Non-Controlling Interest in Subsidiaries Effective Income Tax Rate Reconciliation, Noncontrolling Interest Income (Loss), Amount Available-for-sale Securities, Debt Maturities, within One Year, Fair Value Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Payments for Purchase of Available-for-sale Securities Payments for Purchase of Available-for-sale Securities Payments for Purchase of Available-for-sale Securities Consolidated Statement of Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Net Income Net Income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Changes in Regulatory and Other Non-Current Liabilities Increase (Decrease) in Other Noncurrent Liabilities Bad Debt Expense Accounts Receivable, Credit Loss Expense (Reversal) Long-Term Debt - Principal Long-Term Debt, Gross 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] 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] Basis Point Incentive adder Basis Point Incentive adder Basis Point Incentive adder Debt Instrument [Axis] Debt Instrument [Axis] Dividends on Common Stock Common Stock Dividends Payments of Ordinary Dividends, Common Stock Square Butte [Member] Square Butte [Member] Square Butte [Member] Other [Member] Other [Member] Regulated Operations Other Revenue Recognized From Other Sources Immaterial For Disaggregation Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Other [Member] ALLETE Clean Energy Other [Member] ALLETE Clean Energy Other Revenue Recognized From Other Sources Immaterial For Disaggregation [Member] Inventories – Net [Abstract] Inventory, Net [Abstract] Power Purchase Agreements [Domain] Power Purchase Agreement - Energy and Capacity [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 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 Other Income [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] Long-term Contract for Purchase of Electric Power, Term of Contract (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. Depreciation Expense Depreciation Public Utilities, Approved Rate Increase (Decrease), Amount Public Utilities, Approved Rate Increase (Decrease), Amount Cash Contributions to Defined Benefit Pension Plans Payment for Pension Benefits Minnesota Power [Member] Minnesota Power [Member] Minnesota Power [Member] Interest Rate Debt Instrument, Interest Rate, Stated Percentage Net Periodic Benefit Cost (Credit) Defined Benefit Plan, Net Periodic Benefit Cost (Credit) State Current State and Local Tax Expense (Benefit) Other Current Liabilities Increase (Decrease) in Other Current Liabilities Net Income Attributable to ALLETE Net Income Attributable ALLETE Net Income (Loss) Attributable to ALLETE Net Income (Loss) Attributable to Parent Other [Member] Other Income (Expense) - Other [Member] Other Income (Expense) - Other [Member] Contracts with Customers - Utility Regulated Operating Revenue Document and Entity Information [Line Items] Document Information [Line Items] Amortization of Prior Service Credits Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Subsequent Event Type [Axis] Subsequent Event Type [Axis] Long-term Contract [Member] Long-term Contract [Member] Long-term Contract Revenue Stream [Member] Minnkota Power PSA [Member] Minnkota Sales Agreement [Member] Minnkota Sales Agreement [Member] Equity Component [Domain] Equity Component [Domain] Rate Type [Domain] Rate Type [Domain] Rate Type [Domain] Environmental Remediation Contingency [Axis] Environmental Remediation Contingency [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Total Fair Value of Assets Assets, Fair Value Disclosure Nobles 2 [Member] Nobles 2 [Member] Nobles 2 [Member] Equity Method Investment [Domain] Investment, Name [Domain] Regulatory Assets and Liabilities Disclosure [Abstract] Regulatory Assets and Liabilities Disclosure [Abstract] Fair Value Measurement [Policy Text Block] Fair Value Measurement, Policy [Policy Text Block] Standby Letters of Credit [Member] Standby Letters of Credit [Member] 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). Supplemental Cash Flow Information [Abstract] Supplemental Cash Flow Information [Abstract] Number of Operating Segments Number of Operating Segments Regulated Operations [Abstract] Regulated Operations [Abstract] Surety Bonds [Member] Surety Bond [Member] Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Entity Address, State or Province Entity Address, State or Province Level 1 [Member] Fair Value, Inputs, Level 1 [Member] Other Current Liabilities [Table Text Block] Other Current Liabilities [Table Text Block] Other Comprehensive Income (Loss) [Abstract] Other Comprehensive Income (Loss), Net of Tax [Abstract] Operating and Maintenance Operating and Maintenance Operating and Maintenance Expenses 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 Power Purchased Utilities Operating Expense, Purchased Power under Long-Term Contracts Cash provided by (used in) Operating Activities Net Cash Provided by (Used in) Operating Activities Operating Lease Liabilities Operating Lease, Liability, Current Long-term PSA [Member] Long-term PSA [Member] Revenue Recognized From Long-term PSAs Industrial [Member] Industrial [Member] Industrial Sales Channel [Member] Increase (Decrease) in Income Tax Due to: [Abstract] Increase (Decrease) in Tax [Abstract] Increase (Decrease) in Tax [Abstract] Other Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount Investment in ATC [Line Items] Investment in Nobles 2 [Line Items] Schedule of Equity Method Investments [Line Items] Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] Sale of Wind Energy Facility Sale of Wind Energy Facility [Member] Sale of Wind Energy Facility Legal Entity [Axis] Legal Entity [Axis] Long-Term Debt Long-Term Debt - Total Long-Term Debt, Excluding Current Maturities Regulatory Assets and Liabilities [Policy Text Block] Public Utilities, Policy [Policy Text Block] Total Liabilities Liabilities Power Purchase Agreements [Axis] Power Purchase Agreement - Energy and Capacity [Axis] Long-Term Contract for Purchase of Electric Power [Axis] Geographical [Axis] Geographical [Axis] Investing Activities [Abstract] Net Cash Provided by (Used in) Investing Activities [Abstract] Defined Benefit Pension and Other Postretirement Benefit Plans Liability, Defined Benefit Plan, Noncurrent Common Stock Issued Stock Issued During Period, Value, New Issues Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Current Income Tax Expense (Benefit) [Abstract] Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Document Type Document Type Components of Net Periodic Benefit Cost (Credit) [Abstract] Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] Generating Facility Unit Name [Domain] Generating Facility Unit Name [Domain] [Domain] for Name of generating unit or facility [Axis] Materials and Supplies Inventory, Supplies, Net of Reserves Assets [Abstract] Assets, Fair Value Disclosure [Abstract] Business Segments [Axis] Segments [Axis] Short-Term and Long-Term Debt [Text Block] Debt Disclosure [Text Block] 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 Investments [Abstract] Investments [Abstract] Deferred Income Tax Benefit Total Deferred Income Tax Expense (Benefit) Deferred Income Tax Expense (Benefit) Other Income (Expense) - Other [Abstract] Other Income (Expense) - Other [Abstract] Other Income (Expense) - Other [Abstract] Taxes Other than Income Taxes Taxes, Other Goodwill, Change in Goodwill Allocation, Description Goodwill, Change in Goodwill Allocation, Description Superior, WI [Member] Superior, WI [Member] Superior, WI Subsequent Event [Member] Subsequent Event [Member] Document Period End Date Document Period End Date Total Assets Assets Assets Debt Disclosure [Abstract] Debt Disclosure [Abstract] Earnings Per Share [Abstract] Earnings Per Share [Abstract] Diamond Spring [Member] Diamond Spring [Member] Diamond Spring [Member] Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment, Tax Employer Contributions to Defined Benefit Plans Defined Benefit Plan, Plan Assets, Contributions by Employer Long-Term Debt - Unamortized Debt Issuance Costs Unamortized Debt Issuance Expense, Long-Term Debt Excluding Current Maturities The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of long-term debt excluding current maturities. Non-Controlling Interest Details [Line Items] Non-Controlling Interest Details [Line Items] [Line Items] for Non-Controlling Interest Details [Table] 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 Long-Term Debt Due Within One Year Long-Term Debt, Current Maturities Cash provided by (used in) Financing Activities Net Cash Provided by (Used in) Financing Activities Production Tax Credits Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount Short-Term and Long-Term Debt - Fair Value Long-Term Debt, Fair Value Non-Controlling Interest Details [Table] Non-Controlling Interest Details [Table] Non-Controlling Interest Details [Table] Line of Credit [Member] Line of Credit [Member] Income Before Income Taxes Income Before Income Taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Equity [Abstract] Stockholders' Equity Attributable to Parent [Abstract] Business Segments [Domain] Segments [Domain] Manufactured Gas Plant - Current Manufactured Gas Plant - Current Manufactured Gas Plant - Current Earnings Per Share and Common Stock [Text Block] Earnings Per Share [Text Block] Other Current Liabilites [Abstract] Other Liabilities, Current [Abstract] Document and Entity Information [Abstract] Document and Entity Information [Abstract] Document and Entity Information [Abstract] Interest Cost Defined Benefit Plan, Interest Cost Total Regulatory Asset [Domain] Regulatory Asset [Domain] Cash and Cash Equivalents, Policy [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 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] Fair Value, by Balance Sheet Grouping [Table Text Block] Fair Value, by Balance Sheet Grouping [Table Text Block] Regulated Operations [Member] Regulated Operations [Member] Regulated Operations [Member] Other Non-Current Assets [Table Text Block] Schedule of Other Assets, Noncurrent [Table Text Block] Entity Registrant Name Entity Registrant Name Fuel Adjustment Clause (Member) Regulatory Clause Revenues, under-Recovered [Member] Regulatory Agency [Axis] Regulatory Agency [Axis] 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. Uncertain Tax Positions [Policy Text Block] Income Tax Uncertainties, Policy [Policy Text Block] 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. 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. Pension and Other Postretirement Benefit Plans [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Coal, Rail and Shipping Contracts [Line Items] Unrecorded Unconditional Purchase Obligation [Line Items] Component of Other Income (Expense) - Other [Axis] Component of Other Income (Expense) - Other [Axis] Component of Other Income (Expense) - Other [Axis] Entity Address, City or Town Entity Address, City or Town Pension and Other Postretirement Benefit Plans [Text Block] Retirement Benefits [Text Block] Operating Expenses [Abstract] Operating Expenses [Abstract] Total Equity Balance, Beginning Balance Balance, End of Period Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Revenue Streams [Axis] Contract with Customer, Sales Channel [Axis] Expected Output Entitlement Long-Term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased Minimum [Member] Minimum [Member] Non-Controlling Interest in Subsidiaries Stockholders' Equity Attributable to Noncontrolling Interest Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Entity Emerging Growth Company Entity Emerging Growth Company Commercial [Member] Commercial [Member] Revenue Recognized From Commercial Customers Actual Ratio of Indebtedness to Total Capitalization Debt Instrument, Actual Indebtedness to Total Capital Ratio Actual indebtedness to total capital ratio required to be maintained by most restrictive financial covenant. Asset Retirement Obligation Asset Retirement Obligations, Noncurrent Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Business Segments [Table] Schedule of Segment Reporting Information, by Segment [Table] Pension [Member] Pension Plan [Member] Annual Additional Revenue Generated from Requested Final Rate Increase Public Utilities, Requested Rate Increase (Decrease), Amount CIP Consolidated Filing Member CIP Consolidated Filing Member [Member] CIP Consolidated Filing Member Equity Method Investment [Axis] Investment, Name [Axis] Fair Value [Text Block] Fair Value Disclosures [Text Block] Other - Non-utility Amortization of PSAs Amortization of Power Purchase Agreements The amount of income recognized in the current period that reflects income associated with the reduced liability of the PPAs acquired in a business acquisition. As noncash income, this element is subtracted from net income when calculating cash provided by or used in operations using the indirect method. Trading Symbol Trading Symbol Entity File Number Entity File Number Environmental Matters [Line Items] Environmental Matters [Line Items] [Line Items] for Environmental Matters [Table] 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] Net Loss Attributable to Non-Controlling Interest Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Effective Tax Rate Effective Income Tax Rate Reconciliation, Percent Short-Term Debt - Principal Debt, Current, Gross Amount of short-term debt and current maturities of long-term debt before deduction of unamortized discount or premium and unamortized debt issuance costs. Total Debt - Principal Debt, Long-Term and Short-Term, Combined Amount, Gross Represents the aggregate of total long-term debt, including current maturities and short-term debt, before deduction of unamortized discount or premium and unamortized debt issuance expense. ALLETE Bonds 4.98% Due April 2033 ALLETE Bonds 4.98% Due April 2033 [Member] ALLETE Bonds 4.98% Due April 2033 Other Income (Expense) [Abstract] Other Nonoperating Income (Expense) [Abstract] Customer Refund Liability, Current Customer Refund Liability, Current Accounts Payable Increase (Decrease) in Accounts Payable Equity Method Investments and Joint Ventures [Abstract] Equity Method Investments and Joint Ventures [Abstract] Total Operating Revenue Operating Revenue Revenues Fuel, Purchased Power and Gas - Utility Fuel, Purchased Power and Gas - Utility Fuel, Purchased Power and Gas - Utility Current Regulatory Assets Regulatory Asset, Current Income Tax Expense [Text Block] Income Tax Disclosure [Text Block] Other Power Suppliers [Member] Other Power Suppliers [Member] Other Power Suppliers Sales Channel [Member] State Deferred State and Local Income Tax Expense (Benefit) Loss (Gain) on Investments and Property, Plant and Equipment Gain (Loss) on Disposition of Other Assets Cash Paid for Interest – Net of Amounts Capitalized Interest Paid, Excluding Capitalized Interest, Operating Activities Basic Earnings Per Share of Common Stock 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). Total Debt - Total Debt, Long-Term and Short-Term, Combined Amount Investment in ATC [Table] Investment in Nobles 2 [Table] Schedule of Equity Method Investments [Table] Inventories – Net [Policy Text Block] Inventory, Policy [Policy Text Block] Operating Revenue, Other Than Customer Revenue Revenue, Other Than Customer Revenue Non-cash Revenue Recognized From Amortization of PSAs Assumed Through Acquisitions ALLETE, Inc. [Member] ALLETE, Inc. [Member] -- None. No documentation exists for this element. -- Counterparty Name [Domain] Counterparty Name [Domain] Short-Term Debt - Unamortized Debt Issuance Costs Unamortized Debt Issuance Expense, Debt, Current The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of short-term debt or the current maturities of long-term debt. Total ALLETE Equity Stockholders' Equity Attributable to Parent Square Butte PPA [Member] Square Butte PPA [Member] Long-term contract with Square Butte for the purchase of electric power. New Energy New Energy [Member] New Energy Entity Interactive Data Current Entity Interactive Data Current Fair Value of Financial Instruments [Table] Fair Value, by Balance Sheet Grouping [Table] Document and Entity Information, Document [Axis] Document Information, Document [Axis] Changes in Operating Assets and Liabilities [Abstract] Increase (Decrease) in Operating Capital [Abstract] Other Other Assets, Miscellaneous, Noncurrent Retained Earnings [Member] Retained Earnings [Member] Business Segments [Line Items] Segment Reporting Information [Line Items] Change in Cash, Cash Equivalents and Restricted Cash Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect Common Stock [Member] Common Stock [Member] Wholesale and Retail Contra AFUDC [Member] Wholesale and Retail Contra AFUDC [Member] Wholesale and Retail Contra AFUDC [Member] Number of Reportable Segments Number of Reportable Segments Regulatory Liability [Domain] Regulatory Liability [Domain] Cost Recovery Riders [Member] Cost Recovery Riders [Member] Cost Recovery Riders [Member] Income Tax [Policy Text Block] Income Tax, Policy [Policy Text Block] Fuel Energy Related Inventory, Coal Consolidated Statement of Equity [Table] Statement [Table] 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] Approximate Annual Reduction in Pretax Income for FERC Proposal to Limit Incentive adder, ALLETE's Proportionate Share Approximate Annual Reduction in Pretax Income for FERC Proposal to Limit Incentive adder, ALLETE's Proportionate Share Approximate Annual Reduction in Pretax Income for FERC Proposal to Limit Incentive adder, ALLETE's Proportionate Share Document Quarterly Report Document Quarterly Report Current Assets [Abstract] Assets, Current [Abstract] Operating Lease Liabilities Operating Lease, Liability, Noncurrent Wind Turbine Generators [Member] Wind Turbine Generators [Member] Wind Turbine Generators [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Contract Assets Contract with Customer, Asset, after Allowance for Credit Loss, Noncurrent Retained Earnings Retained Earnings (Accumulated Deficit) Tenaska [Member] Tenaska [Member] Tenaska Energy, Inc. and Tenaska Energy Holdings, LLC [Member] Accounts Receivable (Less Allowance of $1.7 and $1.6) Accounts Receivable, after Allowance for Credit Loss, Current Equity Components [Axis] Equity Components [Axis] Proceeds from Non-controlling Interest in Subsidiaries - Net Proceeds from Non-controlling Interest in Subsidiaries - Net of Issuance Costs Proceeds from Noncontrolling Interests Recurring Fair Value Measures [Member] Fair Value, Recurring [Member] Capitalized Asset Retirement Costs Increase (Decrease) in Asset Retirement Obligations 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 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). Approved Return on Common Equity Authorized Return on Equity Public Utilities, Approved Return on Equity, Percentage Document Fiscal Year Focus Document Fiscal Year Focus Regulatory Agency [Domain] Regulatory Agency [Domain] Operating Activities [Abstract] Net Cash Provided by (Used in) Operating Activities [Abstract] 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 Total Other Expense Nonoperating Income (Expense) Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] 2022 Minnesota General Rate Review 2022 Minnesota General Rate Review [Member] 2022 Minnesota General Rate Review Defined Benefit Pension and Postretirement Benefit Pension and Other Postretirement Benefits Expense (Reversal of Expense), Noncash Total Current Income Tax Expense Current Income Tax Expense (Benefit) Operating Lease, Right-of-Use Asset Operating Lease, Right-of-Use Asset Accumulated Other Comprehensive Loss [Member] AOCI Attributable to Parent [Member] Regulatory Asset [Axis] Regulatory Asset [Axis] Document Transition Report Document Transition Report Local Phone Number Local Phone Number Accounts Receivable [Abstract] Accounts Receivable, after Allowance for Credit Loss, Current [Abstract] Coal Combustion Residuals [Member] Coal Combustion Residuals [Member] Coal Combustion Residuals [Member] Operating Income Operating Income (Loss) Inventories Increase (Decrease) in Inventories ATC [Member] ATC [Member] ATC [Member] Prepayments and Other Increase (Decrease) in Prepaid Expense and Other Assets Document and Entity Information [Table] Document Information [Table] Common Stock, Shares Outstanding Common Stock, Shares, Outstanding AFUDC – Equity AFUDC–Equity Increase (Decrease) in Allowance for Equity Funds Used During Construction Goodwill Goodwill Total Fair Value of Liabilities Liabilities, Fair Value Disclosure Guarantee Entity and Type [Domain] Guarantee Entity and Type [Domain] [Domain] for Guarantee Entity and Type [Axis] Income Tax Benefit Total Income Tax Expense (Benefit) Income Tax Expense (Benefit) Geographical [Domain] Geographical [Domain] Cash Equivalents Other Restricted Assets, Noncurrent Public Utilities Reserve for Interim Rates Public Utilities Reserve for Interim Rates Public Utilities Reserve for Interim Rates Income Statement [Abstract] Income Statement [Abstract] Federal Deferred Federal Income Tax Expense (Benefit) Document Fiscal Period Focus Document Fiscal Period Focus Restricted Cash included in Other Non-Current Assets Restricted Cash, Non-Current Restricted Cash, Noncurrent Cost of Sales - Non-utility Cost of Goods and Services Sold ALLETE's Investment in ATC [Roll Forward] ALLETE's Investment in ATC [Roll Forward] ALLETE's Investment in ATC [Roll Forward] Diluted (Shares) Weighted Average Number of Shares Outstanding, Diluted Guarantor Obligations [Line Items] Guarantor Obligations [Line Items] Minnkota Power [Member] Minnkota Power [Member] Minnkota Power [Member] Inventories – Net [Table Text Block] Schedule of Inventory, Current [Table Text Block] Regulatory Assets Non-Current Regulatory Assets Regulatory Asset, Noncurrent Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] Available-for-sale - Equity Securities Equity Securities, FV-NI, Noncurrent Current Regulatory Liabilities Regulatory Liability, Current Common Stock Without Par Value, 80.0 Shares Authorized, 57.3 and 57.2 Shares Issued and Outstanding Common Stock, Value, Issued Interest and Investment Income (Loss) [Member] Interest and Investment Earnings [Member] Interest and Investment Earnings [Member] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Guarantee Entity and Type [Axis] Guarantee Entity and Type [Axis] Guarantee Entity and Type [Axis] Recurring Fair Value Measures [Table Text Block] Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Boswell Units 1 and 2 Net Plant and Equipment Boswell Units 1 and 2 Net Plant and Equipment [Member] Boswell Units 1 and 2 Net Plant and Equipment Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents 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) Net Loss Attributable to Non-Controlling Interest Net Income (Loss) Attributable to Noncontrolling Interest Current Liabilities [Abstract] Liabilities, Current [Abstract] Proceeds from Issuance of Short-Term and Long-Term Debt Proceeds from Issuance of Long-Term Debt Equity Method Investments (Table Text Block) Equity Method Investments [Table Text Block] Common Stock, Shares Issued Common Stock, Shares, Issued Equity Investments Equity Investment Balance as of December 31, 2022 Equity Investment Balance as of March 31, 2023 Equity Investment Balance Equity Method Investments Regulatory Matters [Table] Public Utilities General Disclosures [Table] Customer Deposits Contract with Customer, Liability, Current Other Postretirement Benefit Plans Other Postretirement Benefit Plans Other Postretirement Benefit Plans Retirement Plan Type [Domain] Retirement Plan Type [Domain] Recurring Fair Value Measures [Abstract] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Amendment Flag Amendment Flag Cash used in Investing Activities Net Cash Provided by (Used in) Investing Activities Environmental Remediation Contingency [Domain] Environmental Remediation Contingency [Domain] Requested Equity Capital Structure Public Utilities, Requested Equity Capital Structure, Percentage Total Other Comprehensive Income (Loss) Other Comprehensive Income (Loss), Net of Tax Corporate and Other [Member] Corporate and Other [Member] Total Comprehensive Income Attributable to ALLETE Comprehensive Income (Loss), Net of Tax, Attributable to Parent Business Segments [Table Text Block] Schedule of Segment Reporting Information, by Segment [Table Text Block] Defined Benefit Pension and Other Postretirement Benefit Plans, Income Tax Expense Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax Entity Current Reporting Status Entity Current Reporting Status Asset Retirement Obligations [Member] Asset Retirement Obligation Costs [Member] Other Total Other Current Liabilities Other Liabilities, Current Other Non-Current Assets Total Other Non-Current Assets Other Assets, Noncurrent Glen Ullin Energy Center [Member] Glen Ullin Energy Center [Member] Glen Ullin Energy Center [Member] Depreciation and Amortization Depreciation, Depletion and Amortization Environmental Accruals [Policy Text Block] Environmental Costs, Policy [Policy Text Block] Statutory Federal Income Tax Rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Pension and Other Postretirement Benefit Plans Non-Service Credit [Member] Pension and Other Postretirement Benefit Plans Non-Service Credit [Member] Pension and Other Postretirement Benefit Plans Non-Service Credit [Member] Counterparty Name [Axis] Counterparty Name [Axis] Power Purchase Agreements [Line Items] Long-Term Contract for Purchase of Electric Power [Line Items] Goodwill and Intangible Assets - Net Intangible Assets, Net (Including Goodwill) State of Incorporation Entity Incorporation, State or Country Code Power Sales Agreements - Energy and Capacity [Domain] Long-term Contracts for Sale of Electric Power [Domain] [Domain] for Long-term Contracts for Sale of Electric Power [Axis] Liabilities [Abstract] Liabilities [Abstract] Property, Plant and Equipment – Net Property, Plant and Equipment, Net Repayments of Short-Term and Long-Term Debt Repayments of Long-Term Debt Changes in Regulatory and Other Non-Current Assets Increase (Decrease) in Other Noncurrent Assets Defined Benefit Pension and Other Postretirement Benefit Plans - Net of Income Tax Expense of $- and $0.1 Defined Benefit Pension and Other Postretirement Plans Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Taconite Harbor Energy Center Taconite Harbor Energy Center [Member] Taconite Harbor Energy Center Accounts Receivable, Allowance Accounts Receivable, Allowance for Credit Loss, Current Short-Term and Long-Term Debt - Carrying Amount Long-Term Debt Other Total Other Income Other Nonoperating Income (Expense) Operations and Significant Accounting Policies [Text Block] Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Common Stock, Shares Authorized Common Stock, Shares Authorized Guarantor Obligations [Table] Schedule of Guarantor Obligations [Table] Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Maximum [Member] Maximum [Member] Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Income (Loss), Net of Tax Cash and Cash Equivalents Cash and Cash Equivalents, at Carrying Value Total Current Assets Assets, Current Accrued Taxes Taxes Payable, Current Pension 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 Income Taxes Paid Income Taxes Paid, Net Proceeds from Sale of Available-for-sale Securities Cash Proceeds from Sale of Available-for-sale Securities Cash Proceeds from Sale of Available-for-sale Securities Entity Small Business Entity Small Business Measurement Frequency [Domain] Measurement Frequency [Domain] Components of Net Periodic Benefit Expense (Income) [Table Text Block] Schedule of Net Benefit Costs [Table Text Block] Dividends Per Share of Common Stock Common Stock, Dividends, Per Share, Declared Operating Revenues [Abstract] Revenues [Abstract] Distributions to Non-controlling Interest Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Regulatory Liabilities Non-Current Regulatory Liabilities Regulatory Liability, Noncurrent Uncertain Tax Positions [Abstract] Income Tax Uncertainties [Abstract] Supplemental Statement of Cash Flows Information [Table Text Block] Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Other [Member] Corporate & Other - Other [Member] Revenue Recognized by Corporate & Other From Other Sources Immaterial for Disaggregation Power Purchase Agreements [Policy Text Block] Consolidation, Variable Interest Entity, Policy [Policy Text Block] Regulatory Matters [Line Items] Public Utilities, General Disclosures [Line Items] SWL&P [Member] SWL&P [Member] Superior, Water, Light and Power [Member] 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] Title of 12(b) Security Title of 12(b) Security Consolidated Entities [Axis] Consolidated Entities [Axis] Other Income (Expense) - Other [Table] Other Income (Expense) - Other [Table] Other Income (Expense) - Other [Table] 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 Debt Instrument [Line Items] Debt Instrument [Line Items] Common Stock [Abstract] Common Stock, Number of Shares, Par Value and Other Disclosure [Abstract] 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] Business Segments [Text Block] Segment Reporting Disclosure [Text Block] Commitments, Guarantees and Contingencies [Text Block] Commitments Contingencies and Guarantees [Text Block] Other Receivables Other Receivables Liabilities and Equity [Abstract] Liabilities and Equity [Abstract] Generation Type [Domain] Generation Type [Domain] [Domain] for Generation Type [Axis] Recurring Fair Value Measures [Table] Fair Value, Recurring and Nonrecurring [Table] South Peak [Member] South Peak [Member] South Peak [Member] Pension and Other Postretirement Plan Costs [Member] Pension and Other Postretirement Plans Costs [Member] Inventories – Net Total Inventories – Net Inventory, Net Proceeds from Issuance of First Mortgage Bond Proceeds from Issuance of First Mortgage Bond Power Sales Agreements - 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 Comprehensive Income [Abstract] Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] Other Other Accrued Liabilities, Noncurrent BNI Energy Reclamation Liability [Member] BNI Coal Reclamation Liability [Member] Reclamation liability for closing costs associated with BNI Coal mine and mine facilities. Estimated Costs of Compliance (Accrued) Accrual for Environmental Loss Contingencies Entity Filer Category Entity Filer Category Proceeds from Issuance of Common Stock Proceeds from Issuance of Common Stock Basic (Shares) Weighted Average Number of Shares Outstanding, Basic Federal Current Federal Tax Expense (Benefit) Caddo [Member] Caddo [Member] Caddo Liabilities [Abstract] Liabilities, Fair Value Disclosure [Abstract] Ownership Percentage Equity Method Investment, Ownership Percentage Commitments, Guarantees and Contingencies (Note 6) Commitments and Contingencies Name of Exchange Security Exchange Name Requested Rate Increase Percent Public Utilities, Requested Rate Increase (Decrease), Percentage Fair Value of Financial Instruments [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Letters of Credit Outstanding, Amount Letters of Credit Outstanding, Amount Restricted Cash included in Prepayments and Other Restricted Cash, Current Schedule of Short-Term and Long-Term Debt [Table Text Block] Schedule of Debt [Table Text Block] Operating Revenue Revenue from Contract with Customer, Excluding Assessed Tax Renewable Energy Facilities Under Development Other Inventory, Gross Coal, Rail and Shipping Contracts [Axis] Unrecorded Unconditional Purchase Obligation by Category of Item Purchased [Axis] Regulatory Liability [Axis] Regulatory Liability [Axis] Service Cost Defined Benefit Plan, Service Cost Short-Term Debt - Total Debt, Current Schedule of Long-term Debt Instruments [Table] Financial Covenants [Table] Schedule of Long-Term Debt Instruments [Table] Level 3 [Member] Fair Value, Inputs, Level 3 [Member] Provision for Interim Rate Refund Provision (Payment) for Interim Rate Refund Provision (Payment) for Interim Rate Refund Available-for-sale – Corporate and Governmental Debt Securities (b) Debt Securities, Available-for-Sale, Noncurrent Square Butte Coal-fired Unit [Member] Square Butte Coal-fired Unit [Member] Square Butte Coal-fired Unit located near Center, North Dakota Non-Jurisdictional Land Sales Non-Jurisdictional Land Sales [Member] Non-Jurisdictional Land Sales Segment Reporting [Abstract] Segment Reporting [Abstract] Contracts with Customers - Non-utility Unregulated Operating Revenue Customer Class [Axis] Customer Class [Axis] Customer Class [Axis] description of customer types or classes Non-controlling Interest [Member] Noncontrolling Interest [Member] Amortization of the Remeasurement of Deferred Income Taxes Amortization from the Remeasurement of Deferred Income Taxes for Equity Method Investments Amortization from the Remeasurement of Deferred Income Taxes for Equity Method Investments Amortization of Net Loss Defined Benefit Plan, Amortization of Gain (Loss) Total Liabilities and Equity Liabilities and Equity Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Axis] Customer Class [Domain] Customer Class [Domain] [Domain] for Customer Class [Axis] description of customer types or classes Estimated Costs of Compliance Site Contingency, Loss Exposure Not Accrued, Best Estimate Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Level 2 [Member] Fair Value, Inputs, Level 2 [Member] Regulatory Differences – Excess Deferred Tax Effective Income Tax Rate Reconciliation, Regulatory Differences Regulatory Differences contributing to difference in effective tax rate to federal statutory rate. Power Purchase Agreements [Table] Long-Term Contracts for Purchase of Electric Power [Table] Current Fiscal Year End Date Current Fiscal Year End Date Deferred Income Taxes Deferred Income Taxes and Other Tax Liabilities, Noncurrent Net Income Attributable to ALLETE Net Income (Loss) Available to Common Stockholders, Diluted Fuel Adjustment Clause Increase (Decrease) in Regulatory Clause Revenue Diluted Earnings Per Share of Common Stock Earnings Per Share, Diluted Environmental Matters [Table] Environmental Matters [Table] Environmental Matters [Table] Public Utilities, Approved Equity Capital Structure, Percentage Public Utilities, Approved Equity Capital Structure, Percentage Coal, Rail and Shipping Contracts [Domain] Unconditional Purchase Obligation, Category of Goods or Services Acquired [Domain] Residential [Member] Residential [Member] Revenue Recognized From Residential Customers Total Current Liabilities Liabilities, Current Prepayments and Other Other Assets, Current Gross Unrecognized Tax Benefits Unrecognized Tax Benefits Fuel Adjustment Clause [Member] Fuel Adjustment Clause [Member] Amount expected to be refunded to customers for the over-collection of fuel adjustment clause recoveries. Gross Unrecognized Tax Benefits That Would Favorably Impact Effective Income Tax Rate Unrecognized Tax Benefits that Would Impact Effective Tax Rate Pro Rata Share of PPA Counterparty Interest Expense Long-Term Contract for Purchase of Electric Power, Interest Included in Contract Charges Other Non-Current Liabilities [Abstract] Other Liabilities, Noncurrent [Abstract] Generating Capacity Counterparty Owned (MW) Generating Capacity Counterparty Owned (MW) Generating Capacity Counterparty Owned (MW) Entity Address, Address Line One 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). Other Financing Activities Proceeds from (Payments for) Other Financing Activities Other Non-Current Assets [Abstract] Other Assets, Noncurrent [Abstract] Tenaska PPA [Member] Tenaska PPA [Member] Tenaska PPA [Member] Municipal [Member] Municipal [Member] Municipal Sales Channel Revenue from Cost Recovery Riders and Other Regulatory Programs Regulated Operating Revenue, Other Expected Return on Plan Assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets South Shore Energy South Shore Energy [Member] South Shore Energy Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Interest Expense Interest Expense Equity Method Investments [Policy Text Block] Equity Method Investments [Policy Text Block] Unrealized Loss on Securities - Net of Income Tax Expense $0.1 and $- Unrealized Loss on Securities OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax Retirement Plan Type [Axis] Retirement Plan Type [Axis] Cash, Cash Equivalents and Restricted Cash [Abstract] Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents [Abstract] Deferred Compensation Deferred Compensation, Fair Value Disclosure This element represents the portion of the balance sheet assertion, Deferred Compensation, valued at fair value by the entity. Entity Tax Identification Number Entity Tax Identification Number Total Debt - Unamortized Debt Issuance Costs Unamortized Debt Issuance Expense AFUDC - Equity [Member] AFUDC - Equity [Member] AFUDC - Equity [Member] MPUC [Member] MPUC [Member] Minnesota Public Utilities Commission [Member] ALLETE South Wind [Member] ALLETE South Wind [Member] ALLETE South Wind Plant Removal Obligations [Member] Removal Costs [Member] Regulatory Assets and Liabilities [Line Items] Regulatory Assets and Liabilities [Line Items] Regulatory Assets and Liabilities [Line Items] Consolidated Entities [Domain] Consolidated Entities [Domain] Estimated Obligation Guarantor Obligations, Maximum Exposure, Undiscounted Other (Member) Other Regulatory Assets (Liabilities) [Member] Common Stock, Par Value Common Stock, No Par Value 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 Dilutive Securities (Shares) Weighted Average Number of Shares Outstanding, Diluted, Adjustment Entity Central Index Key Entity Central Index Key Measurement Frequency [Axis] Measurement Frequency [Axis] Effective Income Tax Rate Reconciliation, Investment Tax Credits Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount Other Other Accrued Liabilities, Current Entity [Domain] Entity [Domain] City Area Code City Area Code Assets [Abstract] Assets [Abstract] Retirement Benefits [Abstract] Retirement Benefits [Abstract] Generating Facility [Axis] Generating Facility Axis [Axis] Name of generating unit or facility [Axis] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Line of Credit, Current Line of Credit, Current Unrecorded Unconditional Purchase Obligation [Table] Unrecorded Unconditional Purchase Obligation [Table] Income Taxes Computed at Statutory Federal Rate Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Financing Activities [Abstract] Net Cash Provided by (Used in) Financing Activities [Abstract] Earnings Per Share [Policy Text Block] Earnings Per Share, Policy [Policy Text Block] 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 Method Investments Cash Investments Payments to Acquire Equity Method Investments Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] Other Non-Current Liabilities Total Other Non-Current Liabilities Other Liabilities, Noncurrent Equity Investments [Text Block] Equity Method Investments and Joint Ventures Disclosure [Text Block] Equity Earnings Equity in ATC Earnings 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] Reconciliation of Basic and Diluted Earnings Per Share [Table Text Block] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Proceeds from Sale of Wind Project Proceeds from Sale of Other Assets Minnesota Cost Recovery Riders [Member] Current Cost Recovery Rider [Member] Current Cost Recovery Rider [Member] Required Ratio of Indebtedness to Total Capitalization Debt Instrument, Required Indebtedness to Total Capital Ratio Indebtedness to total capital ratio required to be maintained by most restrictive financial covenant. Revenue Streams [Domain] Contract with Customer, Sales Channel [Domain] Other Postretirement [Member] Other Postretirement Benefits Plan [Member] Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense [Abstract] Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract]