Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Trading Arrangement: Trading Arrangement [Axis] Maximum Maximum [Member] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Statistical Measurement [Domain] Statistical Measurement [Domain] Less Accumulated Depreciation Public Utilities, Property, Plant and Equipment, Accumulated Depreciation Title of 12(b) Security Title of 12(b) Security Carrying Amount Reported Value Measurement [Member] Subsequent Event Subsequent Event [Member] Debt Securities, Available-for-Sale [Table] Debt Securities, Available-for-Sale [Table] Document Fiscal Year Focus Document Fiscal Year Focus Debt, weighted average interest rate (as a percent) Debt, Weighted Average Interest Rate Adjustment to Compensation, Amount Adjustment to Compensation Amount Series 2026A Senior Unsecured Notes Senior Unsecured Notes 5.33%, Series A, Due March 19, 2036 [Member] Senior Unsecured Notes 5.33%, Series A, Due March 19, 2036 Financial Instrument [Axis] Financial Instrument [Axis] Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Series 2021B Senior Unsecured Notes Senior Unsecured Notes 3.69%, Series B, Due November 29, 2051 [Member] Senior Unsecured Notes 3.69%, Series B, Due November 29, 2051 Segment Reporting [Abstract] Common Shares: 50,000,000 shares authorized, $5 par value; 41,985,580 and 41,905,520 outstanding at June 30, 2026 and December 31, 2025 Common Stock, Value, Issued Payments for Shares Withheld for Employee Tax Obligations Payment, Tax Withholding, Share-Based Payment Arrangement Accrued Salaries and Wages Employee-related Liabilities, Current Employee Postretirement Benefits Retirement Benefits [Text Block] Restatement Determination Date Restatement Determination Date Expected Return on Assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Series 2018A Senior Unsecured Notes Senior Unsecured Notes 4.07%, Series A, Due February 7, 2048 [Member] Represents information about Senior Unsecured Notes 4.07%, Series 2018A, due February 7, 2048. Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Instruments Regulatory Asset- Derivative Instruments [Member] Regulatory Asset- Derivative Instruments Less: Allowance for Credit Losses Beginning Balance, January 1 Ending Balance, June 30 Accounts Receivable, Allowance for Credit Loss Retail: Commercial and Industrial Retail, Commercial and Industrial [Member] Retail, Commercial and Industrial Pension and Other Postretirement Benefits Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits Long-term Investments Long-Term Investments [Abstract] Regulatory Liabilities Regulatory liabilities, long -term Regulatory Liability, Noncurrent Proceeds from Disposal of Noncurrent Assets Proceeds from Sale of Productive Assets Series 2021A Senior Unsecured Notes Senior Unsecured Notes 2.74%, Series A, Due November 29, 2031 [Member] Senior Unsecured Notes 2.74%, Series A, Due November 29, 2031 Amendment Flag Amendment Flag Current Liabilities Liabilities, Current [Abstract] Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Stock Purchase Plan Expenses Stock Issued During Period, Value, Dividend Reinvestment and Employee Stock Purchase Plans Stock Issued During Period, Value, Dividend Reinvestment and Employee Stock Purchase Plans Product Sales Product Sales [Member] Product Sales Gross Unrealized (Losses) Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax Schedule of Amortized Costs and Fair Value of Debt Securities, Available-for-Sale Debt Securities, Available-for-Sale [Table Text Block] Guaranteed Senior Notes The 3.55% Guaranteed Senior Notes, Due December 15, 2026 [Member] Represents information about 3.55% Guaranteed Senior Notes, due December 15, 2026. Series 2025B Senior Unsecured Notes Senior Unsecured Notes 5.98%, Series B, Due June 05, 2055 [Member] Senior Unsecured Notes 5.98%, Series B, Due June 05, 2055 Total Noncurrent Liabilities Liabilities, Noncurrent Regulatory assets - Remaining Recovery/Refund Period Regulatory Asset, Amortization Period Scrap Metal Scrap Metal [Member] Scrap Metal Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Settlements Asset Retirement Obligation, Liabilities Settled Schedule of Restricted and Unrestricted Cash Schedule of Cash and Cash Equivalents [Table Text Block] Nonelectric Property, Plant and Equipment Property, Plant, and Equipment [Abstract] Entity Address, State or Province Entity Address, State or Province PEO Total Compensation Amount PEO Total Compensation Amount Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Assets: Assets, Fair Value Disclosure [Abstract] Capital Expenditures Segment Reporting, Long-Lived Asset, Expenditure for Addition Noncurrent Liabilities Liabilities, Noncurrent [Abstract] Intangible Assets, net of accumulated amortization Intangible Asset, Excluding Goodwill, after Accumulated Amortization Beginning of year (in shares) End of year (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Accrued and Other Liabilities Increase (Decrease) in Accrued Liabilities and Other Operating Liabilities Basic (in shares) Weighted-Average Common Shares Outstanding – Basic (in shares) Weighted Average Number of Shares Outstanding, Basic Total Retail Electronic Product, Retail [Member] Electronic Product, Retail Retirement Benefits [Abstract] Investments Total Long-term Investments Long-Term Investments Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Total Capitalization Total capitalization Capitalization, Long-Term Debt and Equity Beginning Balance, January 1 Ending Balance, June 30 Asset Retirement Obligation Regulatory Assets Regulatory assets, long-term Regulatory Asset, Noncurrent Series 2022A Senior Unsecured Notes Senior Unsecured Notes 3.77%, Series A, Due May 20, 2052 [Member] Senior Unsecured Notes 3.77%, Series A, Due May 20, 2052 Number of reportable segments Number of Reportable Segments Income (Loss) Before Income Taxes Income (Loss) Attributable to Parent, before Tax Total Current Liabilities Liabilities, Current Regulatory Liability [Axis] Regulatory Liability [Axis] Work in Process Inventory, Work in Process, Net of Reserves Other Current Liabilities Derivative Liability, Current Due in five to ten years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Schedule of Notional Amounts and Fair Value of Derivative Instruments Schedule of Derivative Instruments [Table Text Block] Manufacturing Manufacturing [Member] Represents information about manufacturing. Entity Address, City or Town Entity Address, City or Town Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Interest and dividend coverage ratio Interest And Dividend Coverage Ratio Represents the required interest and dividend coverage ratio. Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Vested (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Total Receivables Accounts Receivable, before Allowance for Credit Loss Level 2 Fair Value, Inputs, Level 2 [Member] Other Income and (Expense) Nonoperating Income (Expense) [Abstract] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Net Periodic Benefit Cost (Income) Recognized Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Net of Deferrals Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Net of Deferrals Borrowing Limit Line of Credit Facility, Maximum Borrowing Capacity Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Current Maturities of Long-Term Debt Current Maturities, Net of Unamortized Debt Issuance Costs Long-Term Debt, Current Maturities Subsequent Event Type [Axis] Subsequent Event Type [Axis] Number of putative classes Number Of Putative Classes Number Of Putative Classes Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Regulatory liabilities - Remaining Recovery/Refund Period Regulatory Liability, Amortization Period Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Litigation Case [Axis] Litigation Case [Axis] Accrued Property, Plant and Equipment Additions Capital Expenditures Incurred but Not yet Paid Land Land [Member] Schedule of Segment Reporting Information, by Segment Segment Reporting [Table Text Block] Use of Estimates Use of Estimates, Policy [Policy Text Block] Total Other Comprehensive Income (Loss) Other Comprehensive Income (Loss) Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Estimated loss Estimated Litigation Liability, Current Long-Term Debt Total Long-Term Debt, Net of Unamortized Debt Issuance Costs Long-Term Debt Due in one to five years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five Document Period End Date Document Period End Date Changes in Operating Assets and Liabilities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Net Cash Used in Investing Activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Series 2019C Senior Unsecured Notes Senior Unsecured Notes 3.82%, Series C, Due October 10, 2049 [Member] Related to debt. Shareholders' Equity Equity [Text Block] Operating Expenses Costs and Expenses [Abstract] Security Exchange Name Security Exchange Name Unrealized Gain on Available-for-Sale Securities, tax expense OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax Series 2024B Senior Unsecured Notes Senior Unsecured Notes 5.77%, Series B, Due April 01, 2054 [Member] Senior Unsecured Notes 5.77%, Series A, Due April 01, 2054 Other Electric Product, Other [Member] Electric Product, Other Total Liabilities Liabilities, Fair Value Disclosure Fair value of awards vested Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Accumulated Other Comprehensive Income Accumulated Other Comprehensive Income (Loss), Net of Tax Entity Shell Company Entity Shell Company Consolidation Items [Domain] Consolidation Items [Domain] Pension contribution Payment for Pension Benefits Schedule of Activity in Allowance for Credit Losses Accounts Receivable, Allowance for Credit Loss [Table Text Block] Schedule of Property, Plant and Equipment Property, Plant, and Equipment [Table Text Block] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Earnings Per Share Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Earnings Per Share [Abstract] Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Document Fiscal Period Focus Document Fiscal Period Focus Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Net assets restricted from distribution Net Assets Restricted From Distribution Represents net assets restricted from distribution. Pension and Other Postretirement Benefits, net of tax benefit (expense) Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax, Attributable to Parent Trading Symbol Trading Symbol Revenue, interim rate increase, amount Public Utilities, Interim Rate Increase (Decrease), Amount Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Electric Purchased Power Utilities Operating Expense, Purchased Power Approved rate increase, amount Public Utilities, Approved Rate Increase (Decrease), Amount Retail: Other Retail, Other [Member] Retail, Other Company Selected Measure Name Company Selected Measure Name Sale of Stock [Domain] Sale of Stock [Domain] MPUC MPUC [Member] MPUC Legal Settlement Expenses Legal Settlement Expenses Gain (Loss) from Litigation Settlement Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Schedule of Restricted and Unrestricted Cash Restrictions on Cash and Cash Equivalents [Table Text Block] Income Tax Disclosure [Abstract] Effect of Dilutive Securities: Weighted Average Number of Shares Outstanding, Diluted, Adjustment [Abstract] Unrealized Gains (Losses) on Available-for-Sale Securities, net of tax (expense) benefit of $43, $0, $108 and ($66) OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax Other Investments Other Long-Term Investments Supplemental Disclosure of Noncash Investing Activities Noncash Investing and Financing Items [Abstract] Pension and Other Postretirement Benefits Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Series 2019A Senior Unsecured Notes Senior Unsecured Notes 3.07%, Series A, Due October 10, 2029 [Member] Represents series A senior unsecured notes 3.07% due October 10, 2019. Long-term debt Long-Term Debt, Gross Operating Activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Compensation Amount Outstanding Recovery Compensation Amount Individual: Individual [Axis] Net Amount Amortized Due to the Effect of Regulation Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Deferred Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Deferred Diluted (in shares) Weighted-Average Common Shares Outstanding – Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Entity Emerging Growth Company Entity Emerging Growth Company Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] Line of Credit Facility [Table] Line of Credit Facility [Table] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Derivative Instruments Derivative Instruments and Hedging Activities Disclosure [Text Block] South Dakota Rate Case South Dakota Rate Case [Member] South Dakota Rate Case Investments: Investments, Fair Value Disclosure [Abstract] Regulatory Asset [Axis] Regulatory Asset [Axis] Money Market Funds Cash Equivalent, Money Market Fund, Carrying Value Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Short-Term Debt Amount Outstanding Short-Term Debt Series 2013B Senior Unsecured Notes Senior Unsecured Notes 5.47%, Series B, Due February 27, 2044 [Member] Represents information about Senior Unsecured Notes 5.47%, Series B, due February 27, 2044. Revenue from Contract with Customer [Abstract] Dilutive Effect of Potential Common Shares (in shares) Weighted Average Number of Shares Outstanding, Diluted, Adjustment Common stock shares issued not disclosed Common Stock, Shares, Issued Not Disclosed Common Stock, Shares, Issued Not Disclosed Award Timing Predetermined Award Timing Predetermined [Flag] Restricted Cash Restricted cash Restricted Cash, Current Letters of credit outstanding, amount Letters of Credit Outstanding, Amount Net Electric Plant Public Utilities, Property, Plant and Equipment, Net Debt Securities, Available-for-Sale [Line Items] Debt Securities, Available-for-Sale [Line Items] Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Stock Compensation Expense APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Level 1 Fair Value, Inputs, Level 1 [Member] Other Noncurrent Assets Derivative Asset, Noncurrent Effective income tax rate (as a percent) Effective Income Tax Rate Reconciliation, Percent Organization, Consolidation and Presentation of Financial Statements [Abstract] Lease to be paid Lessee, Operating Lease, Liability, to be Paid Effect of Dilutive Securities (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements Beginning of year (in dollars per share) End of year (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value All Executive Categories All Executive Categories [Member] Swap Swap [Member] Government Debt Securities US Government Debt Securities [Member] Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Other Comprehensive Income (Loss): Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Long-Term Debt Long-Term Debt, Fair Value Percentage of target amount as actual payment (as a percent) Percentage Of Target Amount As Actual Payment Represents the percentage of target amount as a actual payment. Schedule of Net Periodic Benefit Cost (Income) Schedule of Net Benefit Costs [Table Text Block] Option to extend, term Lessee, Operating Lease, Renewal Term Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Fair Value Disclosures [Abstract] Approved rate increase, percent (as a percent) Public Utilities, Approved Rate Increase (Decrease), Percentage Debt Disclosure [Abstract] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Segment Information Segment Reporting [Text Block] Minimum Minimum [Member] Expiration Date Trading Arrangement Expiration Date Schedule of Regulatory Assets and Liabilities [Line Items] Schedule of Regulatory Assets and Liabilities [Line Items] Schedule of Regulatory Assets and Liabilities Series 2007D Senior Unsecured Notes Senior Unsecured Notes 6.47%, Series D, Due August 20, 2037 [Member] Represents information about Senior Unsecured Notes 6.47%, Series D, due August 20, 2037. Schedule of Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Weighted-Average Common Shares Outstanding: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Purchases of Investments and Other Assets Payments for (Proceeds from) Investments Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Money Market Funds Cash and Cash Equivalents Cash and Cash Equivalents, Fair Value Disclosure Series 2007C Senior Unsecured Notes Senior Unsecured Notes 6.37%, Series C, Due August 02, 2027 [Member] Represents information about Senior Unsecured Notes 6.37%, Series C, due August 02, 2027. Public Utilities, Regulatory Proceeding [Domain] Public Utilities, Regulatory Proceeding [Domain] Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Unbilled Receivables Unbilled Receivables, Current Requested rate increase, amount Public Utilities, Requested Rate Increase (Decrease), Amount Net Periodic Benefit Cost (Income) Net Periodic Benefit Cost (Income) Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Deferred Tax Credits Accumulated Deferred Investment Tax Credit Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Common stock, shares authorized (in shares) Common Stock, Shares Authorized NCSP Settlement Agreement NCSP Settlement Agreement [Member] NCSP Settlement Agreement Earnings (Loss) Per Share: Earnings Per Share Reconciliation [Abstract] Deferred Tax Credits Income Tax Credits and Adjustments Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Number of shares issued (in shares) Sale of Stock, Number of Shares Issued in Transaction Asset Retirement Obligation Disclosure [Abstract] Exercise Price Award Exercise Price Investing Activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Segment Reporting [Line Items] Segment Reporting [Line Items] Requested return on base rate, percent (as a percent) Public Utilities, Requested Return On Rate Base, Percentage Public Utilities, Requested Return On Rate Base, Percentage Document Quarterly Report Document Quarterly Report Derivative Assets: Derivative Asset [Abstract] Receivables Accounts, Notes, Loans and Financing Receivable, Unclassified [Abstract] Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Segments [Domain] Segments [Domain] Regulatory Liabilities Increase (Decrease) in Regulatory Liabilities Receivables, net of allowance for credit losses Receivables, net of allowance for credit losses Accounts Receivable, after Allowance for Credit Loss Short-Term and Long-Term Borrowings Debt Disclosure [Text Block] Regulatory Assets and Liabilities Disclosure [Abstract] Regulatory Assets and Liabilities Disclosure [Abstract] Derivative Liabilities: Derivative Liability [Abstract] Series 2020A Senior Unsecured Notes Senior Unsecured Notes 3.22%, Series A, Due February 25, 2030 [Member] Senior Unsecured Notes 3.22%, Series A, Due February 25, 2030 Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Equity Component [Domain] Equity Component [Domain] PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Reductions for Amounts Written Off, Net of Recoveries Accounts Receivable, Allowance for Credit Loss, Writeoff, after Recovery Accounts Receivable, Allowance for Credit Loss, Writeoff, after Recovery Retail: Residential Retail, Residential [Member] Retail, Residential Trade Accounts Receivable, before Allowance for Credit Loss, Current Total Operating Expenses Costs and Expenses Adoption Date Trading Arrangement Adoption Date Interest rate (as a percent) Rate Debt Instrument, Interest Rate, Stated Percentage Common Dividends Dividends, Common Stock, Cash Total Shareholders' Equity Balance, Beginning of Period Balance, End of Period Equity, Attributable to Parent Short-term Investments Short-Term Investments [Abstract] Minnesota Public Utilities Commission Minnesota Public Utilities Commission [Member] Represents information about Minnesota Public Utilities Commission. Revenue, interim rate increase, percentage (as a percent) Public Utilities, Interim Rate Increase (Decrease), Percentage Assets Assets [Abstract] Regulatory Agency [Axis] Regulatory Agency [Axis] Title Trading Arrangement, Individual Title Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost Accounting Policies [Abstract] Accounting Policies [Abstract] Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Risk-free interest rate Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Requested return on equity, percent (as a percent) Public Utilities, Requested Return on Equity, Percentage Requested accelerated recovery of remaining investments Public Utilities, Requested Accelerated Recovery Of Remaining Investments Public Utilities, Requested Accelerated Recovery Of Remaining Investments Insider Trading Policies and Procedures [Line Items] Regulatory Agency [Domain] Regulatory Agency [Domain] Other, net Proceeds from (Payment for) Other Financing Activity Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Stock Performance Awards Performance Cash Settled Awards Performance Shares [Member] Derivative Instruments Derivative Instruments and Hedges, Liabilities Schedule of Line of Credit Facilities Schedule of Line of Credit Facilities [Table Text Block] Deferred Income Taxes Deferred Income Tax Expense (Benefit) Nonelectric Selling, General, and Administrative Expenses Selling, General, and Administrative Expenses Selling, General and Administrative Expense Select Balance Sheet Information Supplemental Balance Sheet Disclosures [Text Block] Regulatory Assets Regulatory assets - current Regulatory Asset, Current Transmission Electric Transmission [Member] Other Other Regulatory Assets [Member] Other Regulatory Assets Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Units excluded from computation (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Entity Central Index Key Entity Central Index Key Less Accumulated Depreciation Property, Plant, and Equipment, Accumulated Depreciation, Depletion, and Amortization Additional Paid-In Capital Additional Paid in Capital, Common Stock All Adjustments to Compensation All Adjustments to Compensation [Member] Corporate Segment Reporting, Reconciling Item, Corporate Nonsegment [Member] Equity [Abstract] Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Net Cash Provided by Operating Activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Performance Cash Settled Awards Performance Cash Settled Awards [Member] Performance Cash Settled Awards Electric Property Taxes Property Taxes Utilities Operating Expense, Property Taxes Utilities Operating Expense, Property Taxes Income Statement [Abstract] Income Statement [Abstract] Shareholders' Equity Equity, Attributable to Parent [Abstract] Document Transition Report Document Transition Report Plastics Plastics [Member] Represents information about plastics or the Plastics segment. Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Investment Losses Gain (Loss) on Investments Metal Parts and Tooling Metal Parts and Tooling [Member] Represents information pertaining to metal parts and tooling. Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Series 2020B Senior Unsecured Notes Senior Unsecured Notes 3.22%, Series B, Due August 20, 2030 [Member] Senior Unsecured Notes 3.22%, Series B, Due August 20, 2030 Debt instrument, basis spread on variable rate (as a percent) Debt Instrument, Basis Spread on Variable Rate City Area Code City Area Code Restricted Stock Awards Restricted Stock Settled Awards Restricted Stock [Member] Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] All Individuals All Individuals [Member] Amounts to be refunded to customers Public Utilities, Interim Rate Refunds Public Utilities, Interim Rate Refunds DPP Settlement Agreement DPP Settlement Agreement [Member] DPP Settlement Agreement Dividends Paid Payments of Dividends Pension Benefit Liability Liability, Defined Benefit Pension Plan, Noncurrent Name Forgone Recovery, Individual Name Finished Goods Inventory, Finished Goods, Net of Reserves Regulatory Liability [Domain] Regulatory Liability [Domain] Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Weighted-Average Grant-Date Fair Value Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Statement [Line Items] Statement [Line Items] Total Noncurrent Assets Assets, Noncurrent Total Assets Identifiable Assets Assets Megawatt hours of electricity Derivative, Nonmonetary Notional Amount, Energy Measure Entity [Domain] Entity [Domain] Schedule of Defined Benefit Plans Disclosures [Table] Defined Benefit Plan [Table] Discrete income tax benefits related to losses recognized from settlement agreements Tax Adjustments, Settlements, and Unusual Provisions Amortization of Prior Service Cost Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Schedule of Share-Based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions Schedule of Share-Based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block] Operating Segments Operating Segments [Member] Pension and Other Postretirement Benefits, net of tax benefit of $0, $4, $0 and $8 Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax and Reclassification Adjustment, Attributable to Parent Interest Expense Interest Expense Interest Expense, Nonoperating Gross Unrealized Gains Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax Share-Based Payments Share-Based Payment Arrangement [Text Block] Other Comprehensive Income Before Reclassifications, net of tax OCI, before Reclassifications, Net of Tax, Attributable to Parent Otter Tail Power Company Otter Tail Power Company [Member] Represents information about Otter Tail Power Company. Other Assets Increase (Decrease) in Other Operating Assets PEO PEO [Member] Accrued Taxes Accrual for Taxes Other than Income Taxes, Current Share-based payment arrangement, expense Share-Based Payment Arrangement, Expense Nonelectric Property, Plant and Equipment Property, Plant and Equipment, Nonelectric Property, Plant and Equipment, Nonelectric Measurement Basis [Axis] Measurement Basis [Axis] Series 2025A Senior Unsecured Notes Senior Unsecured Notes 5.49%, Series A, Due March 27, 2035 [Member] Senior Unsecured Notes 5.49%, Series A, Due March 27, 2035 Other Noncurrent Liabilities Other Liabilities, Noncurrent Goodwill Goodwill Retirement Plan Type [Axis] Retirement Plan Type [Axis] Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Total Investments Investments Granted (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Due in one year or less Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Subsequent Event Type [Domain] Subsequent Event Type [Domain] Retained Earnings Retained Earnings [Member] Asset Retirement Obligations Asset Retirement Obligation Disclosure [Text Block] Forfeited (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Net Unrealized Gains (Losses) on Available-for-Sale Securities AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Parent [Member] Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Debt to total capitalization ratio Debt To Total Capitalization Ratio Represents the required ratio of debt to total capitalization. Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Common stock, shares outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Award Timing Disclosures [Line Items] Schedule of Fair Value of Assets and Liabilities Fair Value, by Balance Sheet Grouping [Table Text Block] Corporate Debt Securities Corporate Debt Securities [Member] Diluted (in dollars per share) Earnings Per Share, Diluted Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Entity Current Reporting Status Entity Current Reporting Status Series 2020D Senior Unsecured Notes Senior Unsecured Notes 3.92%, Series D, Due February 25, 2050 [Member] Senior Unsecured Notes 3.92%, Series D, Due February 25, 2050 Net Cash Provided by (Used in) Financing Activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Total Shareholder Return Amount Total Shareholder Return Amount Liabilities: Liabilities, Fair Value Disclosure [Abstract] Litigation Case [Domain] Litigation Case [Domain] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Plant Removal Obligations Plant Removal Obligations [Member] Plant Removal Obligations Electric Operating and Maintenance Expenses Operating and Maintenance Expenses Utilities Operating Expense, Maintenance and Operations Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Share-Based Payment Arrangement [Abstract] Net Nonelectric Property, Plant and Equipment Property, Plant, and Equipment, after Accumulated Depreciation, Depletion, and Amortization Financing Activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Total Operating Revenues Operating Revenue Revenue from Contract with Customer, Excluding Assessed Tax Fuel Clause Adjustments Fuel Clause Adjustment [Member] Fuel Clause Adjustment Amount Available Line of Credit Facility, Remaining Borrowing Capacity Letters of Credit Line of Credit, Current Interest Cost Defined Benefit Plan, Interest Cost Schedule of Investments Investment [Table Text Block] Restricted Cash Settled Awards Restricted Cash Settled Awards [Member] Restricted Cash Settled Awards Financial Instruments [Domain] Financial Instruments [Domain] Alternative Revenue Program Riders Alternative Revenue Program Riders [Member] Alternative Revenue Program Riders Total Derivative Assets Derivative Instruments Derivative Asset Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Additions Charged to Expense Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease) Underlying Securities Award Underlying Securities Amount Fair Value Estimate of Fair Value Measurement [Member] Revenue Revenue from Contract with Customer [Text Block] Raw Material, Fuel and Supplies Inventory, Raw Materials and Supplies, Net of Reserves Inventories Increase (Decrease) in Inventories Cliff awards vesting period (in years) Share-based Compensation Arrangement by Share-based Payment Award, Award Cliff Vesting Period Share-based Compensation Arrangement by Share-based Payment Award, Award Cliff Vesting Period Schedule of Nonvested Restricted Stock Shares Activity Nonvested Restricted Stock Shares Activity [Table Text Block] Number of shares available for grant (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant Segment Reporting [Table] Segment Reporting [Table] Sale of Stock [Axis] Sale of Stock [Axis] Other Current Assets Other Assets, Current Equity to total capitalization ratio Equity To Total Capitalization Ratio Represents the ratio of Equity to total capitalization, which includes as equity minority interest and preferred stock as well as all of the components of common equity as presented on the balance sheet. Total capitalization is calculated as equity plus short-term debt plus long-term debt as presented on the balance sheet. Commitments and Contingencies Disclosure [Abstract] All Trading Arrangements All Trading Arrangements [Member] Gain (loss) on derivatives, net Derivative, Gain (Loss) on Derivative, Net Other Performance Measure, Amount Other Performance Measure, Amount Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Total Gross Electric Plant Public Utilities, Property, Plant and Equipment, Gross Public Utilities, Property, Plant and Equipment, Gross Operating Income (Loss) Operating Income (Loss) Current Fiscal Year End Date Current Fiscal Year End Date Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount OTP Credit Agreement OTP Credit Agreement [Member] Represents information about OTP credit agreement. Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Earnings Per Share, Diluted, by Common Class, Including Two-Class Method [Table] Common Dividends (in dollars per share) Common Stock, Dividends, Per Share, Declared Entity File Number Entity File Number Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Service Cost Defined Benefit Plan, Service Cost Net Repayments of Short-Term Debt Proceeds from (Repayments of) Short-Term Debt Stock Issued Under Share-Based Compensation Plans, net of shares withheld for employee taxes Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture Schedule of Investments Classified by Contractual Maturity Date Investments Classified by Contractual Maturity Date [Table Text Block] Production Fuel and Purchased Power Utilities Operating Expense, Fuel Used and Purchase Power Utilities Operating Expense, Fuel Used and Purchase Power Property, Plant and Equipment, net of accumulated depreciation Total Net Property, Plant and Equipment Property, Plant and Equipment, Net Including Public Utilities Property, Plant and Equipment, Net Including Public Utilities Supplemental Balance Sheet [Line Items] Supplemental Balance Sheet [Line Items] Supplemental Balance Sheet [Line Items] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Measure: Measure [Axis] Estimated fair value of liability Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Nonvested Series 2013A Senior Unsecured Notes Senior Unsecured Notes 4.68%, Series A, Due February 27, 2029 [Member] Represents information about Senior Unsecured Notes 4.68%, Series A, due February 27, 2029. Asset retirement obligations, noncurrent Asset Retirement Obligations, Noncurrent Requested equity ratio, percent (as a percent) Public Utilities, Requested Equity Ratio, Percentage Public Utilities, Requested Equity Ratio, Percentage Total Short-term Investments Debt Securities, Available-for-Sale, Current Accumulated Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] Cost of Products Sold (excluding depreciation) Cost of Goods and Service, Excluding Depreciation, Depletion, and Amortization Equity Components [Axis] Equity Components [Axis] EUP Settlement Agreement EUP Settlement Agreement [Member] EUP Settlement Agreement Product and Service [Domain] Product and Service [Domain] Class of Stock [Line Items] Class of Stock [Line Items] Pension and Other Postretirement Benefit Plans Pension and Other Postretirement Benefit Plans [Member] Pension and Other Postretirement Benefit Plans Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Capitalization Capitalization, Long-Term Debt and Equity [Abstract] Entity Interactive Data Current Entity Interactive Data Current Deferred Income Taxes Deferred Income Taxes [Member] Represents information about deferred income taxes. Deferred Income Taxes Deferred Income Tax Liabilities, Net Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Entity Small Business Entity Small Business Electric Plant in Service Public Utilities, Property, Plant and Equipment, Plant in Service Total Comprehensive Income (Loss) Comprehensive Income (Loss), Net of Tax, Attributable to Parent Unamortized Long-Term Debt Issuance Costs Debt Instrument, Unamortized Discount Supplemental Balance Sheet [Table] Supplemental Balance Sheet [Table] Supplemental Balance Sheet [Table] Termination Date Trading Arrangement Termination Date Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Other Current Liabilities Other Liabilities, Current Other Noncurrent Assets Other Assets, Noncurrent Document Type Document Type 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] Other Current Assets Derivative Asset, Current Reduction in estimated ARO liabilities Asset Retirement Obligation, Period Increase (Decrease) Fair Value as of Grant Date Award Grant Date Fair Value Debt instrument, redemption price, percentage (as a percent) Debt Instrument, Redemption Price, Percentage Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Arrangement Duration Trading Arrangement Duration Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Proceeds from Issuance of Long-Term Debt Proceeds from Issuance of Long-Term Debt Local Phone Number Local Phone Number Postretirement Benefits Other Postretirement Benefits Plan [Member] Consolidation Items [Axis] Consolidation Items [Axis] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Registrant Name Entity Registrant Name Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Schedule of Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities [Table Text Block] Schedule of Regulatory Assets and Liabilities Commitments and Contingencies (Note 10) Commitments and Contingencies Total Operating Revenues from Contracts with Customers Revenues Total Gross Nonelectric Property, Plant and Equipment Property, Plant, and Equipment, before Accumulated Depreciation, Depletion, and Amortization Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Electric Electric Electric [Member] Represents information about Electric segment. Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Executive Category: Executive Category [Axis] Award vesting period (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period OTC Credit Agreement Otter Tail Corporation Credit Agreement [Member] Represents information about the Otter Tail Corporation Credit Agreement. Liabilities and Shareholders' Equity Liabilities and Equity [Abstract] Other Commitments [Table] Other Commitments [Table] Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Inventories Total Inventories Inventory, Net Award Type [Domain] Award Type [Domain] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Fair Value Measurements Fair Value Disclosures [Text Block] Level 3 Fair Value, Inputs, Level 3 [Member] Expected term (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Term Debt instrument, redemption price, percentage of principal amount redeemed (as a percent) Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed Initial term Lessee, Operating Lease, Term of Contract PEO Name PEO Name Restricted Cash Restricted Cash Nonservice Components of Postretirement Benefits Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component Long-Lived Asset, Class [Axis] Long-Lived Asset, Class [Axis] Other Segment Items Segment Reporting, Other Segment Item, Amount Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Entity Tax Identification Number Entity Tax Identification Number Derivative Instruments and Hedging Activities Disclosures [Table] Derivative Instruments and Hedging Activities Disclosures [Table] Legal Entity [Axis] Legal Entity [Axis] Series 2020C Senior Unsecured Notes Senior Unsecured Notes 3.62%, Series C, Due February 25, 2040 [Member] Senior Unsecured Notes 3.62%, Series C, Due February 25, 2040 Accounts Receivable, Allowance for Credit Loss [Roll Forward] Accounts Receivable, Allowance for Credit Loss [Roll Forward] Debt Securities Debt Securities, Available-for-Sale, Noncurrent Other Commitments [Line Items] Other Commitments [Line Items] North Dakota PTC Refunds North Dakota PTC Refunds [Member] North Dakota PTC Refunds Public utilities, requested equity capital structure (as a percent) Public Utilities, Requested Equity Capital Structure, Percentage Cash, Cash Equivalents and Restricted Cash at Beginning of Period Cash, Cash Equivalents and Restricted Cash at End of Period Total Cash, Cash Equivalents and Restricted Cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Accounts Payable Increase (Decrease) in Accounts Payable Schedule of Change in Asset Retirement Obligations Schedule of Change in Asset Retirement Obligation [Table Text Block] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Number of performance measures Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Performance Measures Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Performance Measures Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Non-NEOs Non-NEOs [Member] Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Debt Instrument [Axis] Debt Instrument [Axis] Stock Compensation Expense Share-Based Payment Arrangement, Noncash Expense Shelf registration (in shares) Shelf Registration, Shares Shelf registration for issuance of common shares Public Utilities, Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] Fuel Clause Adjustments Fuel Clause Adjustments [Member] Fuel Clause Adjustments Schedule of Debt Schedule of Debt [Table Text Block] Schedule of Inventories Schedule of Inventory, Current [Table Text Block] Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Basic (in dollars per share) Earnings Per Share, Basic Schedule of Share-based Compensation Arrangements by Share-based Payment Award Disclosure of Share-Based Compensation Arrangements by Share-Based Payment Award [Table Text Block] Total Current Assets Assets, Current Statistical Measurement [Axis] Statistical Measurement [Axis] Insider Trading Arrangements [Line Items] Short-Term Debt Short-Term Debt, Fair Value Second Shelf Registration Second Shelf Registration [Member] Second Shelf Registration Award Type [Axis] Award Type [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Retained Earnings Retained Earnings (Accumulated Deficit) Product and Service [Axis] Product and Service [Axis] Mutual Funds Equity Securities, FV-NI Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Pension Benefits (Pension Plan) Pension Plan [Member] Common Shares Common Stock [Member] Approved return on base rate, percent (as a percent) Public Utilities, Approved Return On Rate Base, Percentage Public Utilities, Approved Return On Rate Base, Percentage Fair Value Total Debt Securities Debt Securities, Available-for-Sale Fair Value Measurement [Domain] Fair Value Measurement [Domain] Expected volatility Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Volatility Rate Electric Production Fuel Utilities Operating Expense, Fuel Used Other Other Regulatory Liabilities [Member] Other Regulatory Liabilities Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Cover [Abstract] Cover [Abstract] Dividend yield Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Dividend Rate Series 2019B Senior Unsecured Notes Senior Unsecured Notes 3.52%, Series B, Due October 10, 2039 [Member] Related to debt. Construction Work in Progress Property, Plant and Equipment, Construction Work in Progress Property, Plant and Equipment, Construction Work in Progress Derivative Contract [Domain] Derivative Contract [Domain] Electric Plant Public Utilities, Property, Plant and Equipment, Net [Abstract] SDPUC SDPUC [Member] SDPUC Equity Awards Adjustments Equity Awards Adjustments [Member] Other Noncurrent Liabilities Derivative Liability, Noncurrent Total Liabilities and Shareholders' Equity Liabilities and Equity Regulatory Asset [Domain] Regulatory Asset [Domain] Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Employee Stock Purchase Plan Share-Based Payment Arrangement, Option [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Asset retirement obligation, current Asset Retirement Obligation, Current Construction Work in Progress Public Utilities, Property, Plant and Equipment, Construction Work in Progress Corporate-Owned Life Insurance Policies Life Insurance, Corporate or Bank Owned, Amount Segments [Axis] Segments [Axis] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Schedule of Receivables Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Tabular List, Table Tabular List [Table Text Block] Mutual Funds Equity Securities, FV-NI, Noncurrent Other Income (Expense), net Other Nonoperating Income (Expense) Number of regional transmission organizations with show cause proceedings Number Of Regional Transmission Organizations With Show Cause Proceedings Number Of Regional Transmission Organizations With Show Cause Proceedings Accrued Accretion Asset Retirement Obligation, Accretion Expense Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] Name Awards Close in Time to MNPI Disclosures, Individual Name Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period Noncurrent Assets Assets, Noncurrent [Abstract] Long-Lived Asset, Class [Domain] Long-Lived Asset, Class [Domain] Adjustment to Compensation: Adjustment to Compensation [Axis] Other Other Receivables, Gross, Current Series 2026B Senior Unsecured Notes Senior Unsecured Notes 6.04%, Series B, Due June 04, 2056 [Member] Senior Unsecured Notes 6.04%, Series B, Due June 04, 2056 Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Capital Expenditures Payments to Acquire Productive Assets Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Series 2024A Senior Unsecured Notes Senior Unsecured Notes 5.48%, Series A, Due April 01, 2034 [Member] Senior Unsecured Notes 5.48%%, Series A, Due April 01, 2034 Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Total Assets Assets, Fair Value Disclosure Regulatory Matters Schedule of Regulatory Assets and Liabilities [Text Block] Wholesale Wholesale [Member] Sale of product through wholesale purchases. Name Measure Name Income Taxes Income Tax Disclosure [Text Block] Accounts Payable Accounts Payable, Current Pay vs Performance Disclosure [Line Items] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Other, Net Other Noncash Income (Expense) Debt Instrument [Line Items] Debt Instrument [Line Items] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Additional Paid-In Capital Additional Paid-in Capital [Member] Entity Filer Category Entity Filer Category Investments Short-Term Investments Electric Segment - ARP Revenues Revenue Not from Contract with Customer Name Trading Arrangement, Individual Name Cash and Cash Equivalents Cash and Cash Equivalent Requested rate increase, percent (as a percent) Public Utilities, Requested Rate Increase (Decrease), Percentage Company Selected Measure Amount Company Selected Measure Amount Investments, Debt and Equity Securities [Abstract] Depreciation and Amortization Depreciation and Amortization Depreciation and Amortization Depreciation, Depletion and Amortization Entity Address, Address Line Two Entity Address, Address Line Two Stock Issued Under Share-Based Compensation Plans, net of shares withheld for employee taxes (in shares) Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture Schedule of Stock by Class [Table] Stock, Class of Stock [Table] Minnesota Rate Case Minnesota Rate Case [Member] Minnesota Rate Case Current Assets Assets, Current [Abstract] Total Derivative Liabilities Derivative Liability Non-PEO NEO Non-PEO NEO [Member] Senior Notes Senior Notes [Member] Entity Address, Address Line One Entity Address, Address Line One Right-of-use asset obtained in exchange for operating lease liability Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Vested (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Income Tax (Benefit) Expense Income Tax Expense (Benefit) Income Tax Expense (Benefit) Cost of Goods Sold Cost of Product and Service Sold Regulatory Assets Increase (Decrease) in Other Regulatory Assets Award Timing Method Award Timing Method [Text Block] Net Change in Cash, Cash Equivalents and Restricted Cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Pension Benefits (ESSRP) Executive Survivor and Supplemental Retirement Plan [Member] Represents information about executive survivor and supplemental retirement plan. Amortization of Net Actuarial Loss Defined Benefit Plan, Amortization of Gain (Loss) Adjustments Due to Revisions in Cash Flow Estimates Asset Retirement Obligation, Revision of Estimate AOCI Attributable to Parent, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Net Income (Loss) Net Income (Loss) Net Income Net Income (Loss) Attributable to Parent Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Statement [Table] Statement [Table] Restatement Determination Date: Restatement Determination Date [Axis] Regulatory Liabilities Regulatory liabilities, current Regulatory Liability, Current Schedule of Changes in Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Litigation settlement, amount paid Litigation Settlement, Amount Awarded to Other Party Derivative Instruments and Hedging Activities Disclosures [Line Items] Derivative Instruments and Hedging Activities Disclosures [Line Items] Receivables Increase (Decrease) in Receivables Operating Revenues Revenues [Abstract] Plastic Products and Tooling Plastic Products [Member] Represents information pertaining to plastic products. Other Postretirement Benefits Liability Liability, Other Postretirement Defined Benefit Plan, Noncurrent Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract]