shares Issued and Outstanding Common Stock, Value, Issued Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Guarantee Entity and Type [Axis] Guarantee Entity and Type [Axis] Guarantee Entity and Type [Axis] Additions, Other Charges SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Other Account Current Liabilities Liability, Defined Benefit Plan, Current Accumulated Benefit Obligation Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation Basin Electric Cooperative PSA June 2023 - May 2025 [Member] Basin Electric Cooperative PSA June 2023 - May 2025 [Member] Basin Electric Cooperative PSA June 2023 - May 2025 [Member] Business Acquisition, Pro Forma Information, Description Business Acquisition, Pro Forma Information, Description Cash and Cash Equivalents Cash, Cash Equivalents and Restricted Cash on the Consolidated Statement of Cash Flows Cash, Cash Equivalents and Restricted Cash on the Consolidated Statement of Cash Flows Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents Investment Tax Credit Amortization Deferred Other Tax Expense (Benefit) Estimated Investment Amount Estimated Investment Amount Estimated Investment Amount Current Liabilities [Abstract] Liabilities, Current [Abstract] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Regulatory Matters [Table] Public Utilities General Disclosures [Table] Customer Deposits Contract with Customer, Liability, Current First Mortgage Bonds - 2.79% Series Due 2031 2.79% Series Due 2031 [Member] 2.79% Series Due 2031 Other Postretirement Benefit Plans Other Postretirement Benefit Plans Other Postretirement Benefit Plans Excise Taxes [Policy Text Block] Excise Tax Policy [Policy Text Block] Policy regarding the collection and recording of excise taxes. Retirement Plan Type [Domain] Retirement Plan Type [Domain] Income Statement Location [Domain] Income Statement Location [Domain] Amendment Flag Amendment Flag Residual Value of Leased Asset Residual Value of Leased Asset Minnesota Power Output Entitlement (MW) Long-Term Contract for Purchase of Electric Power, Share of Plant Output Purchased (MW) Long-Term Contract for Purchase of Electric Power, Share of Plant Output Purchased Long-Term Finance Receivables [Policy Text Block] Financing Receivable, Held-for-investment [Policy Text Block] Operating Lease, Cost Operating Lease, Cost Resource Package [Member] Resource Package [Member] Resource Package [Member] Environmental Remediation Contingency [Domain] Environmental Remediation Contingency [Domain] SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] Total Other Comprehensive Income (Loss) Other Comprehensive Income (Loss), Net of Tax Output Being Sold Electric - Energy and Capacity (MW) Long-term Contract for Sale of Electric Energy and Capacity (MW) Long-term Contract for Sale of Electric Energy and Capacity (MW) Total Liabilities Assumed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities Purchase Option Purchase Option, Asset Purchase option to acquire an asset. 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Common Stock, Shares Authorized Common Stock, Shares Authorized Guarantor Obligations [Table] Schedule of Guarantor Obligations [Table] First Mortgage Bonds - 3.30% Series Due 2028 [Member] ALLETE Bonds 3.30% Due October2028 [Member] ALLETE Bonds 3.30% Due October2028 [Member] Distribution [Member] Electric Distribution [Member] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Maximum [Member] Maximum [Member] Non-Controlling Interest in Subsidiaries [Policy Text Block] Consolidation, Subsidiaries or Other Investments, Consolidated Entities, Policy [Policy Text Block] Selected Quarterly Financial Information [Abstract] Selected Quarterly Financial Information [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Cash and Cash Equivalents Cash and Cash Equivalents, at Carrying Value Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] ALLETE Properties Real Estate Investments, Net Public Utilities, Interim Rate Increase (Decrease), Percentage Public Utilities, Interim Rate Increase (Decrease), Percentage Business Acquisition [Line Items] Business Acquisition [Line Items] Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Measurement Frequency [Domain] Measurement Frequency [Domain] Common Stock and Earnings Per Share [Text Block] Stockholders' Equity Note Disclosure [Text Block] Components of Net Periodic Cost [Table Text Block] Schedule of Net Benefit Costs [Table Text Block] Lines of Credit [Table] Line of Credit Facility [Table] Payments for Purchase of Available-for-sale Securities Payments to Acquire Debt Securities, Available-for-Sale Employer Contributions to Defined Benefit Pension Plans - Common Stock Shares Employer Contributions to Pension - Shares Stock Issued During Period, Shares, Employee Benefit Plan Gross Unrecognized Income Tax Benefits [Abstract] Income Tax Uncertainties [Abstract] Supplemental Statement of Cash Flow Information [Table Text Block] Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Corporate & Other - Other [Member] Corporate & Other - Other [Member] Revenue Recognized by Corporate & Other From Other Sources Immaterial for Disaggregation Actual Plan Asset Allocations Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage Share-Based Compensation - Shares Share-Based Compensation - Shares Share-Based Compensation - Shares Income Tax Benefit Share-Based Payment Arrangement, Expense, Tax Benefit Variable Interest Entities [Policy Text Block] Consolidation, Variable Interest Entity, Policy [Policy Text Block] Title of 12(b) Security Title of 12(b) Security Pension and Other Postretirement Benefit Plan Disclosures [Table] Pension and Other Postretirement Benefit Plans Recurring Fair Value Measures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Fixed Income [Member] Fixed Income Securities [Member] Other Income (Expense) - Other [Table] Other Income (Expense) - Other [Table] Other Income (Expense) - Other [Table] Large Power Customers [Member] Large Power Customers [Member] Large Power Customer [Member] Large Power Customer [Member] Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Purchase, Sale, and Settlement Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Purchase, Sale, and Settlement 2018 Wisconsin General Rate Case [Member] 2018 Wisconsin General Rate Case [Member] 2018 retail rate increase request filed with the PSCW [Member] Weighted Average Assumptions Used to Determine Benefit Obligation and Net Periodic Benefit Costs [Table Text Block] Defined Benefit Plan, Assumptions [Table Text Block] Employer Contributions to Defined Benefit Pension Plans - Cash Defined Benefit Plan, Plan Assets, Cash Contributions by Employer Defined Benefit Plan, Plan Assets, Cash Contributions by Employer Segment Reporting Disclosure [Text Block] Segment Reporting Disclosure [Text Block] Commitments Contingencies and Guarantees Commitments Contingencies and Guarantees [Text Block] Equity Method Investment, Nonconsolidated Investee [Domain] Equity Method Investment, Nonconsolidated Investee [Domain] Other Receivables Other Receivables Previously Reported Previously Reported [Member] Net Deferred Income Taxes Deferred Tax Liabilities, Net Liabilities and Equity [Abstract] Liabilities and Equity [Abstract] Liabilities and Equity [Abstract] Recurring Fair Value Measurements [Table] Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis [Table] Fair Value, Recurring and Nonrecurring [Table] Business Combination, Reason for Business Combination Business Combination, Reason for Business Combination Inventories – Net Total Inventories – Net Inventory, Net Silver Bay Power [Member] Silver Bay Power [Member] Silver Bay Power [Member] Long-term Contracts for Sale of Electric Power [Axis] Power Sales Agreement - Energy and Capacity [Axis] Long-term Contracts for Sale of Electric Power [Axis] Long-term Contracts for Sale of Electric Power [Axis] Accounts Payable Accounts Payable, Current Anticipated Generating Capacity to be Purchased (MW) Anticipated Generating Output to be Purchased (MW) Anticipated Generating Output to be Purchased (MW) Income Tax Authority [Axis] Income Tax Authority [Axis] Other Other Accrued Liabilities, Noncurrent WPPI Energy Ownership % Jointly-Owned Electric Facility Percentage Not Owned Jointly-Owned Electric Facility Percentage Not Owned Proceeds from Issuance of Common Stock Proceeds from Issuance of Common Stock Basic (Shares) Average Common Shares Weighted Average Number of Shares Outstanding, Basic Caddo [Member] Caddo [Member] Caddo Ownership Percentage Equity Method Investment, Ownership Percentage Equity Method Investment, Ownership Percentage Revolving Credit Facility Variable Rate Due 2025 Revolving Credit Facility Variable Rate Due 2025 [Member] Revolving Credit Facility Variable Rate Due 2025 Change in Plan Assets [Roll Forward] Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Requested Average Rate Increase Public Utilities, Requested Rate Increase (Decrease), Percentage Plan Asset Target Allocations Defined Benefit Plan, Plan Assets, Target Allocation, Percentage Irrevocable Grantor Trust [Member] Trust for Benefit of Employees [Member] Trust for Benefit of Employees [Member] Industrial Development Variable Rate Demand Refunding Revenue Bonds Series 2006, Due 2025 [Member] Industrial Development Variable Rate Demand Refunding Revenue Bonds Series 2006 Due 2025 [Member] Industrial Development Variable Rate Demand Refunding Revenue Bonds Series 2006 Due 2025 [Member] Trend Rate Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year Restricted Cash included in Prepayments and Other Restricted Cash, Current First Mortgage Bonds - 6.02% Series Due 2023 [Member] 6.02% Series Due 2023 [Member] First Mortgage Bonds, 6.02% Series Due 2023 [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Minimum Annual Payments for Certain Long-Term Commitments [Axis] Unrecorded Unconditional Purchase Obligation by Category of Item Purchased [Axis] Annual Debt Service Period [Domain] Annual Debt Service Period [Domain] [Domain] for Annual Debt Service Period [Axis] Percentage of Total Regulated Utility kWh Sales Percentage of Total Regulated Utility kWh Sales Percentage of Total Regulated Utility kWh Sales Short-Term Debt - Outstanding Debt, Current Recurring Fair Value Measures - Activity in Level 3 [Table Text Block] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Leases [Policy Text Block] Lessee, Leases [Policy Text Block] Capital Purchase Obligations [Member] Capital Addition Purchase Commitments [Member] Level 3 [Member] Fair Value, Inputs, Level 3 [Member] Assets, Noncurrent Assets, Noncurrent Available-for-sale – Corporate and Governmental Debt Securities Debt Securities, Available-for-Sale, Noncurrent Employee Stock and Incentive Plans [Text Block] Share-Based Payment Arrangement [Text Block] Share-Based Compensation Expense [Table Text Block] Share-Based Payment Arrangement, Cost by Plan [Table Text Block] Square Butte [Member] Square Butte Coal-fired Unit [Member] Square Butte Coal-fired Unit [Member] Square Butte Coal-fired Unit located near Center, North Dakota Contracts with Customers – Non-utility Unregulated Operating Revenue Jointly-Owned Facilities and Projects [Domain] Jointly Owned Utility Plant [Domain] Alternative Programs [Member] Alternative Programs [Member] Alternative Programs Sales Channel [Member] Customer Class [Axis] Customer Class [Axis] Customer Class [Axis] description of customer types or classes Non-Controlling Interest in Subsidiaries [Member] Noncontrolling Interest [Member] Basin [Member] Basin [Member] Basin [Member] Retail Electric Service [Member] Retail Electric Service [Member] Retail Electric Service [Member] Deferred Tax Assets and Liabilities [Table Text Block] Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Silver Bay Power Self-Generation [Member] Silver Bay Power Coal, Liquid and Gaseous Fuels-fired Units [Member] Silver Bay Power Coal, Liquid and Gaseous Fuels-fired Units [Member] Related Party [Axis] Related Party [Axis] Guarantor Obligations by Nature [Axis] Guarantor Obligations, Nature [Axis] Earnings Per Share - Diluted [Abstract] Earnings Per Share, Diluted [Abstract] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Summary of Common Stock [Table Text Block] Schedule of Common Stock Outstanding Roll Forward [Table Text Block] Jointly-Owned Facilities and Assets [Axis] Jointly Owned Utility Plant [Axis] Acquisitions of Subsidiaries – Net of Cash and Restricted Cash Acquired Payments to Acquire Businesses, Net of Cash Acquired Level 2 [Member] Fair Value, Inputs, Level 2 [Member] Business Acquisition, Goodwill, Expected Tax Deductible Amount Business Acquisition, Goodwill, Expected Tax Deductible Amount Unamortized Discount and Premium on Debt [Policy Text Block] Debt, Policy [Policy Text Block] Current Fiscal Year End Date Current Fiscal Year End Date Other Current Assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other Approved Equity Ratio Public Utilities, Approved Equity Capital Structure, Percentage Accretion Asset Retirement Obligation, Accretion Expense Activity in Level 3 [Roll Forward] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Minimum Annual Payments for Certain Long-Term Commitments [Domain] Unconditional Purchase Obligation, Category of Goods or Services Acquired [Domain] Other Power Supplier Customers [Member] Other Power Supplier Customers [Member] Other Power Supplier Customers Participant Contributions Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant Regulatory Liabilities Deferred Tax Assets, Regulatory Liabilities Deferred Tax Assets, Regulatory Liabilities Minimum Payments in 2026 Unrecorded Unconditional Purchase Obligation, to be Paid, Year Four Concentration Risk Type [Axis] Concentration Risk Type [Axis] Total Current Liabilities Liabilities, Current Liabilities, Current Accounts Receivable [Table Text Block] Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Unrecognized Postretirement Health and Life Costs [Table Text Block] Schedule of Net Periodic Benefit Cost Not yet Recognized [Table Text Block] Customer Concentration Risk [Member] Customer Concentration Risk [Member] Oliver Wind II PPA [Member] Oliver Wind II PPA [Member] Long-term contract with an affiliate of NextEra Energy, Inc. for the purchase of electric power. Unrecognized Tax Benefits that Would Impact Effective Tax Rate Unrecognized Tax Benefits that Would Impact Effective Tax Rate Revenue, Remaining Performance Obligation, Amount Revenue, Remaining Performance Obligation, Amount Business Combinations, Fair Value Adjustments Business Combinations, Fair Value Adjustments Business Combinations, Fair Value Adjustments Jointly-Owned Electricity Generation Plant [Member] Jointly Owned Electricity Generation Plant [Member] Other Income (Expense) [Abstract] Nonoperating Income (Expense) [Abstract] Accounts Receivable, Allowance Accounts Receivable, Allowance Accounts and Other Receivables, Net, Current Generating Capacity Counterparty Owned (MW) Generating Capacity Counterparty Owned (MW) Generating Capacity Counterparty Owned (MW) Generating Capacity Counterparty Owned (MW) SWL&P First Mortgage Bonds 4.15% Series Due 2028 [Member] SWL&P First Mortgage Bonds 4.15% Series Due 2028 [Member] SWL&P First Mortgage Bonds 4.15% Series Due 2028 [Member] Income Tax Authority [Domain] Income Tax Authority [Domain] Other Financing Activities Proceeds from (Payments for) Other Financing Activities Power Purchase Agreement - Capacity [Axis] Long-term Contract for Purchase of Electric Capacity [Axis] Long-term Contract for Purchase of Electric Capacity [Axis] Other Non-Current Assets [Abstract] Other Assets, Noncurrent [Abstract] Nobles 2 PPA [Member] Tenaska PPA [Member] Tenaska PPA [Member] ALLETE Bonds 4.54% Due August 2032 ALLETE Bonds 4.54% Due August 2032 [Member] ALLETE Bonds 4.54% Due August 2032 South Shore Energy South Shore Energy [Member] South Shore Energy Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Credit Facility [Axis] Credit Facility [Axis] Unrealized Gain (Loss) on Securities - Net of Income Tax Expense (Benefit) of $(0.2), $(0.1) and $0.1 Unrealized Gain (Loss) on Debt Securities OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract] Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents [Abstract] Equity [Abstract] Equity [Abstract] Awarded Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Entity Tax Identification Number Entity Tax Identification Number 2023-01-01 [Member] 2023-01-01 [Member] 2023-01-01 [Member] ESPP Discount Share-Based Compensation Arrangement by Share-Based Payment Award, Discount from Market Price, Purchase Date CIP Consolidated Filing [Member] CIP Consolidated Filing [Member] CIP Consolidated Filing [Member] AFUDC - Equity [Member] AFUDC - Equity [Member] AFUDC - Equity [Member] Capitalized Contract Cost [Table] Capitalized Contract Cost [Table] ALLETE South Wind [Member] ALLETE South Wind [Member] ALLETE South Wind Minnesota Power Ownership % Jointly Owned Utility Plant, Proportionate Ownership Share Calpine Corporation PPA [Member] Calpine Corporation PPA [Member] Calpine Corporation PPA Jointly-Owned Facilities and Assets [Table] Jointly Owned Utility Plant Interests [Table] Equity Issuance Program, Shares Stock Issued During Period, Shares, Other Estimated Obligation Guarantor Obligations, Maximum Exposure, Undiscounted Other [Member] Other Regulatory Assets (Liabilities) [Member] Wholesale Electric Service [Member] Wholesale Electric Service [Member] Wholesale Electric Service [Member] Net Loss Net (Gain) Loss Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense [Table Text Block] Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] State Income Taxes – Net of Federal Income Tax Benefit Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Property Related Deferred Tax Assets, Property, Plant and Equipment Entity Central Index Key Entity Central Index Key Auditor Information [Abstract] Auditor Information [Abstract] Auditor Information First Mortgage Bonds - 4.47% Series Due 2049 [Member] ALLETE Bonds 4.47% Due March 2049 [Member] ALLETE Bonds 4.47% Due March 2049 [Member] Stock-Based Compensation [Table] Share-Based Compensation Expense [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Business Combination, Consideration Transferred Business Combination, Consideration Transferred Entity [Domain] Entity [Domain] City Area Code City Area Code Assets [Abstract] Assets [Abstract] Assets [Abstract] Industrial Customers [Member] Industrial Customers [Member] Industrial Customers Pension and Other Postretirement Benefit Plans [Policy Text Block] Pension and Other Postretirement Plans, Policy [Policy Text Block] Draws Outstanding Line of Credit, Current Minimum Annual Payments for Certain Long-Term Commitments [Table] Unrecorded Unconditional Purchase Obligation [Table] Equity Issuance Program Shares Authorized Equity Issuance Program Shares Authorized Aggregate number of shares, without par value, authorized to be issued under the distribution agreement with KCCI (equity issuance program/PIE). Debt Instrument, Redemption, Period [Axis] Debt Instrument, Redemption, Period [Axis] Renewable Generation [Member] Renewable Generation [Member] Renewable Generation Approximate Refund for Reversale of FERC ROE Order, ALLETE's Proportionate Share Approximate Refund for Reversal of FERC ROE Order, ALLETE's Proportionate Share Approximate Refund for Reversal of FERC ROE Order, ALLETE's Proportionate Share Capitalized Contract Cost [Line Items] Capitalized Contract Cost [Line Items] Long-Term Debt Maturing in 2022 Long-Term Debt, Maturity, Year One Noncash Investing and Financing Activities [Abstract] Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Share-Based and ESOP Compensation Expense Share-Based Payment Arrangement, Noncash Expense Payments for Equity Investments Cash Investments Payments to Acquire Equity Method Investments Regulatory Asset Regulatory Asset WPPI Energy [Member] WPPI Energy [Member] WPPI Energy [Member] Common Stock Issued Stock Issued During Period, Value, Other Variable Rate [Axis] Variable Rate [Axis] Other Non-Current Liabilities Total Other Non-Current Liabilities Other Liabilities, Noncurrent Equity Earnings ALLETE's Equity in Net Income Income (Loss) from Equity Method Investments Additions to Property, Plant and Equipment Payments to Acquire Property, Plant, and Equipment Regulatory Matters [Text Block] Public Utilities Disclosure [Text Block] Ownership Percentage of Benefited Property Community Development District Obligation, Ownership of Property Benefited Ownership percentage of property benefitied by a real estate development project funded by municipal capital improvement revenue and special assessment bonds. Weighted Average Weighted Average [Member] Obligation, Beginning of Year Obligation, End of Year Defined Benefit Plan, Benefit Obligation Reconciliation of Basic and Diluted Earnings Per Share [Table Text Block] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Power Sales Agreement - Capacity [Domain] Long-term Contract for Sale of Capacity [Domain] [Domain] for Long-term Contract for Sale of Capacity [Axis] Approximate Refund for Reversal of FERC ROE Order Approximate Refund for Reversal of FERC ROE Order Approximate Refund for Reversal of FERC ROE Order Minnesota Cost Recovery Riders [Member] Current Cost Recovery Rider [Member] Current Cost Recovery Rider [Member] Conservation Improvement Program Goal, In 2 Years Conservation Improvement Program Goal, In 2 Years Conservation Improvement Program Goal, In 2 Years Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense [Abstract] Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract] Customer [Domain] Customer [Domain] Postretirement Health and Life [Member] Other Postretirement Benefits Plan [Member] Other Postretirement Benefits Plan [Member] First Mortgage Bonds - 4.07% Series Due 2048 [Member] ALLETE Bonds 4.07% Due April 2048 [Member] ALLETE Bonds 4.07% Due April 2048 [Member] 2016 Minnesota General Rate Review 2016 Minnesota General Rate Review [Member] 2016 Minnesota General Rate Review Non-controlling interest Effective Income Tax Rate Reconciliation, Noncontrolling Interest Income (Loss), Amount Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Consolidated Statement of Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Rate of Compensation Increase Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase Total Lease Payments Due Lessee, Operating Lease, Liability, to be Paid Net Income Net Income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Discount Rate - Input for Goodwill Analysis Discount Rate - Input for Goodwill Analysis Discount Rate - Input for Goodwill Analysis Town Center District Capital Improvement Bonds [Member] Town Center Community Development District [Member] Community development district obligations for Town Center District. FERC Authorized Return on Equity Including Incentive Adder FERC Authorized Return on Equity, Including Incentive Adder FERC Authorized Return on Equity, Including Incentive Adder Retail Customers [Member] Retail Customers [Member] Retail Customers [Member] include residential customers, commercial customers and industrial customers. Transmission Services - Utility Transmission Services - Utility Transmission Services - Utility Entity Address, Postal Zip Code Entity Address, Postal Zip Code Component of Other Income (Expense) - Other [Domain] Component of Other Income (Expense) - Other [Domain] [Domain] for Component of Other Income (Expense) - Other [Axis] First Mortgage Bonds - 3.30% Series Due 2050 ALLETE Bonds 3.30% Due August 2050 [Member] ALLETE Bonds 3.30% Due August 2050 Great River Energy [Member] Great River Energy [Member] Great River Energy [Member] Gross Unrecognized Income Tax Benefits [Roll Forward] Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Long-Term Debt Maturing in 2023 Long-Term Debt, Maturity, Year Two Adjustment of Redeemable Non-Controlling Interest Noncontrolling Interest, Change in Redemption Value Basis Point Incentive adder Basis Point Incentive adder Basis Point Incentive adder Business Combinations Policy Business Combinations Policy [Policy Text Block] Plan Amendments Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment Invest Direct, Shares Stock Issued During Period, Shares, Dividend Reinvestment Plan Redeemable Non-Controlling Interest Redeemable Non-Controlling Interest Redeemable Non-Controlling Interest Other [Member] Other [Member] Regulated Operations Other Revenue Recognized From Other Sources Immaterial For Disaggregation Maximum Borrowing Capacity Line of Credit Facility, Maximum Borrowing Capacity Income Taxes [Abstract] Income Tax Disclosure [Abstract] Property-Related Deferred Tax Liabilities, Property, Plant and Equipment Deductions from Reserves SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction Long-term Contract for Purchase of Electric Power [Domain] Long-Term Contract for Purchase of Electric Power [Domain] Generating Capacity Subject to Tax Equity Financing Generating Capacity Subject to Tax Equity Financing Generating Capacity Subject to Tax Equity Financing Revenue, Performance Obligation, Description of Payment Terms Revenue, Performance Obligation, Description of Payment Terms First Mortgage Bonds - 4.90% Series Due 2025 [Member] 4.90% Series Due 2025 [Member] First Mortgage Bonds, 4.90% Series Due 2025 [Member] Expected Period for Costs of Compliance Expected Period for Costs of Compliance Expected Period for Costs of Compliance Fuel Adjustment Clause 2022 Fuel Adjustment Clause 2022 [Member] Fuel Adjustment Clause 2022. Related to the 2022 Fuel Adjustment Clause year. Other Income (Expense) - Other [Table Text Block] Schedule of Other Nonoperating Income (Expense) [Table Text Block] Other Income (Expense) - Other [Line Items] Other Income (Expense) - Other [Line Items] [Line Items] for Other Income (Expense) - Other [Table] Amortization of Other Intangible Assets and Other Assets Other Depreciation and Amortization Other Investing Activities Payments for (Proceeds from) Other Investing Activities Statistical Measurement [Domain] Statistical Measurement [Domain] Contract Term (Years) 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. Approved Rate Increase - Amount Public Utilities, Approved Rate Increase (Decrease), Amount Cash Contributions to Defined Benefit Pension Plans Payment for Pension Benefits Share-based Payment Arrangement [Abstract] Share-Based Payment Arrangement [Abstract] Net Pension Cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Vehicles and Equipment [Member] Vehicles and Equipment [Member] Vehicles and Equipment [Member] Other Current Liabilities Increase (Decrease) in Other Current Liabilities First Mortgage Bonds - 4.21% Series Due 2043 [Member] ALLETE Bonds 4.21% Due October2043 [Member] ALLETE Bonds 4.21% Due October2043 [Member] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Net Income Attributable to ALLETE Net Income Attributable to ALLETE Net Income Attributable to ALLETE Net Income (Loss) Attributable to Parent Other Income (Expense) - Other [Member] Other Income (Expense) - Other [Member] Other Income (Expense) - Other [Member] Contracts with Customers – Utility Regulated Operating Revenue Amortization of Prior Service Cost Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Subsequent Event Type [Axis] Subsequent Event Type [Axis] Sale of Wind Energy Facility Sale of Wind Energy Facility Sale of Wind Energy Facility Rate of Compensation Increase Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase Billed Accounts Receivable, before Allowance for Credit Loss, Current Long-term Contract [Member] Long-term Contract [Member] Long-term Contract Revenue Stream [Member] Minnkota Sales Agreement [Member] Minnkota Sales Agreement [Member] Minnkota Sales Agreement [Member] Revisions in Estimated Cash Flows Asset Retirement Obligation, Revision of Estimate Environmental Remediation Contingency [Axis] Environmental Remediation Contingency [Axis] Total Fair Value of Assets Assets, Fair Value Disclosure Nobles 2 [Member] Nobles 2 [Member] Nobles 2 [Member] PSA Liability PSA Liability [Member] PSA Liability Regulatory Assets and Liabilities Disclosure [Abstract] Regulatory Assets and Liabilities Disclosure [Abstract] First Mortgage Bonds - 3.74% Series Due 2029 [Member] ALLETE Bonds 3.74% Due September 2029 [Member] ALLETE Bonds 3.74% Due September 2029 [Member] FERC Proposed Reduction to Incentive Adder FERC Proposed Reduction to Incentive Adder FERC Proposed Reduction to Incentive Adder Plan Name [Axis] Plan Name [Axis] PPACA Income Tax Deferral [Member] 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). Lines of Credit [Abstract] Line of Credit Facility [Abstract] Generating Capacity Under Construction (MW) Generating Capacity Under Construction (MW) Generating Capacity Under Construction (MW) Number of Operating Segments Number of Operating Segments Regulated Operations [Abstract] Regulated Operations [Abstract] Boswell Unit 4 [Member] Boswell Unit 4 [Member] Boswell Unit 4 [Member] Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Level 1 [Member] Fair Value, Inputs, Level 1 [Member] Estimated Future Benefit Payments [Abstract] Defined Benefit Plan, Expected Future Benefit Payment [Abstract] Other Current Liabilities [Table Text Block] Other Current Liabilities [Table Text Block] State Capital Loss State Capital Loss State Capital Loss Prior Service Credit Prior Service Credit Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax Rate Type [Axis] Rate Type [Axis] Rate Type [Axis] including categories like electric rates, natural gas rates, water rates, etc. Accounts Receivable Increase (Decrease) in Accounts and Other Receivables Sale of Renewable Development Projects Sale of Renewable Development Projects [Member] Sale of Renewable Development Projects Cost of Purchased Power Utilities Operating Expense, Purchased Power under Long-Term Contracts Public Utility - Additional Rider Revenue Public Utility - Additional Rider Revenue Public Utility - Additional Rider Revenue Cash provided by Operating Activities Net Cash Provided by (Used in) Operating Activities Long-term PSA [Member] Long-term PSA [Member] Revenue Recognized From Long-term PSAs Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual Restricted Stock Units [Table Text Block] Share-Based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block] Financing Renewal Term (Years) Debt Instrument, Renewal Term Renewal term for a debt instrument disclosing for what period of time after maturity the instrument may be extended. Accounts Receivables [Abstract] Receivables [Abstract] Equity Investments [Line Items] Schedule of Equity Method Investments [Line Items] Document Annual Report Document Annual Report Legal Entity [Axis] Legal Entity [Axis] Regulatory Assets and Liabilities [Policy Text Block] Public Utilities, Policy [Policy Text Block] Power Purchase Agreements [Axis] Power Purchase Agreement - Energy and Capacity [Axis] Long-Term Contract for Purchase of Electric Power [Axis] Geographical [Axis] Geographical [Axis] Proposed Ongoing Customer Rate Increase Proposed Ongoing Customer Rate Increase Proposed Ongoing Customer Rate Increase Business Acquisition, Percentage of Voting Interests Acquired Business Acquisition, Percentage of Voting Interests Acquired Defined Benefit Pension and Other Postretirement Benefit Plans Non-Current Liabilities Liability, Defined Benefit Plan, Noncurrent Common Stock Issued Stock Issued During Period, Value, New Issues Financial Covenants [Abstract] Debt Instruments [Abstract] Property, Plant and Equipment and Estimated Useful Lives of Property, Plant and Equipment [Table Text Block] Property, Plant and Equipment [Table Text Block] Other Non-Current Liabilities Equity Method Investment, Summarized Financial Information, Other Non-Current Liabilities Equity Method Investment, Summarized Financial Information, Other Non-Current Liabilities Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] 2024 Defined Benefit Plan, Expected Future Benefit Payment, Year Three Materials and Supplies Inventory, Supplies, Net of Reserves Generating Facility Unit Name [Domain] Generating Facility Unit Name [Domain] [Domain] for Name of generating unit or facility [Axis] Accounts Receivable Business Combination, Acquired Receivable, Fair Value Terminal Growth Rate - Input for Goodwill Analysis Terminal Growth Rate - Input for Goodwill Analysis Terminal Growth Rate - Input for Goodwill Analysis Business Segments [Axis] Segments [Axis] Short-Term and Long-Term Debt [Text Block] Debt Disclosure [Text Block] Product and Service [Domain] Product and Service [Domain] Schedule of Regulatory Assets and Liabilities (Table Text Block) Schedule of Regulatory Assets and Liabilities [Text Block] Income Taxes [Member] Deferred Income Tax Charge [Member] Entity Shell Company Entity Shell Company Reduction for Tax Positions Related to Prior Years Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions Plan Asset Actual and Target Allocations [Table Text Block] Schedule of Allocation of Plan Assets [Table Text Block] Concentration Risk [Table] Concentration Risk [Table] Taxes Other than Income Taxes Taxes, Other 2023 Lessee, Operating Lease, Liability, to be Paid, Year One NOL and Tax Credit Carryforwards [Line Items] NOL and Tax Credit Carryforwards [Line Items] NOL and Tax Credit Carryforwards [Line Items] Long-Term Debt Maturing in 2024 Long-Term Debt, Maturity, Year Three Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] Consolidation Items [Domain] Consolidation Items [Domain] Subsequent Event [Member] Subsequent Event [Member] Consolidated Operating Revenue [Member] Revenue Benchmark [Member] Document Period End Date Document Period End Date Equity Issuance Program Shares Available for Issuance Equity Issuance Program Shares Available for Issuance The number of shares of common stock that remain available for issuance under the equity issuance program (KCCI distribution agreement). Boswell 1 & 2 [Member] Boswell 1 & 2 [Member] Boswell 1 & 2 [Member] Amortization of Prior Service Cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax Total Assets Assets Assets 2025-01-01 [Member] 2025-01-01 [Member] 2025-01-01 Average Shares of Common Stock and Per Share Data [Abstract] Earnings Per Share [Abstract] Public Utilities - Reserve for Interim Rate Refund Public Utilities - Reserve for Interim Rate Refund Public Utilities - Reserve for Interim Rate Refund PIE Shares PIE Shares [Member] PIE Shares Performance Shares [Member] Performance Shares [Member] Granted, Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Total Grant Date Fair Value The total grant date fair value of equity-based awards other than options, granted during the period. Requested Return on Equity Public Utilities, Requested Return on Equity, Percentage PPA Counterparty Total Debt Outstanding Long-Term Contract for Purchase of Electric Power, Amount of Long-Term Debt or Lease Obligation Outstanding First Mortgage Bonds - 4.85% Series Due 2021 [Member] 4.85% Series Due 2021 [Member] First Mortgage Bonds, 4.85% Series Due 2021 [Member] Environmental Matters [Line Items] Site Contingency [Line Items] 2027 Lessee, Operating Lease, Liability, to be Paid, Year Five Long-term Investments Long-Term Investments Short-Term and Long-Term Debt - Fair Value Long-Term Debt, Fair Value Income Before Non-Controlling Interest and Income Taxes Income Before Non-Controlling Interest and Income Taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest U.S. Small-cap [Member] U.S. Small Cap [Member] Equity Securities, U.S. Small Cap [Member] Business Segments [Domain] Segments [Domain] Power Purchase Agreement - Capacity [Domain] Long-term Contract for Purchase of Electric Capacity [Domain] [Domain] for Long-term Contract for Purchase of Electric Capacity [Axis] Manufactured Gas Plant - Current Manufactured Gas Plant - Current Manufactured Gas Plant - Current Other Deferred Tax Liabilities, Other Plant in Service Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service Regulatory Asset [Domain] Total Regulatory Assets [Domain] Regulatory Asset [Domain] Deferred Compensation Deferred Compensation Liability, Classified, Noncurrent Cash and Cash Equivalents [Policy Text Block] Cash and Cash Equivalents, Policy [Policy Text Block] Total Comprehensive Income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Award Type [Domain] Award Type [Domain] Approximate Pre-Tax Reserve for Deferred Residential Customer Interim Rates Approximate Pre-Tax Reserve for Deferred Residential Customer Interim Rates Approximate Pre-Tax Reserve for Deferred Residential Customer Interim Rates Other Non-Current Assets [Table Text Block] Schedule of Other Assets, Noncurrent [Table Text Block] Stock Issued During Period, Shares, New Issues Stock Issued During Period, Shares, New Issues Cost Recovery Riders [Member] Regulatory Clause Revenues, under-Recovered [Member] 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. Regulatory Agency [Axis] Regulatory Agency [Axis] Unrecognized Tax Benefits [Policy Text Block] Income Tax Uncertainties, Policy [Policy Text Block] 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. Goodwill and Intangible Assets, Goodwill, Policy Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Inventory Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory Entity Address, City Entity Address, City or Town U.S. Mid-cap Growth [Member] U.S. Mid-Cap Growth [Member] Equity Securities, U.S. Mid-Cap Growth [Member] Gain on Sale After Tax Gain on Sale After Tax Gain on Sale After Tax Provision (Payments) for Interim Rate Refund Provision (Payments) for Interim Rate Refund Provision (Payments) for Interim Rate Refund Contract with Customer, Sales Channel [Axis] Contract with Customer, Sales Channel [Axis] Years 2027 - 2031 Defined Benefit Plan, Expected Future Benefit Payment, after Year Five for Next Five Years Non-Controlling Interest in Subsidiaries Stockholders' Equity Attributable to Noncontrolling Interest Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Partnership Basis Differences Deferred Tax Liabilty, Partnership Basis Differences Deferred Tax Liability, Partnership Basis Differences Unrecognized Tax Benefits, Accrued Interest Unrecognized Tax Benefits, Interest on Income Taxes Accrued PPA Annual Debt Service Obligation (Percentage) Long-term Contract for Purchase of Electric Power, Annual Minimum Debt Service Payment Required, Obligation (Percentage) Long-term Contract for Purchase of Electric Power, Annual Minimum Debt Service Payment Required, Obligation (Percentage) Largest Customer [Member] Largest Customer [Member] Largest Customer [Member] Oconto Electric Cooperative Power Sales Agreement [Member] Oconto Electric Cooperative Power Sales Agreement [Member] Oconto Electric Cooperative Power Sales Agreement Actual Indebtedness to Total Capitalization Ratio Debt Instrument, Actual Indebtedness to Total Capital Ratio Actual indebtedness to total capital ratio required to be maintained by most restrictive financial covenant. Asset Retirement Obligation Asset Retirement Obligations, Noncurrent Accumulated Contributions in Excess of Net Periodic Benefit Cost (Prepaid Pension Asset) Accumulated Net Periodic Benefit Cost in Excess of Contributions Accumulated Contributions in Excess of Net Periodic Benefit Cost (Prepaid Pension Asset) Accumulated Contributions in Excess of Net Periodic Benefit Cost (Prepaid Pension Asset) Unamortized Debt Issuance Costs Debt Issuance Costs, Net Nemadji Trail Energy Center [Member] Nemadji Trail Energy Center [Member] Nemadji Trail Energy Center [Member] Business Segments [Table] Schedule of Segment Reporting Information, by Segment [Table] Auditor Name Auditor Name Bond Interest Rate Community Development District Obligation, Bond Interest Rate Interest rate of capital improvement revenue and special assessment bonds used to fund real estate development projects. Annual Additional Revenue Generated from Requested Final Rate Increase Public Utilities, Requested Rate Increase (Decrease), Amount Pension [Member] Pension Plan [Member] Pension Plan [Member] 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. NOL Carryforwards Operating Loss Carryforwards Real Estate [Member] Real Estate [Member] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Restricted Stock Units [Member] Restricted Stock Units (RSUs) [Member] Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held 4.54% Series Due 2032 4.54% Series Due 2032 [Member] 4.54% Series Due 2032 Generating Capacity (MW) Anticipated Additional Generating Capacity (MW) Anticipated Additional Generating Capacity (MW) Reclassification of Redeemable Non-Controlling Interest to Current Liabilities Non-Cash Reclassification of Redeemable Non-Controlling Interest to Current Liabilities Non-Cash Reclassification of Redeemable Non-Controlling Interest to Current Liabilities Customer Refund Liability, Current Customer Refund Liability, Current Total Operating Revenue Revenue Operating Revenue Revenues Great River Energy Power Sales Agreement (expires May 2025) Great River Energy Power Sales Agreement (expires May 2025) [Member] Great River Energy Power Sales Agreement (expires May 2025) Regulatory Asset, Current Regulatory Asset, Current Taconite Harbor [Member] Taconite Harbor [Member] Taconite Harbor Energy Center Other Power Suppliers [Member] Other Power Suppliers [Member] Other Power Suppliers Sales Channel [Member] State Deferred State and Local Income Tax Expense (Benefit) Armenia Mountain Senior Secured Notes 3.26% Due 2024 [Member] Armenia Mountain Senior Secured Notes 3.26% Due 2024 [Member] Armenia Mountain Senior Secured Notes 3.26% Due 2024 [Member] Cash Paid During the Period for Interest – Net of Amounts Capitalized Interest Paid, Excluding Capitalized Interest, Operating Activities Bond Term (Years) Community Development District Obligation, Bond Term, in Years Term (in years) of capital improvement revenue and special assessment bonds used to fund real estate development projects. 2025 Lessee, Operating Lease, Liability, to be Paid, Year Three Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] First Mortgage Bonds - 3.20% Series Due 2026 [Member] ALLETE Bonds 3.20% Due July2026 [Member] ALLETE Bonds 3.20% Due July2026 [Member] Inventories [Policy Text Block] Inventory, Policy [Policy Text Block] ALLETE, Inc. [Member] ALLETE, Inc. [Member] -- None. No documentation exists for this element. -- Long-Term Service Agreements [Member] Other Purchase Obligations [Member] Other Purchase Obligations [Member] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Counterparty Name [Domain] Counterparty Name [Domain] Total ALLETE Equity Stockholders' Equity Attributable to Parent Tax Credit Carryforwards Tax Credit Carryforward, Amount Power Purchase Agreement - Energy [Domain] Long-term Contract for Purchase of Energy [Domain] [Domain] for Long-term Contract for Purchase of Energy [Axis] Forfeited Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value New Energy New Energy [Member] New Energy Equity Lines of Credit [Line Items] Line of Credit Facility [Line Items] Tax Credit Carryforwards Deferred Tax Assets, Tax Credit Carryforwards Other Deferred Tax Assets, Other Land and Other [Member] Land and Other [Member] Land and Other [Member] Revenue Collection Period Following the Annual Period it is Recognized Revenue Collection Period Following the Annual Period it is Recognized Revenue Collection Period Following the Annual Period it is Recognized Capitalized Contract Cost, Amortization Capitalized Contract Cost, Amortization Energy Generation Owned (MW) Generating Capacity Owned (MW) Generating Capacity Owned (MW) Asset Retirement Obligations [Policy Text Block] Asset Retirement Obligation [Policy Text Block] Document and Entity Information, Document [Axis] Document Information, Document [Axis] Deferred Interim Rates Deferred Interim Rates Deferred Interim Rates First Mortgage Bonds - 2.50% Due August 2030 [Member] ALLETE Bonds 4.08% Due March 2029 [Member] ALLETE Bonds 4.08% Due March 2029 [Member] Other Other Assets, Miscellaneous, Noncurrent Boswell Unit 3 [Member] Boswell Unit 3 [Member] Boswell Unit 3 Long-Term Debt Maturing in 2026 Long-Term Debt, Maturity, Year Five Proceeds from Sale of Available-for-sale Securities Proceeds from Sale of Debt Securities, Available-for-Sale Retained Earnings [Member] Retained Earnings [Member] Business Segments [Line Items] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Reclassification of Redeemable Non-Controlling Interest to Current Liabilities Reclassification of Redeemable Non-Controlling Interest to Current Liabilities Reclassification of Redeemable Non-Controlling Interest to Current Liabilities Capital Cost Spent to Date Capital Cost Spent to Date Capital cost spent to date for project. Common Stock [Member] Common Stock [Member] Oliver Wind I PPA [Member] Oliver Wind I PPA [Member] Long-term contract with an affiliate of NextEra Energy, Inc. for the purchase of electric power. Transmission Assets [Member] CapX2020 [Member] CapX2020 (all projects) [Member] Number of Reportable Segments Number of Reportable Segments Lease, Cost [Table Text Block] Lease, Cost [Table Text Block] Shares Available for Issuance Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant Total Regulatory Liabilities [Domain] Regulatory Liability [Domain] Revenue Recognition [Policy Text Block] Revenue [Policy Text Block] Fuel Energy Related Inventory, Coal Consolidated Statement of Equity [Table] Statement [Table] NOL and Tax Credit Carryforwards [Table Text Block] Summary of Tax Credit Carryforwards [Table Text Block] Awarded Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Performance Shares [Table Text Block] Schedule of Nonvested Performance-Based Units Activity [Table Text Block] Regulatory Assets Deferred Tax Liabilities, Regulatory Assets Operating Lease Liabilities, Non-Current Long-term Lease Obligations Operating Lease, Liability, Noncurrent Statistical Measurement [Axis] Statistical Measurement [Axis] Nontrade Receivables, Current Nontrade Receivables, Current Fair Value Transfers [Policy Text Block] Fair Value Transfer, Policy [Policy Text Block] Tenaska [Member] Nobles 2 [Member] Tenaska [Member] Tenaska Energy, Inc. and Tenaska Energy Holdings, LLC [Member] Liabilities Settled Asset Retirement Obligation, Liabilities Settled Jointly-Owned Facilities and Assets [Line Items] Jointly Owned Utility Plant Interests [Line Items] Total Accounts Receivable Accounts Receivable, after Allowance for Credit Loss, Current Rate Information by Type [Domain] Rate Information by Type [Domain] Rate Information by Type [Domain] Equity Components [Axis] Equity Components [Axis] Equity Components [Axis] Amounts Recognized in Consolidated Balance Sheet [Table Text Block] Schedule of Amounts Recognized in Balance Sheet [Table Text Block] Proceeds from Non-Controlling Interest in Subsidiaries - Net of Issuance Costs Proceeds from Non-Controlling Interest - Net of Issuance Costs Proceeds from Noncontrolling Interests Accumulated Depreciation Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation Generation Type [Axis] Generation Type [Axis] Generation Type [Axis] Business Segments [Policy Text Block] Segment Reporting, Policy [Policy Text Block] BNI Energy [Member] BNI Energy [Member] BNI Energy [Member] Available-for-sale Securities, Debt Maturities, After Five Years, Fair Value 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). Revision of Prior Period [Domain] Revision of Prior Period [Domain] Regulatory Agency [Domain] Regulatory Agency [Domain] Consolidated Statement of Equity [Line Items] Statement [Line Items] Income from Equity Investments – Net of Dividends Income (Loss) from Equity Method Investments, Net of Dividends or Distributions As of January 1 As of December 31 Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Total Other Expense Nonoperating Income (Expense) Variable Rate [Domain] Variable Rate [Domain] 2022 Minnesota General Rate Review 2022 Minnesota General Rate Review [Member] 2022 Minnesota General Rate Review Operating Lease, Right-of-Use Asset Operating Lease, Right-of-Use Asset Accumulated Other Comprehensive Loss [Member] AOCI Attributable to Parent [Member] Equity Method Investment, Summarized Financial Information [Abstract] Equity Method Investment, Summarized Financial Information [Abstract] Auditor Firm ID Auditor Firm ID Document Transition Report Document Transition Report 2023 Defined Benefit Plan, Expected Future Benefit Payment, Year Two Local Phone Number Local Phone Number Reclassification of Property, Plant and Equipment to Inventory Reclassification of Property, Plant and Equipment to Inventory Reclassification of Property, Plant and Equipment to Inventory Operating Income Operating Income Operating Income (Loss) Prior Service Credit Arising During the Period Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Reclassification Adjustment, before Tax Prepayments and Other Increase (Decrease) in Prepaid Expense and Other Assets State [Member] State and Local Jurisdiction [Member] AFUDC – Equity AFUDC–Equity Increase (Decrease) in Allowance for Equity Funds Used During Construction ALLETE Senior Unsecured Notes 3.11% Due 2027 [Member] ALLETE Senior Unsecured Notes 3.11% Due 2027 [Member] ALLETE Senior Unsecured Notes 3.11% Due 2027 [Member] Annual Assessment Community Development District Obligation, Annual Assessment Amount of annual assessments based on ownership percentage of benefited property related to real estate development projects funded by municipal capital improvement revenue and special assessment bonds. Depreciation [Policy Text Block] Depreciation, Depletion, and Amortization [Policy Text Block] Total Fair Value of Liabilities Liabilities, Fair Value Disclosure Amortization of Loss Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax Regulated Utility - Interim Rate Refund Regulated Utility - Interim Rate Refund Regulated Utility - Interim Rate Refund Guarantee Entity and Type [Domain] Guarantee Entity and Type [Domain] [Domain] for Guarantee Entity and Type [Axis] Estimated Capital Expenditures, Including Past Expenditures Estimated Capital Expenditures, Including Past Expenditures The estimated amount of certain capital expenditures related to environmental compliance, regulatory matters, or other commitments and/or contingencies. This estimate includes expenditures expected in future periods and expenditures made through the end of the current period. Property, Plant and Equipment [Policy Text Block] Property, Plant and Equipment, Policy [Policy Text Block] 2026 Lessee, Operating Lease, Liability, to be Paid, Year Four Income Statement Data [Abstract] Income Statement [Abstract] Federal Deferred Federal Income Tax Expense (Benefit) Impairment of Long-Lived Assets Held-for-use Impairment, Long-Lived Asset, Held-for-Use Document Fiscal Period Focus Document Fiscal Period Focus Estimated Minimum Annual Payments for Certain Long-Term Commitments [Table Text Block] Unrecorded Unconditional Purchase Obligations Disclosure [Table Text Block] Earnings Per Share - Basic [Abstract] Earnings Per Share, Basic [Abstract] Unsecured Term Loan Variable Rate Due 2022 Unsecured Term Loan Variable Rate Due 2022 [Member] Unsecured Term Loan Variable Rate Due 2022 Restricted Cash included in Other Non-Current Assets Restricted Cash, Noncurrent Restricted Cash, Noncurrent ALLETE's Investment in ATC [Roll Forward] ALLETE's Investment in ATC [Roll Forward] ALLETE's Investment in ATC [Roll Forward] Diluted (Shares) Average Common Shares Weighted Average Number of Shares Outstanding, Diluted Guarantor Obligations [Line Items] Guarantor Obligations [Line Items] Inventories – Net [Table Text Block] Schedule of Inventory, Current [Table Text Block] Jointly-Owned Facilities and Assets [Table Text Block] Schedule of Jointly Owned Utility Plants [Table Text Block] Regulatory Assets Non-Current Regulatory Assets Regulatory Asset, Noncurrent Long-Term Debt due Within One Year Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Long-Term Debt Income Tax Expense [Abstract] Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] Available-for-sale – Equity Securities Equity Securities, FV-NI, Noncurrent Operating and Maintenance Other General and Administrative Expense Generating Facility Axis [Axis] Generating Facility [Axis] Name of generating unit or facility ICFR Auditor Attestation Flag ICFR Auditor Attestation Flag Current Regulatory Liability Regulatory Liability, Current Interest and Investment Earnings [Member] Interest and Investment Earnings [Member] Interest and Investment Earnings [Member] Current Liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities February Unsecured Term Loan Terminated in April 2022 February Unsecured Term Loan Terminated in April 2022 [Member] February Unsecured Term Loan Terminated in April 2022 Granted Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Recurring Fair Value Measures [Table Text Block] Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Capitalized Contract Cost [Domain] Capitalized Contract Cost [Domain] Power Sales Agreements Power Purchase Agreements, Deferred Tax Asset Power Purchase Agreements, Deferred Tax Asset Defined Benefit Plan - Amendments Defined Benefit Plan, Changes in Benefit Obligation and Plan Assets, Description SWL&P First Mortgage Bonds 4.14% Series Due 2048 [Member] SWL&P First Mortgage Bonds 4.14% Series Due 2048 [Member] SWL&P First Mortgage Bonds 4.14% Series Due 2048 [Member] Net Loss Attributable to Non-Controlling Interest Net Income (Loss) Attributable to Noncontrolling Interest Commitments, Guarantees and Contingencies [Text Block] Commitments and Contingencies Disclosure [Text Block] Proceeds from Issuance of Short-Term and Long-Term Debt Proceeds from Issuance of Long-Term Debt Generation [Member] Electricity Generation Plant, Non-Nuclear [Member] Equity Investments [Table Text Block] Equity Method Investments [Table Text Block] Common Stock, Shares Issued Common Stock, Shares, Issued Concentration Risk [Line Items] Concentration Risk [Line Items] Equity Investments Equity Investment Beginning Balance Equity Investment Ending Balance Equity Method Investments Administrative Law Judge Recommended Refund Administrative Law Judge Recommended Refund Administrative Law Judge Recommended Refund 2022 Wisconsin General Rate Review 2022 Wisconsin General Rate Review [Member] 2022 Wisconsin General Rate Review Other Expense Equity Method Investment, Summarized Financial Information, Other Expense The amount of other expense reported by an equity method investment of the entity. 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 Effective Income Tax Rate Reconciliation, Deferred Revaluation - Net of Federal Income Tax Benefit Business Combination, Acquisition Related Costs Business Combination, Acquisition Related Costs Long-Term Debt Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-Term Debt Recurring Fair Value Measures [Line Items] Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Cash used in Investing Activities Net Cash Provided by (Used in) Investing Activities Deferred Tax Liabilities - Deferred Gain Deferred Tax Liabilities - Deferred Gain Deferred Tax Liabilities - Deferred Gain Environmental Remediation Liability Environmental Remediation Liability Environmental Remediation Liability Requested Equity Ratio Public Utilities, Requested Equity Capital Structure, Percentage Federal [Member] Internal Revenue Service (IRS) [Member] Employee Stock Purchase Plan, Equity Stock Issued During Period, Value, Employee Stock Purchase Plan Corporate and Other [Member] Corporate and Other [Member] Total Comprehensive Income Attributable to ALLETE Comprehensive Income Attributable to ALLETE Comprehensive Income (Loss), Net of Tax, Attributable to Parent Employee Stock Ownership Plan [Abstract] Share-Based Payment Arrangement, Disclosure [Abstract] Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of Segment Reporting Information, by Segment [Table Text Block] Defined Benefit Pension and Other Postretirement Benefit Plans, Income Tax Expense (Benefit) Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax Entity Current Reporting Status Entity Current Reporting Status Asset Retirement Obligation [Member] Asset Retirement Obligation Costs [Member] Other Total Other Current Liabilities Other Liabilities, Current Debt Instrument [Abstract] Long-Term Debt, Fiscal Year Maturity [Abstract] Obligation and Funded Status [Table Text Block] Schedule of Net Funded Status [Table Text Block] Glen Ullin Energy Center [Member] Glen Ullin Energy Center [Member] Glen Ullin Energy Center [Member] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Environmental Liabilities [Policy Text Block] Environmental Costs, Policy [Policy Text Block] Contract with Customer, Duration [Axis] Contract with Customer, Duration [Axis] Statutory Federal Income Tax Rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Transmission [Member] Electric Transmission [Member] Long-term Contract with Customer [Member] Long-Term Contract with Customer [Member] Additions, Charged to Income SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense Employee Stock Purchase Plan, Shares Stock Issued During Period, Shares, Employee Stock Purchase Plans Schedule of Recognized Identified Assets Acquired and Liabilities Assumed Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Recognition of Regulatory Outcomes Policy Recognition of Regulatory Outcomes Policy [Policy Text Block] Recognition of Regulatory Outcomes Policy. Policy for timing of when regulatory outcomes are recognized in the financial statements of the issuer. Asset Retirement Obligation [Roll Forward] Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] Power Purchase Agreements [Line Items] Long-Term Contract for Purchase of Electric Power [Line Items] Summary of Common Stock [Table] Schedule of Stock by Class [Table] Deferred Income Tax Assets and Liabilities [Abstract] Components of Deferred Tax Assets and Liabilities [Abstract] First Mortgage Bonds - 5.99% Series Due 2027 [Member] 5.99% Series Due 2027 [Member] First Mortgage Bonds, 5.99% Series Due 2027 [Member] Financial Statement Preparation [Policy Text Block] Basis of Accounting, Policy [Policy Text Block] Liabilities [Abstract] Liabilities [Abstract] Property, Plant and Equipment – Net Property, Plant and Equipment – Net Property, Plant and Equipment, Net Operating Revenue [Abstract] Regulated Operating Revenue [Abstract] Quarterly Financial Data (Unaudited) [Text Block] Quarterly Financial Information [Text Block] Minimum Payments in 2023 Unrecorded Unconditional Purchase Obligation, to be Paid, Year One Effective income Tax Rate Reconciliation - Investment Tax Credits Effective income Tax Rate Reconciliation - Investment Tax Credits Effective income Tax Rate Reconciliation - Investment Tax Credits Changes in Regulatory and Other Non-Current Assets Increase (Decrease) in Other Noncurrent Assets Net Book Value Public Utilities, Property, Plant and Equipment, Net Debt Instrument, Redemption, Period [Domain] Debt Instrument, Redemption, Period [Domain] Forfeited Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period Total Long-Term Debt Long-Term Debt Other Total Other Income (Expense) - Other Other Nonoperating Income (Expense) First Mortgage Bonds - 3.40% Series Due 2022 [Member] ALLETE Bonds 3.40% Due July2022 [Member] ALLETE Bonds 3.40% Due July2022 [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Operations and Significant Accounting Policies [Text Block] Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Tax Credit Carryforwards, Valuation Allowance Tax Credit Carryforward, Valuation Allowance Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Fuel Adjustment Clause Changes in Fuel Adjustment Clause Regulatory Asset and Liability Changes in Fuel Adjustment Clause Regulatory Asset and Liability Customer Type [Domain] Customer Type [Domain] Customer Type [Domain] Year Ultimate Trend Rate Effective Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Income (Loss), Net of Tax Federal Capital Loss Federal Capital Loss Federal Capital Loss Expected Long-Term Return on Plan Assets Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-Term Rate of Return on Plan Assets Plan Curtailments Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment Transmission [Member] Jointly Owned Electricity Transmission and Distribution System [Member] Total Current Assets Total Current Assets Assets, Current Accrued Taxes Taxes Payable, Current International [Member] International [Member] Equity Securities, International [Member] Cash Paid (Received) for Income Taxes Income Taxes Paid, Net NOL and Tax Credit Carryforwards [Table] NOL and Tax Credit Carryforwards [Table] NOL and Tax Credit Carryforwards [Table] Entity Small Business Entity Small Business Contract with Customer, Duration [Domain] Contract with Customer, Duration [Domain] Dividends Per Share of Common Stock Common Stock, Dividends, Per Share, Declared Minimum Payments Thereafter Unrecorded Unconditional Purchase Obligation, to be Paid, after Year Five Distributions to Non-Controlling Interest Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Recurring Fair Value Measures [Table Text Block] Fair Value, Assets Measured on Recurring Basis [Table Text Block] Regulatory Liabilities Non-Current Regulatory Liabilities Regulatory Liability, Noncurrent Asset Retirement Obligations [Table Text Block] Schedule of Change in Asset Retirement Obligation [Table Text Block] Unrecognized Compensation Cost Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Valuation and Qualifying Accounts and Reserves [Roll Forward] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] Property, Plant and Equipment [Text Block] Property, Plant and Equipment Disclosure [Text Block] Regulatory Matters [Line Items] Public Utilities, General Disclosures [Line Items] Property, Plant and Equipment, Type [Domain] Long-Lived Tangible Asset [Domain] SWL&P [Member] SWL&P [Member] Superior, Water, Light and Power [Member] Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities [Table Text Block] Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block] ALLETE Clean Energy [Member] ALLETE Clean Energy [Member] ALLETE Clean Energy [Member] Other Non-Current Liabilities [Table Text Block] Other Noncurrent Liabilities [Table Text Block] Approximate Reduction in Pretax Income for FERC Proposal to Limit Incentive adder, ALLETE's Proportionate Share Approximate Reduction in Pretax Income for FERC Proposal to Limit Incentive adder, ALLETE's Proportionate Share Approximate Reduction in Pretax Income for FERC Proposal to Limit Incentive adder, ALLETE's Proportionate Share First Mortgage Bonds - 5.05% Series Due 2044 [Member] ALLETE Bonds 5.05% Due July2044 [Member] ALLETE Bonds 5.05% Due July2044 [Member] Distributed Earnings Proceeds from Equity Method Investment, Distribution Transmission Formula Rates [Member] Transmission Formula Rates [Member] Transmission Formula Rates Total Operating Expenses Costs and Expenses Annual Debt Service Period [Axis] Annual Debt Service Period [Axis] Annual Debt Service Period [Axis] Jointly-Owned Facilities and Assets [Text Block] Jointly-Owned Electric Facility [Text Block] Jointly-Owned Electric Facility [Text Block] Debt Instrument [Line Items] Debt Instrument [Line Items] Business Combination and Asset Acquisition [Abstract] Common Stock [Abstract] Common Stock, Number of Shares, Par Value and Other Disclosure [Abstract] Error Corrections and Prior Period Adjustments, Description Error Corrections and Prior Period Adjustments, Description Summary of Common Stock [Line Items] Class of Stock [Line Items] Operating Lease, Liability Total Lease Obligations Operating Lease, Liability Cash, Cash Equivalents and Restricted Cash [Table Text Block] Schedule of Cash, Cash Equivalents and Restricted Cash [Table Text Block] Schedule of Cash, Cash Equivalents and Restricted Cash [Table Text Block] Balance at Beginning of Period Balance at End of Period SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount Accounting for Stock-Based Compensation [Policy Text Block] Share-Based Payment Arrangement [Policy Text Block] Ultimate Trend Rate Defined Benefit Plan, Ultimate Health Care Cost Trend Rate Mutual Funds [Member] Fixed Income Funds [Member] Generation Type [Domain] Generation Type [Domain] [Domain] for Generation Type [Axis] Benefits Paid Defined Benefit Plan, Plan Assets, Benefits Paid South Peak [Member] South Peak [Member] South Peak [Member] Purchase Price Accounting - After Tax Purchase Price Accounting - After Tax Purchase Price Accounting - After Tax Deferred Income Tax Assets [Abstract] Deferred Tax Assets, Net of Valuation Allowance [Abstract] Defined Benefit Pension and Other Postretirement Benefit Plans [Member] Pension and Other Postretirement Plans Costs [Member] Pension and Other Postretirement Plans Costs [Member] Proceeds from Issuance of First Mortgage Bond Proceeds from Issuance of First Mortgage Bond Transmission [Domain] Transmission [Domain] Name of transmission investment. Comprehensive Income [Abstract] Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] BNI Energy Reclamation Liability [Member] BNI Coal Reclamation Liability [Member] Reclamation liability for closing costs associated with BNI Coal mine and mine facilities. Long-Term Debt Maturing in 2025 Long-Term Debt, Maturity, Year Four Auditor Location Auditor Location Entity Filer Category Entity Filer Category Equity [Abstract] Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Executive Long-Term Incentive Compensation Plan [Member] Executive Plan [Member] Stock based, long-term incentive compensation, Executive Plan [Member] Health Care Trend Rates [Abstract] Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract] Federal Current Federal Tax Expense (Benefit) First Mortgage Bonds - 4.08% Series Due 2042 [Member] ALLETE Bonds 4.08% Due July2042 [Member] ALLETE Bonds 4.08% Due July2042 [Member] Commission Approved Refund Commission Approved Refund Commission Approved Refund Liabilities [Abstract] Liabilities, Fair Value Disclosure [Abstract] Share-Based Compensation Expense Share-Based Payment Arrangement, Expense Commitments, Guarantees and Contingencies (Note 9) Commitments and Contingencies Security Exchange Name Security Exchange Name Finance Receivables – Long-Term [Member] SEC Schedule, 12-09, Allowance, Loss on Finance Receivable [Member] Other Liabilities [Abstract] Other Liabilities Disclosure [Abstract] Fair Value of Financial Instruments [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Quarterly Financial Data (Unaudited) [Table Text Block] Quarterly Financial Information [Table Text Block] Standby Letters of Credit Letters of Credit Outstanding, Amount Other No-Current Liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other Revenue from Contract with Customer, Excluding Assessed Tax Revenue from Contract with Customer, Excluding Assessed Tax Public Utilities, Interim Rate Increase (Decrease), Amount Public Utilities, Interim Rate Increase (Decrease), Amount First Mortgage Bonds - 3.02% Series Due 2021 [Member] ALLETE Bonds 3.02% Due September 2021 [Member] ALLETE Bonds 3.02% Due September 2021 [Member] Construction of Wind Energy Facilities Other Inventory, Gross Regulatory Liabilities [Axis] Regulatory Liability [Axis] Minnesota Solar Energy Standard - Qualifying Capacity for Small Scale Solar Mandate (MW) Solar Energy Standard Mandate, Qualifying Capacity for Small Scale Solar Mandate The maximum amount of nameplate capacity of a solar device to qualify for counting towards the small scale solar mandate of Minnesota's solar energy standard. Minnesota Solar Energy Standard - Overall Mandate Percentage Solar Energy Standard Mandate, Overall Mandate Percentage Minnesota's solar energy mandate for total retail electric sales, excluding sales to certain industrial customers, by the end of 2020. Service Cost Defined Benefit Plan, Service Cost Deferred Tax Assets [Member] SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member] Common Stock Reserved (Shares) Common Stock, Capital Shares Reserved for Future Issuance Cash and Cash Equivalents [Member] Cash and Cash Equivalents [Member] Entity Voluntary Filers Entity Voluntary Filers Non-Jurisdictional Land Sales Non-Jurisdictional Land Sales [Member] Non-Jurisdictional Land Sales Calpine Corporation [Member] Calpine Corporation [Member] Calpine Corporation Segment Reporting [Abstract] Segment Reporting [Abstract] Output Being Purchased - Electric Capacity (MW) Long-term Contract for Purchase of Electric Capacity (MW) Long-term Contract for Purchase of Electric Capacity (MW) Change in Benefit Obligation [Roll Forward] Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Defined Benefit Plan Contributions by Plan Participants, Excluding Key Employees Defined Benefit Plan Contributions by Plan Participants, Excluding Key Employees Defined Benefit Plan Contributions by Plan Participants, Excluding Key Employees Plan Asset Categories [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Axis] Defined Benefit Plan, Plan Assets, Category [Axis] Amortization from the Remeasurement of Deferred Income Taxes for Equity Method Investments Amortization from the Remeasurement of Deferred Income Taxes for Equity Method Investments Amortization from the Remeasurement of Deferred Income Taxes for Equity Method Investments Discount Rate Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate Amortization of Loss Defined Benefit Plan, Amortization of Gain (Loss) Total Liabilities and Equity Liabilities and Equity Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Customer Class [Domain] Customer Class [Domain] Customer Class [Domain] [Domain] for Customer Class [Axis] description of customer types or classes Basin Electric Cooperative PSA June 2022 - May 2023 [Member] Basin Electric Cooperative PSA June 2022 - May 2023 [Member] Basin Electric Cooperative PSA June 2022 - May 2023 [Member] Estimated Costs of Compliance Site Contingency, Loss Exposure Not Accrued, Best Estimate Gross Deferred Income Tax Assets Deferred Tax Assets, Gross Schedule of Error Corrections and Prior Period Adjustment Restatement [Table] Schedule of Error Corrections and Prior Period Adjustment Restatement [Table] Lessee, Operating Lease, Residual Value Guarantee, Description Lessee, Operating Lease, Residual Value Guarantee, Description Regulatory Differences – Excess Deferred Tax Benefit Effective Income Tax Rate Reconciliation, Regulatory Differences Regulatory Differences contributing to difference in effective tax rate to federal statutory rate. Power Purchase Agreements [Table] Long-Term Contracts for Purchase of Electric Power [Table] Concentration Risks, Types, No Concentration Percentage [Abstract] Concentration Risks, Types, No Concentration Percentage [Abstract] ESOP Compensation Expense Employee Stock Ownership Plan (ESOP), Compensation Expense Less: Imputed Interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Net Income Attributable to ALLETE Net Income (Loss) Available to Common Stockholders, Diluted Diluted Earnings Per Share of Common Stock Earnings Per Share Earnings Per Share, Diluted Defined Benefit Pension and Other Postretirement Benefit Expense Pension and Other Postretirement Benefits Cost (Reversal of Cost) First Mortgage Bonds - 3.86% Series Due 2030 [Member] ALLETE Bonds 3.86% Due September 2030 [Member] ALLETE Bonds 3.86% Due September 2030 [Member] Accumulated Benefit Obligation Defined Benefit Plan, Accumulated Benefit Obligation Vesting Period (Years) Performance Period (Years) Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period Equity Issuance Costs Payments of Stock Issuance Costs Consolidation Items [Axis] Consolidation Items [Axis] Residential [Member] Residential [Member] Revenue Recognized From Residential Customers 2024 Lessee, Operating Lease, Liability, to be Paid, Year Two Prepayments and Other Other Assets, Current Balance at January 1 Balance as of December 31 Unrecognized Tax Benefits Total Deferred Income Tax Assets Deferred Tax Assets, Net of Valuation Allowance Fuel Adjustment Clause Fuel Adjustment Clause [Member] Fuel Adjustment Clause Equity Securities [Member] Equity Securities [Member] Oconto Electric Cooperative [Member] Oconto Electric Cooperative [Member] Oconto Electric Cooperative Pro Rata Share of PPA Counterparty Interest Expense Long-Term Contract for Purchase of Electric Power, Interest Included in Contract Charges First Mortgage Bonds - 5.69% Series Due 2036 [Member] 5.69% Series Due 2036 [Member] First Mortgage Bonds, 5.69% Series Due 2036 [Member] Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Lessee, Operating Lease, Liability, Maturity [Table Text Block] Lessee, Operating Lease, Liability, Maturity [Table Text Block] Material Changes to Unrecognized Tax Benefits Expected During Next 12 Months Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit Entity Address, Address Line Entity Address, Address Line One Available-for-sale Securities, Debt Maturities, After One Year Through Three Years, Fair Value Available-for-sale Securities, Debt Maturities, After One Year Through Three Years, Fair Value Amount of available-for-sale debt securities at fair value maturing after the first fiscal year through the third fiscal year following the latest fiscal year (maturing in more than one year to less than three years). Large Power Customer Contracts Large Power Customer Contracts Large Power Customer Contracts Capitalized Share-Based Compensation Costs Share-Based Payment Arrangement, Amount Capitalized Retail Customers [Member] Retail [Member] Product and Service [Axis] Product and Service [Axis] Revenue from Cost Recovery Riders CIP Financial Incentive Regulated Operating Revenue, Other Municipal [Member] Municipal [Member] Municipal Sales Channel Class of Stock [Domain] Class of Stock [Domain] Expected Return on Plan Assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Other Noncurrent Assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets Customer Type [Axis] Customer Type [Axis] Customer Type [Axis] Interest Expense Interest Expense Interest Expense Equity Method Investments [Policy Text Block] Equity Method Investments [Policy Text Block] Alternative Revenue Program, Required Collection Period Alternative Revenue Program, Required Collection Period Alternative Revenue Program, Required Collection Period Retirement Plan Type [Axis] Retirement Plan Type [Axis] Capitalized Contract Cost [Axis] Capitalized Contract Cost [Axis] Long-term Debt [Table Text Block] Schedule of Long-Term Debt Instruments [Table Text Block] Minimum Payments in 2025 Unrecorded Unconditional Purchase Obligation, to be Paid, Year Three Funded Status, End of Year Total Net Pension Amounts Recognized in Consolidated Balance Sheet Total Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet Defined Benefit Plan, Funded (Unfunded) Status of Plan Equity Method Investment, Indicators of Impairment Equity Method Investment, Other than Temporary Impairment Manitoba Hydro PPA (expires 2040) [Member] Manitoba Hydro PPA (expires 2040) [Member] Manitoba Hydro PPA (expires 2040) [Member] MPUC [Member] MPUC [Member] Minnesota Public Utilities Commission [Member] Plant Removal Obligations [Member] Removal Costs [Member] Total Deferred Income Tax Liabilities Deferred Tax Liabilities, Gross Regulatory Assets and Liabilities [Line Items] Regulatory Assets and Liabilities [Line Items] Regulatory Assets and Liabilities [Line Items] Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] FERC [Member] FERC [Member] Federal Energy Regulatory Commission [Member] Fuel Adjustment Clause Public Utilities, Fuel Adjustment Clause Public Utilities, fuel adjustment clause regulatory liability Other – Non-utility Revenue Not from Contract with Customer, Other Common Stock, Par Value Per Share Common Stock, No Par Value Dilutive Securities (Shares) Weighted Average Number of Shares Outstanding, Diluted, Adjustment Schedule II [Text Block] SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] Assumptions Used to Determine Net Periodic Benefit Costs [Abstract] Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract] Projected Benefit Obligation Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation Measurement Frequency [Axis] Measurement Frequency [Axis] Sale of Energy under PSA [Member] Sale of Energy under PSA [Member] Sale of Energy under PSA [Member] Property, Plant and Equipment Impairment [Policy Text Block] Property, Plant and Equipment, Impairment [Policy Text Block] Trade Accounts Receivable [Member] SEC Schedule, 12-09, Allowance, Credit Loss [Member] Weighted-Average Grant Date Fair Value [Abstract] Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] FERC Authorized Return on Common Equity FERC Authorized Return on Common Equity FERC Authorized Return on Common Equity Other Other Accrued Liabilities, Current Total Unrecognized Postretirement Health and Life Cost Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax Long-Term Debt - Unamortized Debt Issuance Costs Debt Issuance Costs, Noncurrent, Net Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] PSCW [Member] PSCW [Member] Public Service Corporation of Wisconsin [Member] Retirement Benefits [Abstract] Retirement Benefits [Abstract] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Operating Expense Equity Method Investment, Summarized Financial Information, Operating Expense The amount of the operating expense reported by an equity method investment of the entity. Income Taxes Computed at Statutory Federal Rate Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Capitalized Asset Retirement Costs Costs Incurred, Capitalized Asset Retirement Obligation Costs Amount of asset retirement obligation costs incurred that were capitalized during the period. This may include liabilities incurred and revisions in cash flow estimates. Financing Activities Net Cash Provided by (Used in) Financing Activities [Abstract] Output Being Purchased - Electric Energy and Capacity (MW) Long-term Contract for Purchase of Electric Energy and Capacity (MW) Long-term Contract for Purchase of Electric Energy and Capacity (MW) Unearned Grant Award Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Unearned Grant Award, Weighted Average Grant Date Fair Value Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Unearned Grant Award, Weighted Average Grant Date Fair Value (Per Share) Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] Number of Customers Number of Large Power Customers Number of Customers Number of Customers Equity Investments [Text Block] Equity Method Investments and Joint Ventures Disclosure [Text Block] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Impairment of Property, Plant and Equipment Loss on Impairment of Assets Asset Impairment Charges Other Long-Term Debt, 2.16% – 4.58% Due 2022 – 2051 [Member] Other Long-Term Debt [Member] Other long-term debt instruments not specifically identified elsewhere Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] VEBA [Member] VEBA [Member] VEBA (Voluntary Employee Benefits Association trusts) [Member] Allowed Indebtedness to Total Capitalization Ratio Debt Instrument, Required Indebtedness to Total Capital Ratio Indebtedness to total capital ratio required to be maintained by most restrictive financial covenant. Minnesota Solar Energy Standard - Small Scale Solar Mandate Percentage Solar Energy Standard Mandate, Small Scale Solar Mandate Percentage Minnesota's solar energy mandate for small scale solar with photovoltaic devices with a nameplate capacity of 20 kilowatts or less by the end of 2020. Expressed as a percentage of the overall mandate. Contract with Customer, Sales Channel [Domain] Contract with Customer, Sales Channel [Domain]