Fair Value Disclosures [Abstract] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Table] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Table] Fair Value, Option, Qualitative Disclosures Related to Election, by Eligible Item or Group [Axis] Fair Value, Option, Eligible Item or Group [Domain] Corporate Debt Securities [Member] Debt Securities Issued by the United States (ARS) [Member] US Treasury and Government [Member] Fair Value by Measurement Frequency [Axis] Fair Value by Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Recurring [Member] Fair Value, Measurements, Recurring [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 3 [Member] Total [Member] Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Assets [Abstract] Assets, Fair Value Disclosure [Abstract] Equity Securities Equity Method Investments, Fair Value Disclosure Available-for-sale Securities [Abstract] Available-for-sale Securities [Abstract] Available-for-sale Securities Available-for-sale Securities, Fair Value Disclosure Money Market Funds Cash and Cash Equivalents, Fair Value Disclosure Total Fair Value of Assets Assets, Fair Value Disclosure Liabilities [Abstract] Liabilities, Fair Value Disclosure [Abstract] Deferred Compensation Accrued Liabilities, Fair Value Disclosure Derivatives - Interest Rate Swap Interest Rate Cash Flow Hedge Liability at Fair Value Total Fair Value of Liabilities Liabilities, Fair Value Disclosure Total Net Fair Value of Assets (Liabilities) Net Assets and Liabilities Fair Value Disclosure This element represents the aggregate of the assets and liabilities reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. Fair Value Hierarchy Transfers, All Levels Fair Value Hierarchy Transfers, All Levels The amount of transfers in and out of levels 1, 2 and 3 of the fair value hierarchy during the period. Business Segments [Abstract] Business Segments [Abstract] Business Segments [Text Block] Segment Reporting Disclosure [Text Block] Transmission [Abstract] Transmission [Abstract] Transmission [Table] Transmission [Table] Presents detailed information about transmission investments. Transmission [Axis] Transmission [Axis] Information about each transmission investment. Transmission [Domain] Transmission [Domain] Name of transmission investment. CapX2020 Bemidji to Grand Rapids Project [Member] CapX2020 Bemidji to Grand Rapids Project [Member] Transmission investment project. CapX2020 Monticello to St. Cloud Project [Member] CapX2020 Monticello to St. Cloud Project [Member] Transmission investment project. CapX2020 Fargo to St. Cloud Project [Member] CapX2020 Fargo to St. Cloud Project [Member] Transmission investment project. CapX2020 Fargo to Monticello Projects [Member] CapX2020 Fargo to Monticello Projects [Member] Transmission investment projects. CapX2020 [Member] CapX2020 [Member] CapX2020 (all projects) [Member] Transmission [Line Items] Transmission [Line Items] Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. MPUC, Billing Factor, Approval Date MPUC, Billing Factor, Approval Date Date/expected date of approval by the Minnesota Public Utilities Commission (MPUC) of billing factor. MPUC, Updated Billing Factor, Filing Date MPUC, Updated Billing Factor, Filing Date Filing date of petition to the Minnesota Public Utilities Commission (MPUC) seeking updated billing factor approval. MPUC, Updated Billing Factor, Expected Approval Date MPUC, Updated Billing Factor, Approval Date Date/expected date of approval by the Minnesota Public Utilities Commission of updated billing factor. Number of Projects Number of Projects Number of projects. Transmission Line Length (Miles) Transmission Line Length (Miles) Length of a transmission line in miles. Transmission Line Capacity (kV) Transmission Line Capacity (kV) Capacity of a transmission line in kilovolts. Projected In Service Date In Service Date Date/expected date an asset will be in service. Project Completion Date Project Completion Date Date/expected date of project completion. Minimum Amount Expected to be Invested in Transmission Projects Minimum Amount Expected to be Invested in Transmission Projects The minimum amount expected to be invested in transmission line projects. Maximum Amount Expected to be Invested in Transmission Projects Maximum Amount Expected to be Invested in Transmission Projects The maximum amount expected to be invested in transmission line projects. Capital Cost Spent to Date Capital Cost Spent to Date Capital cost spent to date for project. MPUC, Route Permit, Approval Date MPUC, Route Permit, Approval Date Date/expected date of approval by the Minnesota Public Utilities Commission (MPUC) of route permit. Regulatory Matters [Abstract] Regulatory Matters [Abstract] Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] Regulatory Asset [Axis] Regulatory Asset [Axis] Regulatory Asset [Domain] Regulatory Asset [Domain] Deferred Fuel Costs [Member] Pension Costs [Member] Environmental Restoration Costs [Member] Deferred Income Tax Charges [Member] Asset Retirement Obligation Costs [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). CIP Financial Incentive [Member] CIP Financial Incentive [Member] CIP financial incentive [Member] Other Regulatory Assets [Member] Discloses the amount of other regulatory assets. Regulatory Liability [Axis] Regulatory Liability [Domain] Plant Removal Obligations Costs [Member] Costs provided for the removal of plant assets that are reasonably expected to be recovered in rates charged to customers. Regulatory asset or liability is recognized for differences in the timing of recognition of the period costs for financial reporting and rate-making purposes. Other Regulatory Liabilities [Member] Discloses the amount of other regulatory liabilties. Types of Rates [Axis] Information about different types of utility rates (water, gas, electric). Types Of Rates [Domain] Different types of utility rates (water, gas, electric). Water Rates [Member] Natural Gas Rates [Member] Electric Rates [Member] Unusual/Nonrecurring Items [Axis] Information about unusual/nonrecurring tax items. Unusual/Nonrecurring Items [Domain] Unusual/nonrecurring tax items. DTL Reversal, Revenue Receivable Forgone [Member] Non-recurring reversal of a deferred tax liability (DTL) related to a revenue receivable that was forgone as part of a stipulation and settlement agreement in a rate case. DTA Tax Charge, Elimination of Medicare Part D [Member] DTA Reversal, Elimination of Medicare Part D [Member] Non-recurring reversal of a deferred tax asset (DTA) related to the elimination of the tax deduction for expenses that are reimbursed under Medicare Part D. Income Tax Benefit, MPUC Approval of Deferral of PPACA [Member] Non-recurring income tax benefit related to the Minnesota Public Utilities Commission (MPUC) approval of a request to defer the retail portion of a tax charge resulting from the Patient Protection and Affordable Care Act of 2010 (PPACA). Rate Revisions [Axis] Information about periodic rate revisions. Rate Revisions [Domain] Periodic rate revisions. 2010 Rate Case [Member] Retail rate increase request filed with the Minnesota Public Utilities Commission (MPUC). FERC-Approved Wholesale Rates [Member] Wholesale rates approved by the Federal Energy Regulatory Commission (FERC). Non-Affiliated Municipal Customers, Private Utilities [Member] Non-Affiliated Municipal Customers, Private Utilities [Member] Non-Affiliated Municipal Customers, Private Utilities [Member] 2010 Wisconsin Rate Increase [Member] 2010 retail rate increase requested filed with the Public Service Commission of Wisconsin (PSCW). Regulatory Matters [Line Items] Regulatory Matters [Line Items] Regulatory Matters [Line Items] Regulatory Assets, Current Regulatory Assets, Current Regulatory Assets, Noncurrent Regulatory Assets, Noncurrent Regulatory Assets Regulatory Assets Regulatory Liability, Noncurrent Regulatory Liability, Noncurrent Original Retail Rate Increase Request Original Retail Rate Increase Request The entity's original requested amount of increase to existing rates, filed with the state regulatory commission. Interim Rate Increase Implemented Interim Rate Increase Implemented The entity's interim rate increase to existing rates, as approved by the state regulatory commission. Adjusted Retail Rate Increase Request Adjusted Retail Rate Increase Request The entity's adjusted requested amount of increase to existing rates, filed with the state regulatory commission. Requested Rate of Return on Common Equity Requested Rate of Return on Common Equity Rate of return on common equity requested by utility through a rate case proceeding filed with the state regulatory commission. Requested Percentage of Capital Structure Related to Equity Requested Percentage of Capital Structure Related to Equity The percentage of capital structure related to equity requested by utility through a rate case proceeding filed with the state regulatory commission. Requested Percentage of Capital Structure Related to Debt Requested Percentage of Capital Structure Related to Debt Percentage of capital structure related to debt requested by utility through a rate case proceeding filed with the state regulatory commission. Approved Retail Rate Increase Approved Retail Rate Increase The entity's approved amount of increase to electric rates, by the state regulatory commission. Approved Rate of Return on Common Equity Approved Rate of Return on Common Equity Rate of return on common equity approved by the state regulatory commission through a rate case proceeding. Approved Percentage of Capital Structure Related to Equity Approved Percentage of Capital Structure Related to Equity Percentage of capital structure related to equity approved by the state regulatory commission through a rate case proceeding. MPUC, Rates, Effective Date MPUC, Rates, Effective Date Effective date of established rates as approved by the Minnesota Public Utilities Commission (MPUC). Amount of Rate Differential Authorized for Collection Amount of Rate Differential Authorized for Collection The amount of differential between interim rates and final rates authorized for collection by the state regulatory commission through a rate case proceeding. Amount of Revenue Receivable Capitalized Amount of Revenue Receivable Capitalized The amount of revenue receivable capitalized, as part of rate base, as part of a stipulation and settlement agreement in a rate case. Tax Adjustments, Settlements, and Unusual Provisions Tax Adjustments, Settlements, and Unusual Provisions Non-Affiliated Municipal Customers, Municipalities Non-Affiliated Municipal Customers, Municipalities The number of municipalities that are non-affiliated municipal customers. Non-Affiliated Municipal Customers, Private Utilities Non-Affiliated Municipal Customers, Private Utilities The number of private utilities that are non-affiliated municipal customers. Length of Notice Required to Terminate (Years) Length of Notice Required to Terminate (Years) The length of notice required to terminate a contract in years. Approved Retail Rate Increase (Percent) Approved Retail Rate Increase (Percent) The entity's approved rate of increase to existing rates, by the state regulatory commission. Amount Of Estimated Additional Revenue Amount Of Estimated Additional Revenue The amount of estimated additional revenue generated on an annualized basis as a result of a rate increase. Common Stock and Earnings Per Share [Abstract] Common Stock and Earnings Per Share [Abstract] Summary of Common Stock [Table Text Block] Schedule of Stock by Class [Table Text Block] Reconciliation of Basic and Diluted Earnings Per Share [Table Text Block] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Earnings Per Share [Abstract] Antidilutive Options to Purchase Shares of Common Stock Excluded from the Computation of Earnings Per Share Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Earnings Per Share, Basic [Abstract] Earnings Per Share, Basic [Abstract] Net Income Attributable to ALLETE Net Income (Loss) Attributable to Parent Common Shares Weighted Average Number of Shares Outstanding, Basic Per Share of Common Stock Earnings Per Share, Basic Dilutive Securities (Shares) Weighted Average Number Diluted Shares Outstanding Adjustment Earnings Per Share, Diluted [Abstract] Net Income Attributable to ALLETE Net Income (Loss) Attributable to Parent, Diluted Common Shares Weighted Average Number of Shares Outstanding, Diluted Per Share of Common Stock Earnings Per Share, Diluted Pension and Other Postretirement Benefit Plans [Abstract] Pension and Other Postretirement Benefit Plans [Abstract] Pension and Other Postretirement Benefit Plan Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Axis] Pension and Other Postretirement Benefit Plans [Domain] Defined Benefit Plans and Other Postretirement Benefit Plans [Domain] Pension [Member] Pension Plans, Defined Benefit [Member] Postretirement Health and Life [Member] Other Postretirement Benefit Plans, Defined Benefit [Member] VEBA [Member] VEBA (Voluntary Employee Benefits Association trusts) [Member] Grantor Trust [Member] Irrevocable Grantor Trusts [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Pension and Other Postretirement Benefit Contributions Stock Issued During Period, Value, Employee Benefit Plan Stock Issued During Period, Value, Employee Benefit Plan Contributions by Employer through ESOP Defined Benefit Plan, Contributions by Employer through ESOP Defined Benefit Plan, Contributions by Employer through ESOP Estimated Employer Contributions in Next Fiscal Year Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year Employee Stock and Incentive Plans [Abstract] Employee Stock and Incentive Plans [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangement by Share-based Payment Award, Award Type and Plan Name [Axis] Share-based Compensation Arrangements by Share-based Payment Award, Award Type and Plan Name [Domain] Restricted Stock Units (RSUs) [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Number of Shares [Abstract] Number of Shares [Abstract] Available as of January 1, Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Granted Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Awarded Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Awards, Shares Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Awards, Shares Forfeited Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Available as of December 31, Weighted Average Grant Date Fair Value [Abstract] Weighted Average Grant Date Fair Value [Abstract] As of January 1, Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Granted Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Awarded Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Awards, Weighted Average Grant Date Fair Value (Per Share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Awards, Weighted Average Grant Date Fair Value (Per Share) Forfeited Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period, Weighted Average Grant Date Fair Value As of December 31, Restricted Stock Units Granted, Grant Date Fair Value Restricted Stock Units Granted, Grant Date Fair Value Restricted Stock Units Granted, Grant Date Fair Value Total Restricted Stock Units Awarded, Shares Restricted Stock Units Awarded, Shares Restricted Stock Units Awarded, Shares Restricted Stock Units Awarded, Grant Date Fair Value Restricted Stock Units Awarded, Grant Date Fair Value Income Tax Disclosure [Abstract] Current Federal Tax Expense (Benefit) Current State Tax Expense (Benefit) Current State and Local Tax Expense (Benefit) Total Current Tax Expense (Benefit) Current Income Tax Expense (Benefit) Deferred Federal Tax Expense (Benefit) Deferred Federal Income Tax Expense (Benefit) Deferred State Tax Expense (Benefit) Deferred State and Local Income Tax Expense (Benefit) Change in Valuation Allowance Valuation Allowance, Deferred Tax Asset, Change in Amount Investment Tax Credit Amortization Deferred Other Tax Expense (Benefit) Total Deferred Tax Expense Deferred Income Tax Expense (Benefit) Total Income Tax Expense Income Tax Expense (Benefit) Income Tax Expense Nonrecurring Items [Table] Income Tax Expense Nonrecurring Items [Table] Income Tax Expense Nonrecurring Items [Table] Unusual or Infrequent Item [Axis] Unusual or Infrequent Item [Domain] Income Tax Benefit, MPUC Approval of Deferral of PPACA [Member] DTL Reversal, Revenue Receivable Forgone [Member] Income Tax Contingency [Line Items] Income Tax Contingency [Line Items] Unusual or Infrequent Item [Axis] Unusual or Infrequent Item [Domain] Unusual or Infrequent Item [Line Items] Unusual or Infrequent Item [Line Items] Income Before Non-Controlling Interest and Income Taxes Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest Statutory Federal Income Tax Rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate Income Taxes Computed at 35 Percent Statutory Federal Rate Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate State Income Taxes - Net of Federal Income Tax Benefit Income Tax Reconciliation, State and Local Income Taxes Regulatory Differences for Utility Plant Effective Income Tax Rate Reconciliation, Regulatory Differences Regulatory Differences contributing to difference in effective tax rate to federal statutory rate. Production Tax Credit Income Tax Reconciliation, Tax Credits, Other Other Income Tax Reconciliation, Other Adjustments Income Tax Expense Effective Income Tax Rate Effective Income Tax Rate, Continuing Operations Fair Value [Text Block] Fair Value Disclosures [Text Block] Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] Long-Term Debt, Including Current Portion - Carrying Amount Long-term Debt Long-Term Debt, Including Current Portion - Fair Value Long-term Debt, Fair Value Employee Stock Ownership Plan [Table Text Block] Schedule of Employee Stock Ownership Plan (ESOP) Disclosures [Table Text Block] Share-Based Compensation Expense [Table Text Block] Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block] Non-Qualified Stock Options [Table Text Block] Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block] Stock Options, by Exercise Price Range [Table Text Block] Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block] Non-Vested Performance Shares [Table Text Block] Schedule of Nonvested Performance-based Units Activity [Table Text Block] Restricted Stock Units [Table Text Block] Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block] Other Matters [Abstract] Other Matters [Abstract] Loss Contingencies [Table] Loss Contingencies [Table] Loss Contingencies by Nature of Contingency [Axis] Loss Contingencies by Nature of Contingency [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Pending or Threatened Litigation [Member] Pending or Threatened Litigation [Member] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Loss Contingency, Damages Sought, Value Loss Contingency, Damages Sought, Value Accumulated Other Comprehensive Income (Loss) [Abstract] Accumulated Other Comprehensive Income (Loss) [Abstract] Unrealized Loss on Securities Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Unrealized Loss on Derivatives Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax Defined Benefit Pension and Other Postretirement Plans Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax Total Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Income (Loss), Net of Tax Comprehensive Income (Loss) [Abstract] Comprehensive Income (Loss) [Abstract] Net Income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Other Comprehensive Income (Loss) [Abstract] Other Comprehensive Income (Loss) [Abstract] Unrealized Gain (Loss) on Securities Net of income taxes of $(0.1), $0.6, and $1.7 Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Unrealized Loss on Derivatives Net of income taxes of $(0.2) $-, and $- Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Defined Benefit Pension and Other Postretirement Plans Net of income taxes of $(3.6), $-, and $4.1 Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Total Other Comprehensive Income (Loss) Other Comprehensive Income (Loss), Net of Tax Total Comprehensive Income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Less: Non-Controlling Interest in Subsidiaries Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Comprehensive Income Attributable to ALLETE Comprehensive Income (Loss), Net of Tax, Attributable to Parent Unrealized Gain (Loss) on Securities, Income Taxes Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax Unrealized Loss on Derivatives, Income Taxes Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax Defined Benefit Pension and Other Postretirement Plans, Income Taxes Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Tax Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Projected Benefit Obligation Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Projected Benefit Obligation Accumulated Benefit Obligation Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Accumulated Benefit Obligation Fair Value of Plan Assets Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets Obligation and Funded Status [Table Text Block] Schedule of Net Funded Status [Table Text Block] Unrecognized Pension and Other Postretirement Costs [Table Text Block] Unrecognized Pension Costs [Table Text Block] The components of unrecognized pension and other postretirement benefit cost, including net loss, prior service costs [Table Text Block] Components of Net Periodic Expense [Table Text Block] Schedule of Net Benefit Costs [Table Text Block] Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income and Regulatory Assets [Table Text Block] Schedule of Amounts Recognized in Other Comprehensive Income and Regulatory Assets [Table Text Block] Schedule of Pension Amounts Recognized in Other Comprehensive Income and Regulatory Assets [Table Text Block] Information for Pension Plans with an Accumulated Benefit Obligation in Excess of Plan Assets [Table Text Block] Schedule of Accumulated Benefit Obligations in Excess of Fair Value of Plan Assets [Table Text Block] Estimated Future Benefit Payments [Table Text Block] Schedule of Expected Benefit Payments [Table Text Block] Pension and Postretirement Health and Life Costs Recorded in Other Long-Term Assets and Accumulated Other Comprehensive Income Expected to be Recognized over the Next Fiscal Year [Table Text Block] Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year [Table Text Block] Weighted-Average Assumptions Used to Determine Benefit Obligation and Net Periodic Benefit Costs [Table Text Block] Schedule of Assumptions Used [Table Text Block] Sensitivity of a One-Percentage-Point Change in Health Care Trend Rates [Table Text Block] Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block] Actual Plan Asset Allocations [Table Text Block] Actual Plan Asset Allocations [Table Text Block] Actual Plan Asset Allocations [Table Text Block] Plan Asset Target Allocations [Table Text Block] Schedule of Allocation of Plan Assets [Table Text Block] Recurring Fair Value Measures [Table Text Block] Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Activity in Level 3 [Table Text Block] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Number of Options [Abstract] Number of Options [Abstract] Outstanding as of January 1, Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Granted Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures Exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Forfeited Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period Outstanding as of December 31, Exercisable as of December 31, Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Weighted Average Exercise Price [Abstract] Weighted Average Exercise Price [Abstract] Outstanding as of January 1, Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Granted Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Forfeited Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Outstanding as of December 31, Exercisable as of December 31, Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Proceeds from Stock Options Exercised Weighted Average Grant Date Intrinsic Value of Options Granted Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Grant Date Intrinsic Value Total Intrinsic Value of Options Exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value Power Purchase Agreements [Abstract] -- None. No documentation exists for this element. -- Power Purchase Agreements [Table] Long-term Purchase Commitment [Table] North Dakota Wind Development [Axis] North Dakota Wind Development [Axis] Information about each wind project/transmission line in North Dakota. North Dakota Wind Development [Domain] North Dakota Wind Development [Domain] Name of wind project/transmission line in North Dakota. DC Transmission Line from Square Butte [Member] DC Transmission Line from Square Butte [Member] Transmission line purchased as part of North Dakota Wind Development projects. Power Purchase Agreements [Axis] Long-term Contract for Purchase of Electric Power [Axis] Power Purchase Agreements [Domain] Long-term Contract for Purchase of Electric Power [Domain] Minnkota Power Sales Agreement [Member] Minnkota Power Sales Agreement [Member] Long-term contract with Minnkota Power for the purchase of electric power. 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. 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. Oliver Wind I and II PPA [Member] Oliver Wind I and II PPA [Member] Long-term contracts with an affiliate of NextEra Energy, Inc. for the purchase of electric power. Manitoba Hydro PPA (expires April 2015) [Member] Manitoba Hydro PPA (expires April 2015) [Member] Long-term contract with Manitoba Hydro for the purchase of electric power. Manitoba Hydro PPA (expires April 2022) [Member] Manitoba Hydro PPA (expires April 2022) [Member] Long-term contract with Manitoba Hydro for the purchase of electric power. Manitoba Hydro PPA (expires 2035) [Member] Manitoba Hydro PPA (expires 2035) [Member] Manitoba Hydro PPA (expires 2035) [Member] Square Butte PPA [Member] Square Butte PPA [Member] Long-term contract with Square Butte for the purchase of electric power. Power Purchase Agreements [Line Items] Long-term Purchase Commitment [Line Items] Transmission Line Purchase Date Transmission Line Purchase Date Date of purchase of a transmission line. Long Term Contract For Purchase Of Electric Power Date Agreement Was Executed Long Term Contract For Purchase Of Electric Power Date Agreement Was Executed Date agreement of long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization was executed. Long-term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased (MW) Long-term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased (MW) Share of plant output being purchased in megawatts under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. 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. fixed capacity charge fixed capacity charge Fixed capacity charge under PPA. Long-term Contract for Purchase of Electric Power, Start Date of Contract Long-term Contract for Purchase of Electric Power, Start Date of Contract Start date of long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. Long-term Contract for Purchase of Electric Power, Number of Wind PPAs Long-term Contract for Purchase of Electric Power, Number of Wind PPAs Number of long-term wind contracts to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. Cost of Purchased Power Cost of Purchased Power Long-term Contract for Purchase of Electric Power, Date of Contract Expiration Long-Term Contract for Purchase of Electric Power, Date of Contract Expiration, Duration String Long-Term Contract for Purchase of Electric Power, Date of Contract Expiration, Duration String Long-term Contract for Purchase of Electric Power, Anticipated Date of New Transmission Line Long-term Contract for Purchase of Electric Power, Anticipated Date of New Transmission Line Anticipated date that a new transmission line will be built as part of a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. Long-term Contract for Purchase of Electric Power, Generating Unit Capacity (MW) Long-term Contract for Purchase of Electric Power, Generating Unit Capacity (MW) The generating capacity of a production plant constructed and financed by a public utility district, cooperative, or other organization with whom exists a long-term contract to purchase electric power. Long-term Contract for Purchase of Electric Power, Amount of Long-term Debt or Lease Obligation Outstanding Long-term Contract for Purchase of Electric Power, Amount of Long-term Debt or Lease Obligation Outstanding Long-term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased Long-term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased Long-term Contract for Purchase of Electric Power, Annual Minimum Debt Service Payment Required Long-term Contract for Purchase of Electric Power, Annual Minimum Debt Service Payment Required Interest Expense Interest Expense Long-term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased (MWh) Long-term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased (MWh) Share of plant output being purchased in megawatthours under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. Long-term Contract for Purchase of Electric Power, Date of MPUC Approval Long-term Contract for Purchase of Electric Power, Date of MPUC Approval Date of approval by Minnesota Public Utilities Commission (MPUC) of long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. Fair Value Transfers [Policy Text Block] Fair Value Transfer, Policy [Policy Text Block] Regulatory Assets and Liabilities [Policy Text Block] Public Utilities, Policy [Policy Text Block] Other Income and Expenses [Abstract] Other Income (Expense) [Table Text Block] Schedule of Other Nonoperating Income (Expense) [Table Text Block] Investments [Abstract] Long-term Contracts for Purchase of Electric Power [Table] Long-term Contract for Purchase of Electric Power [Line Items] Output Purchased (Percent) Output Purchased (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 Real Estate Sales Revenue Recognition, Minimum Contract Price Cash Collections Requirement The minimum amount of cash collected on the contract price in order to fully recognize profit on the sale of real estate upon closing (company policy). Property, Plant and Equipment [Abstract] Property, Plant and Equipment [Text Block] Property, Plant and Equipment Disclosure [Text Block] Recurring Fair Value Measures, Activity in Level 3 [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value by Asset Class [Axis] Fair Value by Asset Class [Axis] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, by Asset Class [Domain] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, by Asset Class [Domain] Derivatives [Member] Derivative Financial Instruments, Assets [Member] Debt Securities Issued by States of the United States (ARS) [Member] Recurring Fair Value Measures, Activity in Level 3 [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Beginning Balance Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Settled During the Period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements Redeemed During the Period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales Ending Balance Coal Rail and Shipping Contracts [Abstract] Coal Rail and Shipping Contracts [Abstract] Coal Rail and Shipping Contracts [Table] Recorded Unconditional Purchase Obligation [Table] Coal Rail and Shipping Contracts [Axis] Recorded Unconditional Purchase Obligation by Category of Item Purchased [Axis] Coal Rail and Shipping Contracts [Domain] Unconditional Purchase Obligation, Category of Goods or Services Acquired [Domain] Public Utilities, Inventory, Coal [Member] Public Utilities, Inventory, Coal [Member] Coal Rail and Shipping Contracts [Line Items] Recorded Unconditional Purchase Obligation [Line Items] Recorded Unconditional Purchase Obligation Due within One Year Recorded Unconditional Purchase Obligation Due within One Year Recorded Unconditional Purchase Obligation Due in Second Year Recorded Unconditional Purchase Obligation Due in Second Year Statement of Cash Flows [Abstract] Operating Activities Net Cash Provided by (Used in) Operating Activities [Abstract] Allowance for Funds Used During Construction Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity Loss (Income) from Equity Investments, Net of Dividends Income (Loss) from Equity Method Investments, Net of Dividends or Distributions Gain on Real Estate Foreclosure Gain On Real Estate Foreclosure Gain On Real Estate Foreclosure Gain on Sale of Assets Gain (Loss) on Sale of Other Assets Loss on Impairment of Assets Asset Impairment Charges Depreciation Expense Depreciation Amortization of Debt Issuance Costs Debt Related Commitment Fees and Debt Issuance Costs Deferred Income Tax Expense Share-Based Compensation Expense Share-based Compensation ESOP Compensation Expense Employee Stock Ownership Plan (ESOP), Compensation Expense Defined Benefit Pension and Postretirement Benefit Expense Pension and Other Postretirement Benefit Expense Bad Debt Expense Provision for Doubtful Accounts Changes in Operating Assets and Liabilities Increase (Decrease) in Operating Capital [Abstract] Accounts Receivable Increase (Decrease) in Accounts and Other Receivables Inventories Increase (Decrease) in Inventories Prepayments and Other Increase (Decrease) in Prepaid Expense and Other Assets Accounts Payable Increase (Decrease) in Accounts Payable Other Current Liabilities Increase Decrease In Operating Liabilities Current The net change during the reporting period in other current operating liabilities not otherwise defined in the taxonomy Cash Contributions to Defined Benefit Pension and Postretirement Plans Increase (Decrease) in Pension and Postretirement Obligations Changes in Regulatory and Other Non-Current Assets Increase (Decrease) in Other Operating Assets Changes in Regulatory and Other Non-Current Liabilities Increase (Decrease) in Other Operating Liabilities Cash from Operating Activities Net Cash Provided by (Used in) Operating Activities Investing Activities Net Cash Provided by (Used in) Investing Activities [Abstract] Proceeds from Sale of Available-for-sale Securities Proceeds from Sale of Available-for-sale Securities Payments for Purchase of Available-for-sale Securities Payments to Acquire Available-for-sale Securities Investment in ATC Investment In Subsidiary Cash out for additional investment in subsidiary Changes to Other Investments Payments for (Proceeds from) Other Investing Activities Additions to Property, Plant and Equipment Payments to Acquire Property, Plant, and Equipment Proceeds from Sale of Assets Proceeds from Sale of Productive Assets Cash for Investing Activities Net Cash Provided by (Used in) Investing Activities Financing Activities Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from Issuance of Common Stock Proceeds from Issuance of Common Stock Proceeds from Issuance of Long-Term Debt Proceeds from Issuance of Long-term Debt Changes in Notes Payable Proceeds from (Repayments of) Notes Payable Reductions of Long-Term Debt Repayments of Long-term Debt Debt Issuance Costs Payments of Debt Issuance Costs Dividends on Common Stock Payments of Dividends, Common Stock Cash from Financing Activities Net Cash Provided by (Used in) Financing Activities Change in Cash and Cash Equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and Cash Equivalents at Beginning of Period Cash and Cash Equivalents, at Carrying Value Cash and Cash Equivalents at End of Period Effect of One Percent Increase on Total of Postretirement Health and Life Service and Interest Cost Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components Effect of One Percent Decrease on Total of Postretirement Health and Life Service and Interest Cost Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components Effect of One Percent Increase on Postretirement Health and Life Obligation Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation Effect of One Percent Decrease on Postretirement Health and Life Obligation Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation Common Stock and Earnings Per Share [Text Block] Earnings Per Share [Text Block] North Dakota Wind Development [Abstract] North Dakota Wind Development [Abstract] North Dakota Wind Development [Table] North Dakota Wind Development [Table] Presents detailed information about wind development projects in North Dakota. Bison 1 Wind Project [Member] Bison 1 Wind Project [Member] Wind project in North Dakota. Bison 1 Wind Project, Phase 1 [Member] Bison 1 Wind Project, Phase 1 [Member] Phase of wind project in North Dakota. Bison 1 Wind Project, Phase 2 [Member] Bison 1 Wind Project, Phase 2 [Member] Phase of wind project in North Dakota. Bison 2 and 3 Wind Projects [Member] Bison 2 and 3 Wind Projects [Member] Wind projects in North Dakota. Bison 2 Wind Project [Member] Bison 2 Wind Project [Member] Wind project in North Dakota. Bison 3 Wind Project [Member] Bison 3 Wind Project [Member] Wind project in North Dakota. North Dakota Wind Development [Line Items] North Dakota Wind Development [Line Items] Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Generating Unit Capacity (MW) Generating Unit Capacity (MW) Capacity of each generating unit/individual project in megawatts. Number of Turbines Number of Turbines Number of turbines at a site. Capacity of Turbines (MW) Capacity of Turbines (MW) Capacity of each turbine in megawatts at a site. Expected Capital Cost Expected Capital Cost Expected capital cost for each individual project. MPUC, Current Cost Recovery, Approval Date MPUC, Current Cost Recovery, Approval Date Date/expected date of approval by the Minnesota Public Utilities Commission (MPUC) of current cost recovery for expenditures and investments related to a project. MPUC, Rates, Approval Date MPUC, Rates, Approval Date Date/expected date of approval by the Minnesota Public Utilities Commission (MPUC) establishing rates. MPUC Updated Approval Date MPUCUpdatedApprovalDate MPUCUpdatedApprovalDate MPUC, Project, Approval Date MPUC, Project, Approval Date Date/expected date of project approval by the Minnesota Public Utilities Commission (MPUC). NDPSC, Site Permit, Approval Date NDPSC, Site Permit, Approval Date Date/expected date of approval of site permit by the North Dakota Public Service Commission (NDPSC). Long-term Debt, Current and Noncurrent [Abstract] Long-term Debt [Table Text Block] Schedule of Long-term Debt Instruments [Table Text Block] Comprehensive Income (Loss) [Table Text Block] Schedule of Comprehensive Income (Loss) [Table Text Block] Accumulated Other Comprehensive Income (Loss) [Table Text Block] Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Other Investments and ALLETE Properties [Table Text Block] Investment [Table Text Block] Available-for-sale Securities Reconciliation [Table Text Block] Schedule of Available-for-sale Securities Reconciliation [Table Text Block] Available-for-sale Securities [Table Text Block] Regulatory Assets and Liabilities [Text Block] Schedule of Regulatory Assets and Liabilities [Text Block] Income Tax Expense [Table Text Block] Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] 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] Deferred Tax Assets and Liabilities [Table Text Block] Schedule of Deferred Tax Assets and Liabilities [Table Text Block] NOL and Tax Credit Carryforwards [Table Text Block] Summary of Operating Loss and Tax Credit Carryforwards [Table Text Block] Summary of Operating Loss and Tax Credit Carryforwards [Table Text Block] [Table Text Block] Gross Unrecognized Income Tax Benefits [Table Text Block] Summary of Income Tax Contingencies [Table Text Block] Investment in ATC [Abstract] Investment in ATC [Abstract] Investment in ATC [Text Block] Equity Method Investments Disclosure [Text Block] Income Statement [Abstract] Net Income Net Income (Loss) Available to Common Stockholders, Basic [Abstract] Operating Revenue Revenues [Abstract] Operating Revenue Regulated and Unregulated Operating Revenue Prior Year Rate Refunds Customer Refundable Fees, Refund Payments Total Operating Revenue Total Operating Revenue Operating Expenses Cost of Revenue [Abstract] Fuel and Purchased Power Cost of Domestic Regulated Electric Operating and Maintenance Utilities Operating Expense, Maintenance and Operations Depreciation Utilities Operating Expense, Depreciation and Amortization Total Operating Expenses Utilities Operating Expense Operating Income Operating Income (Loss) Other Income (Expense) Nonoperating Income (Expense) [Abstract] Interest Expense Equity Earnings in ATC Income (Loss) from Equity Method Investments Other Other Nonoperating Income (Expense) Total Other Expense Nonoperating Income (Expense) Income Before Non-Controlling Interest and Income Taxes Income Loss From Continuing Operations Before Income Taxes Minority Interest Net Income Less: Non-Controlling Interest in Subsidiaries Net Income (Loss) Attributable to Noncontrolling Interest Net Income Attributable to ALLETE Average Shares of Common Stock Basic (in shares) Diluted (in shares) Basic Earnings Per Share of Common Stock Diluted Earnings Per Share of Common Stock Dividends Per Share of Common Stock (in dollars per share) Common Stock, Dividends, Per Share, Declared Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward] Land Inventory Beginning Balance Land Available-for-sale Deeds to Collateralized Property Real Estate, Acquisitions Through Foreclosures Land Impairment Other than Temporary Impairment Losses, Investments Cost of Real Estate Sold Real Estate, Cost of Real Estate Sold Capitalized Improvements and Other Real Estate, Improvements Land Inventory Ending Balance Long-Term Finance Receivables (net of allowances of $0.6 and $0.8) Loans and Leases Receivable, Net Reported Amount Other Other Real Estate Total Real Estate Assets Real Estate, Gross Long-Term Finance Receivable Allowance Allowance for Notes, Loans and Financing Receivable, Noncurrent ALLETE Properties Available-for-sale Securities Available-for-sale Securities, Noncurrent Other Other Long-term Investments Total Investments Long-term Investments Cost Available-for-sale Securities, Amortized Cost Basis Gross Unrealized Gain Available-for-sale Securities, Gross Unrealized Gains Gross Unrealized (Loss) Available-for-sale Securities, Gross Unrealized Losses Fair Value Net Proceeds Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds Gross Realized Gain Available-for-sale Securities, Gross Realized Gains Gross Realized (Loss) Available-for-sale Securities, Gross Realized Losses Net Unrealized Gain (Loss) in Other Comprehensive Income Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax Available for sale securities, Issued by States of the United States (ARS) Total of debt securities issued by states of the United States categorized as neither held-to-maturity nor trading. Notes, Loans and Financing Receivable, Net, Noncurrent [Abstract] Notes, Loans and Financing Receivable, Net, Noncurrent Financing Receivable, Allowance for Credit Losses, Provisions Operations and Significant Accounting Policies [Abstract] Operations and Significant Accounting Policies [Abstract] Operations and Significant Accounting Policies [Text Block] Significant Accounting Policies [Text Block] Jointly-Owned Electric Facility [Abstract] Jointly-Owned Electric Facility [Abstract] Jointly Owned Electric Facility [Table Text Block] Schedule of Jointly Owned Utility Plants [Table Text Block] Plan Asset Categories [Axis] Defined Benefit Plan by Plan Asset Categories [Axis] Plan Asset Categories [Domain] Equity Securities [Member] Debt Securities [Member] Real Estate [Member] Private Equity [Member] Private Equity Funds [Member] Actual Plan Asset Allocations [Abstract] Defined Benefit Plan, Actual Plan Asset Allocations [Abstract] Actual Plan Asset Allocation Defined Benefit Plan, Actual Plan Asset Allocations Plan Asset Target Allocations [Abstract] Defined Benefit Plan, Assets, Target Allocations [Abstract] Equity Securities Target Allocation Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities Debt Securities Target Allocation Defined Benefit Plan, Target Allocation Percentage of Assets, Debt Securities Real Estate Target Allocation Defined Benefit Plan, Target Allocation Percentage of Assets, Real Estate Private Equity Target Allocation Defined Benefit Plan, Target Allocation Percentage of Assets, Other ALLETE Common Stock Included in Pension Plan Equity Securities Defined Benefit Plan, Number of Shares of Equity Securities Issued by Employer and Related Parties Included in Plan Assets Stock Issued During Period, Shares, Employee Benefit Plan Stock Issued During Period, Shares, Employee Benefit Plan Recurring Fair Value Measures Activity in Level 3 [Table Text Block] Financial Instruments [Table Text Block] Fair Value, by Balance Sheet Grouping [Table Text Block] Public Utility, Property, Plant and Equipment [Table] Property, Plant and Equipment by Regulated or Unregulated Status [Axis] Public Utility Regulated or Unregulated Status [Axis] Property, Plant and Equipment Regulated and Unregulated Operation [Domain] Regulated and Unregulated Operation [Domain] Regulated Utiity [Member] Regulated Operation [Member] Unregulated Non-Rate Base Energy Operations and Other Plant [Member] Unregulated Operation [Member] Property, Plant and Equipment [Line Items] Segment Property, Plant and Equipment Public Utilities, Property, Plant and Equipment, Plant in Service Construction Work in Progress Public Utilities, Property, Plant and Equipment, Construction Work in Progress Accumulated Depreciation Public Utilities, Property, Plant and Equipment, Accumulated Depreciation Segment Property, Plant and Equipment - Net Public Utilities, Property, Plant and Equipment, Net Other Plant - Net Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment Property, Plant and Equipment - Net Property, Plant and Equipment, Net Estimated Useful Life - Generation Public Utilities, Property, Plant and Equipment, Generation, Estimated Useful Life Estimated Useful Life - Transmission Public Utilities, Property, Plant and Equipment, Transmission, Estimated Useful Life Estimated Useful Life - Distribution Public Utilities, Property, Plant and Equipment, Distribution, Estimated Useful Life Estimated Useful Life - Non-Rate Base Operations Public Utilities, Property, Plant and Equipment, Common, Estimated Useful Life Estimated Useful Life - Other Plant Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Estimated Useful Life Asset Retirement Obligation [Roll Forward] Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] Beginning Obligation Asset Retirement Obligation Accretion Expense Asset Retirement Obligation, Accretion Expense Additional Liabilities Incurred Asset Retirement Obligation, Liabilities Incurred Ending Obligation Net Loss Defined Benefit Plan, Amortization of Net Gains (Losses) Prior Service Costs Defined Benefit Plan, Amortization of Net Prior Service Cost (Credit) Transition Obligations Defined Benefit Plan, Amortization of Net Transition Asset (Obligation) Total Pension and Postretirement Health and Life Costs Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year Net Loss Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax Prior Service Cost Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax Transition Obligation Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Transition Assets (Obligations), before Tax Total Unrecognized Costs Executive Option and Incentive Plans [Policy Text Block] Stock-Based Compensation, Executive Option and Incentive Plans [Policy Text Block] Stock-Based Compensation, Executive Option and Incentive Plans [Policy Text Block] Employee Stock Ownership Plan [Policy Text Block] Employee Stock Ownership Plan (ESOP), Policy [Policy Text Block] Performance Shares, RSU's, ESPP, and RSOP [Policy Text Block] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Policy [Policy Text Block] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Policy [Policy Text Block] ESOP Employer Loan, Description Employee Stock Ownership Plan (ESOP), Debt Structure, Employer Loan, Description Allocated Employee Stock Ownership Plan (ESOP), Number of Allocated Shares Unallocated Employee Stock Ownership Plan (ESOP), Number of Suspense Shares Total Employee Stock Ownership Plan (ESOP), Shares in ESOP Fair Value of Unallocated Shares Employee Stock Ownership Plan (ESOP), Deferred Shares, Fair Value Leasing Agreements [Abstract] Leasing Agreements [Abstract] Leasing Agreements [Table] Schedule of Operating Leased Assets [Table] Leasing Agreements by Type [Axis] Property, Plant and Equipment by Type [Axis] Leasing Agreements, Type [Domain] Property, Plant and Equipment, Type [Domain] Exploration and Production Equipment [Member] Exploration and Production Equipment [Member] Leasing Agreements [Line Items] Operating Leased Assets [Line Items] Annual Lease Payment Annual Lease Payment Annual payment for operating lease agreement. Leasing Agreement Expiration Date Leasing Agreement Expiration Date Expiration date of operating lease agreement. Termination Fee Termination Fee A lump sum payment in conjunction with a lease termination. Operating Leases, Future Minimum Payments Due, Current Operating Leases, Future Minimum Payments Due, Current Operating Leases, Future Minimum Payments, Due in Two Years Operating Leases, Future Minimum Payments, Due in Two Years Operating Leases, Future Minimum Payments, Due in Three Years Operating Leases, Future Minimum Payments, Due in Three Years Operating Leases, Future Minimum Payments, Due in Four Years Operating Leases, Future Minimum Payments, Due in Four Years Operating Leases, Future Minimum Payments, Due in Five Years Operating Leases, Future Minimum Payments, Due in Five Years Operating Leases, Future Minimum Payments, Due Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Operating Leases, Rent Expense Operating Leases, Rent Expense Guarantor Obligations [Table] Schedule of Guarantor Obligations [Table] Guarantor Obligations by Nature [Axis] Guarantor Obligations by Nature [Axis] Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] BNI Coal Reclamation Liability [Member] BNI Coal Reclamation Liability [Member] Reclamation liability for closing costs associated with BNI Coal mine and mine facilities. ALLETE Properties Performance and Maintenance Obligations [Member] ALLETE Properties Performance and Maintenance Obligations [Member] Performance and maintenance obligations to governmental entities to construct improvements in various projects. Town Center Community Development District [Member] Town Center Community Development District [Member] Community development district obligations for Town Center District. Palm Coast Park Community Development District [Member] Palm Coast Park Community Development District [Member] Community development district obligations for Palm Coast Park District. Community Development Districts [Member] Community Development Districts [Member] Community development district obligations. Guarantor Obligations [Line Items] Guarantor Obligations [Line Items] Surety Bonds Outstanding Surety Bonds Outstanding Amount of surety bonds that are available for future payment obligations. Performance and Maintenance Obligations Performance and Maintenance Obligations Estimated costs remaining on performance and maintenance obligations. Total amount of letter of credit secured in addition to surety bonds for reclamation liability Total amount of letter of credit secured in addition to surety bonds for reclamation liability Amount of letter of credit issued in addition to surety bond to secure performance obligation. Total current estimated reclamation liability Total current estimated reclamation liability Total current estimated liability for performance obligation. Capital Improvement Revenue/Special Assessment Bonds, Date Issued Capital Improvement Revenue/Special Assessment Bonds, Date Issued Issue date of municipal bonds used to fund a development project. Special Assessment Bond Special Assessment Bond Capital Improvement Revenue/Special Assessment Bonds, Interest Rate Capital Improvement Revenue/Special Assessment Bonds, Interest Rate Interest rate of municipal bonds used to fund a development project. Capital Improvement Revenue/Special Assessment Bonds, Term (Years) Capital Improvement Revenue/Special Assessment Bonds, Term (Years) Term in years of municipal bonds used to fund a development project. Capital Improvement Revenue/Special Assessment Bonds, Ownership Percentage of Benefited Property Capital Improvement Revenue/Special Assessment Bonds, Ownership Percentage of Benefited Property Ownership percentage of property benefited by a development project funded by municipal bonds. Capital Improvement Revenue/Special Assessment Bonds, Annual Assessments Based on Ownership Percentage Capital Improvement Revenue/Special Assessment Bonds, Annual Assessments Based on Ownership Percentage Annual assessments based on ownership percentage of property benefited by a development project funded by municipal bonds. Equity Method Investment, Expected Future Investment Equity Method Investment, Expected Future Investment Equity Method Investment - Additional Investment Amount Equity Method Investment - Additional Investment Amount 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. Equity Method Investment, Ownership Percentage ALLETE's Investment in ATC [Roll Forward] ALLETE's Investment in ATC [Roll Forward] Equity Investment Beginning Balance Equity Method Investments Cash Investments Payments to Acquire Businesses and Interest in Affiliates Distributed ATC Earnings Equity Method Investment, Dividends or Distributions Equity Investment Ending Balance ATC Summarized Financial Data [Abstract] ATC Summarized Financial Data [Abstract] Balance Sheet Data [Abstract] Equity Method Investment Summarized Financial Information Balance Sheet [Abstract] Equity Method Investment Summarized Financial Information Balance Sheet [Abstract] Current Assets Equity Method Investment, Summarized Financial Information, Current Assets Non-Current Assets Equity Method Investment, Summarized Financial Information, Noncurrent Assets Total Assets Equity Method Investment, Summarized Financial Information, Assets Current Liabilities Equity Method Investment, Summarized Financial Information, Current Liabilities Long-Term Debt Equity Method Investment, Summarized Financial Information, Long-Term Debt Equity Method Investment, Summarized Financial Information, Long-Term Debt Other Non-Current Liabilities Equity Method Investment, Summarized Financial Information, Other Non-Current Liabilities Equity Method Investment, Summarized Financial Information, Other Non-Current Liabilities Members' Equity Equity Method Investment Summarized Financial Information, Equity Total Liabilities and Members' Equity Equity Method Investment, Summarized Financial Information, Liabilities and Equity Income Statement Data [Abstract] Equity Method Investment, Summarized Financial Information, Income Statement [Abstract] Revenue Equity Method Investment, Summarized Financial Information, Revenue 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. Other Expense Equity Method Investment, Summarized Financial Information, Other Expense The amount of other expense reported by an equity method investment of the entity. Net Income Equity Method Investment, Summarized Financial Information, Net Income (Loss) ALLETE's Equity in Net Income Debt Disclosure [Abstract] Short-Term and Long-Term Debt [Text Block] Debt Disclosure [Text Block] Other Income (Expense) [Text Block] Other Income and Other Expense Disclosure [Text Block] Schedule II [Abstract] Schedule II [Abstract] Valuation and Qualifying Accounts and Reserves [Table] Valuation and Qualifying Accounts Disclosure [Table] Valuation Allowances and Reserves Type [Axis] Valuation Allowances and Reserves Type [Axis] Valuation Allowances and Reserves [Domain] Valuation Allowances and Reserves [Domain] Trade Accounts Receivable [Member] Allowance for Trade Receivables [Member] Finance Receivables - Long-Term [Member] Allowance for Losses on Finance Receivables [Member] Deferred Tax Assets [Member] Valuation Allowance of Deferred Tax Assets [Member] Valuation and Qualifying Accounts and Reserves [Line Items] Valuation and Qualifying Accounts Disclosure [Line Items] Balance at Beginning of Period Valuation Allowances and Reserves, Balance Additions, Charged to Income Valuation Allowances and Reserves, Charged to Cost and Expense Additions, Other Charges Valuation Allowances and Reserves, Charged to Other Accounts Deductions from Reserves Valuation Allowances and Reserves, Deductions Balance at End of Period Short-Term and Long-Term Debt [Abstract] SHORT-TERM AND LONG-TERM DEBT [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] 4.86% Series Due 2013 [Member] First Mortgage Bonds, 4.86% Series Due 2013 [Member] 6.94% Series Due 2014 [Member] First Mortgage Bonds, 6.94% Series Due 2014 [Member] 7.70% Series Due 2016 [Member] First Mortgage Bonds, 7.70% Series Due 2016 [Member] 8.17% Series Due 2019 [Member] First Mortgage Bonds, 8.17% Series Due 2019 [Member] 5.28% Series Due 2020 [Member] First Mortgage Bonds, 5.28% Series Due 2020 [Member] 4.85% Series Due 2021 [Member] First Mortgage Bonds, 4.85% Series Due 2021 [Member] 4.95% Pollution Control Series F Due 2022 [Member] First Mortgage Bonds, 4.95% Pollution Control Series F Due 2022 [Member] 6.02% Series Due 2023 [Member] First Mortgage Bonds, 6.02% Series Due 2023 [Member] 4.90% Series Due 2025 [Member] First Mortgage Bonds, 4.90% Series Due 2025 [Member] 5.10% Series Due 2025 [Member] First Mortgage Bonds, 5.10% Series Due 2025 [Member] 5.99% Series Due 2027 [Member] First Mortgage Bonds, 5.99% Series Due 2027 [Member] 5.69% Series Due 2036 [Member] First Mortgage Bonds, 5.69% Series Due 2036 [Member] 6.00% Series Due 2040 [Member] First Mortgage Bonds, 6.00% Series Due 2040 [Member] 5.82% Series Due 2040 [Member] First Mortgage Bonds, 5.82% Series Due 2040 [Member] 7.25% Series Due 2013 [Member] SWL&P First Mortgage Bonds, 7.25% Series Due 2013 [Member] Senior Unsecured Notes 5.99% Due 2017 [Member] Senior Unsecured Notes 5.99% Due 2017 Variable Demand Revenue Refunding Bonds Series 1997 A, B, and C Due 2013-2020 [Member] Variable Demand Revenue Refunding Bonds Series 1997 A, B, and C Due 2013-2020 [Member] Industrial Development Revenue Bonds 6.5% Due 2025 [Member] Industrial Development Revenue Bonds 6.5% 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] Unsecured Term Loan Variable Rate Due 2014 [Member] [Domain] Unsecured Variable Rate Term Loan Due 2014 [Member] Unsecured $75 million Variable Rate Term Loan Due 2014 Effectively FIxed w/ Interest Rate Swap[Member] Other Long-Term Debt, 1.0%-8.0% Due 2012-2037 [Member] Other long-term debt instruments not specifically identified elsewhere Debt Instrument [Line Items] Long-term Debt Long-term Debt, Current Maturities Long-term Debt, Excluding Current Maturities Valuation and Qualifying Accounts and Reserves [Text Block] Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] Concentration Risks, Types, No Concentration Percentage [Abstract] Schedule of Customer Information [Table] Schedule of Customer Information [Table] Customer Type [Axis] Customer Type [Axis] Customer Type [Domain] Customer Type [Domain] Large Power Customer [Member] Large Power Customer [Member] Customer Information [Line Items] Customer Information [Line Items] Number of Customers number of customers number of customers (in ones) Accounts Receivable Accounts Receivable, Gross LP Major Customer, Percent of Total Revenue Entity-wide Revenue, Major Customer, Percent of Total Revenue Entity-wide Revenue, Major Customer, Percent of Total Revenue NewPage Bankruptcy Pre-Petition Receivable Bankruptcy Claims, Amount of Claims under Review by Management 2012 Defined Benefit Plan, Expected Future Benefit Payments in Year One 2013 Defined Benefit Plan, Expected Future Benefit Payments in Year Two 2014 Defined Benefit Plan, Expected Future Benefit Payments in Year Three 2015 Defined Benefit Plan, Expected Future Benefit Payments in Year Four 2016 Defined Benefit Plan, Expected Future Benefit Payments in Year Five Years 2017 - 2021 Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter Pension and Other Postretirement Plans, Policy [Policy Text Block] Pension and Other Postretirement Plans, Policy [Policy Text Block] Other Liabilities, Noncurrent [Abstract] Other Other Accrued Liabilities, Noncurrent Total Other Non-Current Liabilities Other Liabilities, Noncurrent Regulated Operations [Abstract] Retail [Member] Retail Customers [Member] Electric [Member] Electric Customer [Member] Natural Gas [Member] Natural Gas Customer [Member] Water [Member] Water Customer [Member] Non-Affiliated Municipal Customers, Municpalities [Member] Non-Affiliated Municipal Customers, Municpalities [Member] Non-Affiliated Municipal Customers, Municpalities [Member] More Likely Than Not Definition MoreLikelyThanNotDefined The percentage guideline to determine more-likely-than-not status Impairement of Long-Lived Assets [Abstract] Long-Lived Asset Impairment [Abstract] Land Impairment Remaining Cost Basis Remaining Cost Basis, Impaired Asset Remaining Cost Basis, Impaired Asset Noncontrolling Interest [Abstract] Purchase of Non-Controlling Interest at Book Value Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests Purchase of Non-Controlling Interest, Shares Issued Stock Issued During Period, Shares, Purchase of Non-Controlling Interest Number of shares of stock issued during the period to purchase non-controlling interest. Prepaid Expense and Other Assets, Current [Abstract] Deferred Fuel Adjustment Clause Deferred Fuel Cost Other Other Assets, Current Total Prepayments and Other Current Assets Prepaid Expense and Other Assets, Current Supplemental Cash Flow Information [Abstract] Cash Paid During the Period for Interest - Net of Amounts Capitalized Interest Paid, Net Cash Received During the Period for Income Taxes Income Taxes Paid, Net Noncash Investing and Financing Activities [Abstract] Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Increase (Decrease) in Accounts Payable for Capital Additions to Property, Plant and Equipment Capital Expenditures Incurred but Not yet Paid AFUDC-Equity Increase (Decrease) in Allowance for Equity Funds Used During Construction ALLETE Common Stock Contributed to the Pension Plan Contribution of Property Accounts Receivable Additional Disclosures [Abstract] Trade Accounts Receivable [Abstract] Trade Accounts Receivable [Abstract] Billed Gross Trade Accounts Receivable, Billed Gross Trade Accounts Receivable, Billed Unbilled Unbilled Receivables, Current Less: Allowance for Doubtful Accounts Allowance for Doubtful Accounts Receivable, Current Total Trade Accounts Receivable Total Trade Accounts Receivable Total Trade Accounts Receivable, Net of allowance for doubtful accounts. Income Taxes Receivable Total Accounts Receivable - Net Accounts Receivable, Net, Current Other Liabilities, Current [Abstract] Customer Deposits Customer Deposits, Current Other Other Accrued Liabilities, Current Total Other Current Liabilities Other Liabilities, Current Inventory Disclosure [Abstract] Fuel Energy Related Inventory, Coal Materials and Supplies Inventory, Raw Materials and Supplies, Net of Reserves Total Inventories Inventory, Net Service Cost Defined Benefit Plan, Service Cost Interest Cost Defined Benefit Plan, Interest Cost Expected Return on Plan Assets Defined Benefit Plan, Expected Return on Plan Assets Amortization of Loss Defined Benefit Plan, Amortization of Gains (Losses) Amortization of Prior Service Costs Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Amortization of Transition Obligation Defined Benefit Plan, Amortization of Transition Obligations (Assets) Net Expense Defined Benefit Plan, Net Periodic Benefit Cost Schedule of Stock by Class [Table] Method of Stock Issuance [Axis] Method of Stock Issuance [Axis] The different ways stock is issued or programs under which stock is issued, for example, an employee stock purchase plan or a stock option program. Method of Stock Issuance [Domain] Method of Stock Issuance [Domain] Method of Stock Issuance [Domain] Equity Issuance Program [Member] Equity Issuance Program [Member] ALLETE's PIE (Periodic Issuance of Equity) Equity Issuance Program [Member] Class of Stock [Axis] Class of Stock [Domain] Common Stock [Member] Class of Stock [Line Items] Common Stock Outstanding, Shares Common Stock, Shares, Outstanding Common Stock Outstanding, Value Common Stock, Value, Outstanding Employee Stock Purchase Program, Shares Stock Issued During Period, Shares, Employee Stock Purchase Plans Employee Stock Purchase Program, Value Stock Issued During Period, Value, Employee Stock Purchase Plan Invest Direct, Shares Stock Issued During Period, Shares, Dividend Reinvestment Plan Invest Direct, Value Stock Issued During Period, Value, Dividend Reinvestment Plan Options and Stock Awards, Shares Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Options and Stock Awards, Value Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Equity Issuance Program, Shares Stock Issued During Period, Shares, Other Equity Issuance Program, Value Stock Issued During Period, Value, Other Purchase of Non-Controlling Interest, Shares Purchase of Non-Controlling Interest, Value Stock Issued During Period, Value, Purchase of Non-Controlling Interest Stock Issued During Period, Value, Purchase of Non-Controlling Interest Contributions to Pension, Shares Contributions to Pension, Value 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). 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). Short-term Debt [Abstract] Short-term Debt Aggregate Lines of Credit, Total Borrowing Capacity Aggregate Lines of Credit, Total Borrowing Capacity Aggregate Lines of Credit, Used Borrowing Capacity Aggregate Lines of Credit, Used Borrowing Capacity Aggregate Lines of Credit, Available Borrowing Capacity Aggregate Lines of Credit, Available Borrowing Capacity (unused/outstanding) Schedule of New Debt [Table] Includes terms and balances of new debt instruments during the period. Credit Agreement Feb 2012 [Member] Credit Agreement Feb 2012 [Member] Credit Agreement w/ JP Morgan Chase Feb 2012 [Member] Credit Agreement July 2011 [Member] Credit Agreement July 2011 [Member] ALLETE Credit Agreement with JPMorgan Chase effective July 1, 2011[Member] Term Loan Agreement [Member] Term Loan Agreement with JPMorgan Chase effective August 25, 2011 [Member] ALLETE Properties LOC Nov 2011 [Member] ALLETE Properties LOC Nov 2011 [Member] ALLETE Properties LOC Nov 2011 [Member] ALLETE Properties LOC Oct 2011 [Member] ALLETE Properties LOC Oct 2011 [Member] ALLETE Properties LOC Oct 2011 [Member] Line of Credit Facility, Maximum Borrowing Capacity Line of Credit Facility, Maximum Borrowing Capacity Line of Credit Borrowing Capacity Reduction Line of Credit Borrowing Capacity Reduction Line of Credit Borrowing Capacity Reduction Letter of Credit Maximum Issuances Letter of Credit Maximum Issuances This represents the allowed amount of letters of credit issuances under another credit agreement. Debt Instrument, Face Amount Debt Instrument, Description of Variable Rate Basis Debt Instrument, Basis Spread on Variable Rate Debt Instrument, Interest Rate, Effective Percentage Debt Instrument, Carrying Amount at Period End The balance sheet gross carrying amount of the specified debt instrument at period end. Financial Covenants [Abstract] Debt Instrument, Required Indebtedness to Total Capital Ratio Indebtedness to total capital ratio required to be maintained by most restrictive financial covenant. Debt Instrument, Actual Indebtedness to Total Capital Ratio Actual indebtedness to total capital ratio required to be maintained by most restrictive financial covenant. Maturities of Long-term Debt [Abstract] Long-term Debt, Maturities, Repayments of Principal in Year Two Long-term Debt, Maturities, Repayments of Principal in Year Three Long-term Debt, Maturities, Repayments of Principal in Year Four Long-term Debt, Maturities, Repayments of Principal in Year Five Long-term Debt, Maturities, Repayments of Principal after Year Five Supplemental Statement of Cash Flow Information [Table Text Block] Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Accounts Receivable [Table Text Block] Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Inventories [Table Text Block] Schedule of Inventory, Current [Table Text Block] Prepayments and Other Current Assets [Table Text Block] Schedule of Other Assets [Table Text Block] Other Liabilities [Table Text Block] Schedule of Other Assets and Other Liabilities [Table Text Block] Commitments, Guarantees and Contingencies [Abstract] Commitments, Guarantees and Contingencies [Abstract] Commitments, Guarantees and Contingencies Commitments and Contingencies Disclosure [Text Block] Jointly Owned Electric Facility [Table] Jointly Owned Utility Plant Interests [Table] Jointly Owned Electric Facility [Axis] Jointly Owned Utility Plant [Axis] Jointly Owned Electric Facility [Domain] Jointly Owned Utility Plant [Domain] Boswell Unit 4 [Member] Boswell Unit 4 [Member] Jointly Owned Electric Facility [Line Items] Jointly Owned Utility Plant Interests [Line Items] Plant in Service Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service Accumulated Depreciation Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation Construction Work in Progress Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress % Ownership Jointly Owned Utility Plant, Proportionate Ownership Share % Ownership Range Jointly Owned Utility Plant, Proportionate Ownership Share Range Jointly Owned Utility Plant, Proportionate Ownership Share Range Coal-fired generating unit capacity Represents MW capacity for coal-fired generating unit near Center, ND. Jointly-Owned Electric Facility Percentage Not Owned Jointly-Owned Electric Facility Percentage Not Owned Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Axis] Plan Asset Categories [Domain] Equity Securities (Auction Rate Securities) [Member] Real Estate [Member] Activity in Level 3 [Line Items] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Actual Return on Plan Assets Defined Benefit Plan, Actual Return on Plan Assets Purchases, Sales and Settlements, Net Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, Sales, Issuances, Settlements ALLETE's Interest in ATC [Table Text Block] Schedule of Equity Method Investments [Table Text Block] ATC Summarized Financial Data [Table Text Block] Equity Method Investment, Schedule of Summarized Financial Data [Table Text Block] Tabular disclosure of summarized financial data reported by an equity method investment of the entity. Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Statement, Equity Components [Axis] Statement, Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Retained Earnings Retained Earnings [Member] Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) [Member] Unearned ESOP Shares Deferred Compensation, Share-based Payments [Member] Common Stock Statement [Line Items] Statement [Line Items] Comprehensive Income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract] Total Shareholders' Equity Stockholders' Equity Attributable to Parent Other Comprehensive Income - Net of Tax Other Comprehensive Income (Loss), Net of Tax [Abstract] Unrealized Gain (Loss) on Securities - Net Unrealized Loss on Derivatives - Net Defined Benefit Pension and Other Postretirement Plans Non-Controlling Interest in Subsidiaries Common Stock Issued - Net Stock Issued During Period, Value, New Issues Dividends Declared Dividends, Common Stock ESOP Shares Earned Stock Issued During Period, Value, Employee Stock Ownership Plan Total Shareholders' Equity Quarterly Financial Data (Unaudited) [Abstract] Quarterly Financial Data (Unaudited) [Abstract] Quarterly Financial Data (Unaudited) [Table Text Block] Schedule of Quarterly Financial Information [Table Text Block] Derivatives [Abstract] DERIVATIVES [Abstract] Derivatives [Text Block] Derivative Instruments and Hedging Activities Disclosure [Text Block] Operating Revenue Operating Income Gross Unrecognized Income Tax Benefits [Abstract] Gross Unrecognized Income Tax Benefits [Abstract] Unrecognized Tax Benefits that Would Impact Effective Tax Rate Accrued Interest Unrecognized Tax Benefits, Interest on Income Taxes Accrued Interest Expense Unrecognized Tax Benefits, Interest on Income Taxes Expense Penalties Unrecognized Tax Benefits, Income Tax Penalties Expense Reasonably Possible Change in Unrecognized Tax Benefits in Next 12 Months Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Balance at January 1 Unrecognized Tax Benefits Additions for Tax Positions Related to the Current Year Unrecognized Tax Benefits, Increases Resulting from Current Period Tax Positions Reductions for Tax Positions Related to the Current Year Unrecognized Tax Benefits, Decreases Resulting from Current Period Tax Positions Additions for Tax Positions Related to Prior Years Unrecognized Tax Benefits, Increases Resulting from Prior Period Tax Positions Reduction for Tax Positions Related to Prior Years Unrecognized Tax Benefits, Decreases Resulting from Prior Period Tax Positions Settlements Unrecognized Tax Benefits, Decreases Resulting from Settlements with Taxing Authorities Lapse of Statute Unrecognized Tax Benefits, Reductions Resulting from Lapse of Applicable Statute of Limitations Balance as of December 31 Stock Options, Range of Exercise Price [Table] Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table] Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Axis] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Domain] $18.85 to $29.79 [Member] $18.85 to $29.79 Exercise Price Range, Stock Options[Member] $37.76 to $41.35 [Member] $37.76 to $41.35 Exercise Price Range, Stock Options [Member] $44.15 to $48.65 [Member] $44.15 to $48.65 Exercise Price Range, Stock Options [Member] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] Number Outstanding and Exercisable Weighted Average Remaining Contracutal Life (Years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Weighted Average Exercise Price Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price Property, Plant, and Equipment [Table Text Block] Schedule of Public Utility Property, Plant, and Equipment [Table Text Block] Estimated Useful Lives of Property, Plant and Equipment [Table Text Block] Property, Plant and Equipment [Table Text Block] Asset Retirement Obligation [Table Text Block] Schedule of Change in Asset Retirement Obligation [Table Text Block] Net Loss Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax Prior Service Cost (Credit) Arising During Period Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Prior Service Cost (Credit) Arising During Period, before Tax Amortization of Prior Service Cost Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost (Credit) Recognized in Net Periodic Benefit Cost, before Tax Amortization of Transition Obligation Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Transition Asset (Obligation), Recognized in Net Periodic Benefit Cost, before Tax Amortization of Gain (Loss) Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax Total Recognized in Other Comprehensive Income and Regulatory Assets Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax Number of acres of land available-for-sale (in acres) Number of acres of land available-for-sale (in acres) Number of acres of land available-for-sale. Business Segments [Table] Schedule of Segment Reporting Information, by Segment [Table] Business Segments [Axis] Statement, Business Segments [Axis] Segment [Domain] Segment [Domain] Consolidated [Member] Consolidated Entities [Member] Regulated Operations [Member] Investments and Other [Member] Investment and Other [Member] Business Segments [Line Items] Segment Reporting Information [Line Items] Operating Revenue Operating Revenue, Excluding Prior Year Rate Refunds Operating Revenue, Excluding Prior Year Rate Refunds Prior Year Rate Refunds Prior Year Rate Refunds Prior Year Rate Refunds Included in Operating Revenues Operating Revenue Segment Reporting Information, Revenue for Reportable Segment Total Operating Revenue Fuel and Purchased Power Expense Operating and Maintenance Expense Interest Expense Other Income (Expense) Income (Loss) Before Non-Controlling Interest and Income Taxes Income Tax Expense (Benefit) Net Income (Loss) Net Income (Loss) Attributable to ALLETE Total Assets Assets Capital Additions Property, Plant and Equipment, Additions Statement of Financial Position [Abstract] Assets Assets [Abstract] Current Assets Assets, Current [Abstract] Cash and Cash Equivalents Short-Term Investments Short-term Investments Accounts Receivable (Less Allowance of $0.9 and $0.9) Inventories Prepayments and Other Prepaid Expense, Current Total Current Assets Assets, Current Property, Plant and Equipment - Net Regulatory Assets Investment in ATC Other Investments Other Non-Current Assets Other Assets, Noncurrent Total Assets Liabilities and Equity Liabilities and Equity [Abstract] Liabilities Liabilities [Abstract] Current Liabilities Liabilities, Current [Abstract] Accounts Payable Accounts Payable, Current Accrued Taxes Taxes Payable, Current Accrued Interest Interest Payable, Current Long-Term Debt Due Within One Year Notes Payable Notes Payable, Current Other Total Current Liabilities Liabilities, Current Long-Term Debt Deferred Income Taxes Deferred Tax Liabilities, Noncurrent Regulatory Liabilities Defined Benefit Pension and Other Postretirement Benefit Plans Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent Other Non-Current Liabilities Total Liabilities Liabilities Commitments and Contingencies (Note 11) Commitments and Contingencies Equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] ALLETE's Equity Stockholders' Equity Attributable to Parent [Abstract] Common Stock Without Par Value, 80.0 Shares Authorized, 37.5 and 35.8 Shares Outstanding Common Stock, Value, Issued Unearned ESOP Shares Unearned ESOP Shares Accumulated Other Comprehensive Loss Retained Earnings Retained Earnings (Accumulated Deficit) Total ALLETE Equity Non-Controlling Interest in Subsidiaries Stockholders' Equity Attributable to Noncontrolling Interest Total Equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Total Liabilities and Equity Liabilities and Equity Principles of Consolidation [Policy Text Block] Consolidation, Policy [Policy Text Block] Cash and Cash Equivalents [Policy Text Block] Cash and Cash Equivalents, Policy [Policy Text Block] Accounts Receivable [Policy Text Block] Trade and Other Accounts Receivable, Policy [Policy Text Block] Long-Term Finance Receivables [Policy Text Block] Finance, Loans and Leases Receivable, Policy [Policy Text Block] Available-for-sale Securities [Policy Text Block] Marketable Securities, Available-for-sale Securities, Policy [Policy Text Block] Inventories [Policy Text Block] Inventory, Policy [Policy Text Block] Property, Plant and Equipment [Policy Text Block] Property, Plant and Equipment, Policy [Policy Text Block] Long-Lived Asset Impairments [Policy Text Block] Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Derivatives [Policy Text Block] Derivatives, Policy [Policy Text Block] Accounting for Stock-Based Compensation [Policy Text Block] Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Environmental Liabilities [Policy Text Block] Environmental Costs, Policy [Policy Text Block] Revenue Recognition [Policy Text Block] Revenue Recognition, Policy [Policy Text Block] Unamortized Discount and Premium on Debt [Policy Text Block] Unamortized Discount and Premium on Debt Policy [Policy Text Block] Method of amortization used for unamortized discounts and premiums related to debt instruments. Income Taxes [Policy Text Block] Income Tax, Policy [Policy Text Block] Excise Taxes [Policy Text Block] Excise Tax Policy [Policy Text Block] Policy regarding the collection and recording of excise taxes. AFUDC - Equity Investment and Other Income (Expense) Other Income Total Other Income Depreciation [Policy Text Block] Asset Retirement Obligations [Policy Text Block] Asset Retirement Obligations, Policy [Policy Text Block] Environmental Matters [Abstract] Environmental Matters [Abstract] Environmental Matters [Table] Schedule of Environmental Exit Cost [Table] Environmental Matters [Axis] Environmental Exit Cost by Property [Axis] Environmental Matters [Domain] Environmental Exit Costs, Name of Property [Domain] Boswell Unit 4 [Member] Manufactured Gas Plant Site [Member] Manufactured Gas Plant Site [Member] Manufactured gas plant site that requires remediation as a result of unanticipated contamination of the assets. Environmental Matters [Line Items] Environmental Exit Cost [Line Items] minimum amount expected to be invested for compliance costs minimum amount expected to be invested for compliance costs The minimum amount expected to be invested for compliance costs of the MATS Rule. maximum amount expected to be invested for compliance costs maximum amount expected to be invested for compliance costs The maximum amount expected to be invested for compliance costs for the MATS Rule. Liability for Remediation of Manufactured Gas Plant Site Environmental Exit Costs, Assets Previously Disposed, Liability for Remediation Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangement by Share-based Payment Award, Award Type and Plan Name [Axis] Share-based Compensation Arrangements by Share-based Payment Award, Award Type and Plan Name [Domain] Long-Term Incentive Compensation, Director Plan [Member] Long-Term Incentive Compensation, Director Plan [Member] Long-Term Incentive Compensation, Director Plan [Member] Long-Term Incentive Compensation, Executive Plan [Member] Long-Term Incentive Compensation, Executive Plan [Member] Long-Term Incentive Compensation, Executive Plan [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Common Stock Reserved Common Stock, Capital Shares Reserved for Future Issuance Shares Available for Issuance Grants under Director Plan Options Outstanding PSA Performance Period Performance Period Performance Period Length (usually in years) RSU Vesting Period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period ESPP Discount Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date Stock Options [Member] Stock Options [Member] Performance Shares Awards [Member] Performance Shares Awards [Member] Performance Shares Awards [Member] Restricted Stock Units (RSUs) [Member] Income Tax Benefit Employee Service Share-based Compensation, Tax Benefit from Compensation Expense Capitalized Stock-Based Compensation Expense Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount Unrecognized Compensation Cost Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized Weighted Average Period for Recognition Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition Land Held-for-Sale [Policy Text Block] Real Estate Held for Development and Sale, Policy [Policy Text Block] Regulatory Matters [Text Block] Public Utilities Disclosure [Text Block] Pension and Other Postretirement Benefit Plans Recurring Fair Value Measures [Table] U.S. Large-Cap [Member] Equity Securities, U.S. Large-Cap [Member] U.S. Mid-Cap Growth [Member] Equity Securities, U.S. Mid-Cap Growth [Member] U.S. Small Cap [Member] Equity Securities, U.S. Small Cap [Member] International [Member] Equity Securities, International [Member] Allete [Member] Allete [Member] Mutual Funds [Member] Debt Securities, Mutual Funds [Member] Fixed Income Funds [Member] Defined Benefit Plan, Fair Value of Plan Assets by Measurement [Axis] Defined Benefit Plan, Fair Value of Plan Assets by Measurement [Axis] Fair Value Plan Asset Measurement [Domain] Fair Value Plan Asset Measurement [Domain] Level 1 [Member] Level 2 [Member] Level 3 [Member] Recurring Fair Value Measures [Line Items] Fair Value of Plan Assets Defined Benefit Plan, Fair Value of Plan Assets Non-vested Performance Shares [Rollforward] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward] Non-vested as of January 1, Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Awarded Performance Shares Awarded Performance Shares Awarded for a specified performance period 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, Unearned Grant Award Non-vested as of December 31, 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 (Per Share) 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) Performance Share Grants, Grant Date Fair Value Performance Share Grants, Grant Date Fair Value, Total Performance Share Grants, Grant Date Fair Value, Total Performance Share Awards, Grant Date Fair Value Performance Share Awards Grant Date Fair Value, Total Performance Share Awards Grant Date Fair Value, Total Performance Period Employee Stock and Incentive Plans [Text Block] Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Deferred Tax Assets [Abstract] Deferred Tax Assets, Gross [Abstract] Employee Benefits and Compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation Property Related Deferred Tax Asset, Property Related Deferred Tax Asset, Property Related NOL and Tax Credit Carryforward NOL and Tax Credit Carryforwards, Deferred Tax Asset NOL and Tax Credit Carryforwards, Deferred Tax Asset Investment Tax Credits Deferred Tax Assets, Tax Credit Carryforwards, Other Other Deferred Tax Assets, Other Gross Deferred Tax Assets Deferred Tax Assets, Gross Deferred Tax Asset Valuation Allowance Deferred Tax Assets, Valuation Allowance Total Deferred Tax Assets Deferred Tax Assets, Net Deferred Tax Liabilities [Abstract] Property Related Deferred Tax Liabilities, Property, Plant and Equipment Regulatory Asset for Benefit Obligations Deferred Tax Liabilities, Regulatory Assets Unamortized Investment Tax Credits Deferred Tax Liability, Unamortized Investment Tax Credits Deferred Tax Liability, Unamortized Investment Tax Credits Partnership Basis Differences Deferred Tax Liabilty, Partnership Basis Differences Deferred Tax Liabilty, Partnership Basis Differences Other Deferred Tax Liabilities, Other Total Deferred Tax Liabilities Deferred Tax Liabilities Net Deferred Income Taxes Deferred Tax Assets (Liabilities), Net Net Current Deferred Tax Liabilities Deferred Tax Liabilities, Current Net Long-Term Deferred Tax Liabilities Accumulated Benefit Obligation Defined Benefit Plan, Accumulated Benefit Obligation Change in Benefit Obligation [Roll Forward] Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Obligation, Beginning of Year Defined Benefit Plan, Benefit Obligation Actuarial Loss (Gain) Defined Benefit Plan, Actuarial Net (Gains) Losses Benefits Paid Defined Benefit Plan, Benefits Paid Participant Contributions Defined Benefit Plan, Contributions by Plan Participants Plan Amendments Defined Benefit Plan, Plan Amendments Obligation, End of Year Change in Plan Assets [Roll Forward] Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Fair Value, Beginning of Year Employer Contribution Defined Benefit Plan, Contributions by Employer Participant Contributions Defined Benefit Plan Contributions by Plan Participants, Excluding Key Employees Defined Benefit Plan Contributions by Plan Participants, Excluding Key Employees Benefits Paid Defined Benefit Plan, Benefits Paid, Excluding Key Employees Defined Benefit Plan, Benefits Paid, Excluding Key Employees Fair Value, End of Year Funded Status, End of Year Defined Benefit Plan, Funded Status of Plan Current Liabilities Pension and Other Postretirement Defined Benefit Plans, Current Liabilities Non-Current Liabilities Other Investments Comprehensive Income (Loss) [Text Block] Comprehensive Income (Loss) Note [Text Block] Interest Rate Swap [Abstract] Interest Rate Cash Flow Hedges [Abstract] Term Loan, Face Amount Term Loan, Description of Variable Rate Basis Term Loan, Basis Spread on Variable Rate Percentage of Debt Hedged by Interest Rate Derivatives Percentage of Debt Hedged by Interest Rate Derivatives Derivative, Fixed Interest Rate Derivative, Fixed Interest Rate Discussion of Interest Rate Cash Flow Hedge Effectiveness Assessment and Measurement Discussion of Interest Rate Cash Flow Hedge Effectiveness Assessment and Measurement Interest Rate Cash Flow Hedge Liability at Fair Value Jointly-Owned Electric Facility [Text Block] Jointly-Owned Electric Facility [Text Block] Jointly-Owned Electric Facility [Text Block] Quarterly Financial Data (Unaudited) [Text Block] Quarterly Financial Information [Text Block] Income Tax Expense [Text Block] Income Tax Disclosure [Text Block] Business Segments [Table Text Block] Schedule of Segment Reporting Information, by Segment [Table Text Block] Pension and Other Postretirement Benefit Plans [Text Block] Pension and Other Postretirement Benefits Disclosure [Text Block] NOL and Tax Credit Carryforwards [Table] NOL and Tax Credit Carryforwards [Table] NOL and Tax Credit Carryforwards [Table] Income Tax Authority [Axis] Income Tax Authority [Domain] Federal [Member] Internal Revenue Service (IRS) [Member] State [Member] State and Local Jurisdiction [Member] NOL and Tax Credit Carryforwards [Line Items] NOL and Tax Credit Carryforwards [Line Items] NOL Carryforward Operating Loss Carryforwards Tax Credit Carryforwards Tax Credit Carryforward, Amount Charitable Contributions Carryforward Other Tax Carryforward, Gross Amount Weighted-Average Assumptions Used to Determine Benefit Obligation [Abstract] Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract] Discount Rate Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate Rate of Compensation Increase Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase (Range) Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase (Percentage Range) Text Item Type Trend Rate Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year Ultimate Trend Rate Defined Benefit Plan, Ultimate Health Care Cost Trend Rate Year Ultimate Trend Rate Effective Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate Weighted-Average Assumptions Used to Determine Net Periodic Benefit Costs [Abstract] Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract] Discount Rate (Range) Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Expense, Discount Rate (Range) Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Expense, Discount Rate (Range) Discount Rate Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Expected Long-Term Return on Plan Assets Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets (Range) Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets (Percentage Range) Text item type Rate of Compensation Increase Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase (Range) Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase (Percentage Range) Text item type Revised Expected Long-term Rate of Return Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets Investments [Text Block] Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Document Information [Text Block] Document Information [Table] Document Information [Table] Document Information, Document [Axis] Document Information, Document [Axis] Document [Domain] Document [Domain] Document Information [Line Items] Document Information [Line Items] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers Entity Current Reporting Status Entity Current Reporting Status Entity Filer Category Entity Filer Category Entity Public Float Entity Public Float Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Consolidated Balance Sheet Parenthetical [Abstract] 25ac8a1e-d965-11e0-8c71-12313b06a4a2 Accounts Receivable, Allowance Accounts Receivable, Allowance Common Stock Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract] Common Stock, Par Value Common Stock, Par or Stated Value Per Share Common Stock, Shares Authorized Common Stock, Shares Authorized Common Stock, Shares Outstanding