Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Follow-On Public Stock Offering Follow-On Public Stock Offering [Member] Public Stock Offering Natural gas costs recoverable through rate adjustments Asset Recoverable Gas Costs [Member] 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] Title of 12(b) Security Title of 12(b) Security Carrying amount Reported Value Measurement [Member] Debt Securities, Available-for-Sale [Table] Debt Securities, Available-for-Sale [Table] North Dakota NORTH DAKOTA Document Fiscal Year Focus Document Fiscal Year Focus Percentage investment in target date investments Percentage Investment In Target Date Investments The percentage of insurance contracts in target date investments. Revenue, remaining performance obligation, expected timing of satisfaction, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Adjustment to Compensation, Amount Adjustment to Compensation Amount Schedule of available-for-sale securities, major types of debt and equity securities [Axis] Financial Instrument [Axis] Customer [Axis] Customer [Axis] Segment Reporting [Abstract] Segment Reporting [Abstract] Accumulated deferred investment tax credit Accumulated Deferred ITC [Member] Accumulated Deferred ITC Net settlement shares for counterparty if FSAs were settled Sale of Stock, Consideration Received on Transaction, Entitled Net Settlement For Counterparty, Number Of Shares Sale of Stock, Consideration Received on Transaction, Entitled Net Settlement For Counterparty, Number Of Shares Tax withholding on stock-based compensation Payment, Tax Withholding, Share-Based Payment Arrangement Montana MONTANA Accrued compensation Employee-related Liabilities, Current Interest expense Disposal Group, Including Discontinued Operation, Interest Expense Schedule of Long-Term Debt Outstanding Schedule of Long-Term Debt Instruments [Table Text Block] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Employee benefit plans Retirement Benefits [Text Block] Potential liabilities related to litigation and environmental matters Loss Contingency Accrual Line of Credit Line of Credit [Member] Restatement Determination Date Restatement Determination Date Expected return on assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Cash Paid, TSA Cash Paid, TSA [Member] Cash Paid for TSA Other Other Revenues [Member] Other revenues from disaggregation by customer or product and service. Beginning balance Ending balance Accounts Receivable, Allowance for Credit Loss Regulatory liabilities Regulatory Liability, Noncurrent Amendment Flag Amendment Flag Consolidated Entities [Axis] Consolidated Entities [Axis] Current liabilities: Liabilities, Current [Abstract] Provision for credit losses Current expected credit loss provision Accounts Receivable, Credit Loss Expense (Reversal) Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Disposal Group Classification [Axis] Disposal Group Classification [Axis] Gross Unrealized Losses Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax Schedule of Available-for-Sale Securities Debt Securities, Available-for-Sale [Table Text Block] Loss Contingencies [Table] Loss Contingencies [Table] Loss contingency, regulatory asset Loss Contingency, Regulatory Asset Loss Contingency, Regulatory Asset Other comprehensive income: Other Comprehensive Income (Loss), Net of Tax [Abstract] Percentage in fixed-income and other investments Percentage In Fixed-Income And Other Investments The percentage of insurance contracts in fixed-income and other investments. Discontinued Operations, Disposed of by Means Other than Sale, Spinoff Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member] Total noncurrent liabilities  Liabilities, Noncurrent Estimated Recovery or Refund Period Regulatory Asset, Amortization Period Natural gas storage Natural Gas, Storage [Member] Consolidated Entities [Domain] Consolidated Entities [Domain] Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Percentage investment in international investments Percentage Investment In International Investments Percentage of insurance contracts in international investments. Postretirement liability adjustment: Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax [Abstract] Entity Address, State or Province Entity Address, State or Province Provisions for Increased Borrowings, up to a maximum of: Line of Credit Facility, Maximum Available Capacity Increase The option to increase borrowing capacity to the stated maximum amount, at the option of the company, on stated conditions. PEO Total Compensation Amount PEO Total Compensation Amount Loss contingency, receivable Loss Contingency, Receivable Common stock, par value per share (in usd per share) Common Stock, Par or Stated Value Per Share Noncurrent liabilities: Liabilities, Noncurrent [Abstract] Weighted average common shares outstanding - basic (in shares) Weighted Average Number of Shares Outstanding, Basic Retirement Benefits [Abstract] Retirement Benefits [Abstract] 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] Regulatory assets Regulatory Asset, Noncurrent Variable Interest Entities [Line Items] Loss Contingencies [Line Items] Cost recovery mechanisms Regulatory Clause Revenues, under-Recovered [Member] Total current liabilities  Liabilities, Current Regulatory Liability [Axis] Regulatory Liability [Axis] Taxes, other than income Taxes, Miscellaneous Aggregate gross sales price Sale Of Stock, Available Capacity, Aggregate Gross Sales Price Sale Of Stock, Available Capacity, Aggregate Gross Sales Price Year Two Year Two [Member] Year Two Other noncurrent changes Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net Entity Address, City or Town Entity Address, City or Town Cascade Natural Gas Corporation Cascade Natural Gas Corporation [Member] Information on Cascade Natural Gas Corporation, an indirect wholly owned subsidiary of MDU Energy Capital, which is a direct wholly owned subsidiary of the Company. Defined benefit plan disclosure, net periodic benefit cost [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] Less amount capitalized Defined Benefit Plan Net Periodic Benefit Cost Amount Capitalized The total amount of net periodic benefit cost for defined benefit plans capitalized for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain or loss, prior service cost or credit, transition asset or obligation, and gain or loss due to settlements or curtailments). Basis of presentation Basis of Accounting, Policy [Policy Text Block] Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Receivable [Domain] Receivable [Domain] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Facility Limit Line of credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Other comprehensive income Other comprehensive income Other Comprehensive Income (Loss), Net of Tax Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Contract With Customer [Domain] Contract With Customer [Domain] Contract With Customer [Domain] Long-term debt due within one year Less current maturities Long-Term Debt, Current Maturities Credit Agreement Expiring October 2028 Credit Agreement Expiring October 2028 [Member] Credit Agreement Expiring October 2028 Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Net cash provided by continuing operations Cash Provided by (Used in) Operating Activity, Continuing Operation Estimated Recovery or Refund Period Regulatory Liability, Amortization Period Manufactured gas plant site remediation Environmental Restoration Costs [Member] Earnings per share Earnings Per Share, Policy [Policy Text Block] New accounting standards New Accounting Pronouncements, Policy [Policy Text Block] Property, plant and equipment additions in accounts payable Capital Expenditures Incurred but Not yet Paid Segment Reporting Segment Reporting [Table Text Block] Amortization of debt issuance costs Amortization of Debt Issuance Costs Schedule of Regulatory Liabilities Schedule of Regulatory Liabilities [Table Text Block] Long-term debt Total long-term debt Long-Term Debt Guarantor Obligations [Line Items] Guarantor Obligations [Line Items] Document Period End Date Document Period End Date Changes in current assets and liabilities, net of acquisitions: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] South Dakota SOUTH DAKOTA Plant costs/asset retirement obligations Asset Retirement Obligation Costs [Member] 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] Fuel contract Fuel contract [Member] Fuel contract. Debt instrument, face amount Debt Instrument, Face Amount Total regulatory assets Regulatory Asset Equity Equity [Text Block] Earnings per share - basic: Earnings per share - basic: Earnings Per Share, Basic [Abstract] Security Exchange Name Security Exchange Name Schedule of Reconciliation of Revenue from Segments to Consolidated Segment Reporting, Reconciliation of Revenue by Segment to Consolidated [Table Text Block] Net unrealized (loss) gain on available-for-sale investments arising during the period, tax OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax Contract with customer, term Contract With Customer, Term Contract With Customer, Term Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Entity Shell Company Entity Shell Company Consolidation Items [Domain] Consolidation Items [Domain] Tax benefit, change in tax method Discontinued Operations, Tax Effect Of Election For A Change In Tax Method Discontinued Operations, Tax Effect Of Election For A Change In Tax Method Schedule of Accounts Receivable, Allowance for Credit Loss Accounts Receivable, Allowance for Credit Loss [Table Text Block] Business segment data Segment Reporting, Policy [Policy 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] Earnings Per Share [Abstract] Reclassification adjustment for loss on available-for-sale investments included in net income, tax Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Credit Agreement Expiring May 2028 Credit Agreement Expiring May 2028 [Member] Credit Agreement Expiring May 2028 Schedule of Weighted Average Common Shares Outstanding Schedule of Weighted Average Number of Shares [Table Text Block] Document Fiscal Period Focus Document Fiscal Period Focus Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Trading Symbol Trading Symbol Variable interest entities Consolidation, Variable Interest Entity, Policy [Policy Text Block] Public utilities, interim rate increase (decrease), 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] Amount suspended Loss Contingency, Amount Suspended Loss Contingency, Amount Suspended Oregon OREGON Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Environmental allowances and obligations Environmental Allowance and Obligations [Text Block] Environmental Allowance and Obligations Electric fuel and purchased power Utilities Operating Expense, Purchased Power Annual Revenue Increase (in millions), approved Public Utilities, Approved Rate Increase (Decrease), Amount Financing Receivable, Allowance for Credit Loss [Line Items] Financing Receivable, Allowance for Credit Loss [Line Items] Discontinued operation, amount of continuing cash flows after disposal Discontinued Operation, Continuing Cash Inflow (Outflow) after Disposal, Amount Company Selected Measure Name Company Selected Measure Name Sale of Stock [Domain] Sale of Stock [Domain] Number Of Reportable Segments Not Disclosed Flag Number Of Reportable Segments Not Disclosed Flag Number Of Reportable Segments Not Disclosed Flag Net unrealized (loss) gain on available-for-sale investments OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax Regulated Operation, Regulatory Asset [Table] Regulated Operation, Regulatory Asset [Table] Earnings per share - diluted: Earnings per share - diluted: Earnings Per Share, Diluted [Abstract] Discontinued operations, net of tax (in usd per share) Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share Medium-Term Notes Medium-Term Note [Member] Long-term debt, gross Long-Term Debt, Gross Credit Facility [Domain] Credit Facility [Domain] Operating activities: Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Compensation Amount Outstanding Recovery Compensation Amount Dividends payable Dividends Payable, Current Individual: Individual [Axis] Weighted average common shares outstanding - diluted (in shares) Weighted average common shares outstanding - diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Public Utility [Axis] Public Utility [Axis] Stock issued if FSAs were settled (in shares) Stock Issued During Period, Shares, New Issues, If Forward Sale Agreements Were Settled Stock Issued During Period, Shares, New Issues, If Forward Sale Agreements Were Settled Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Environmental allowances Environmental Allowances, Noncurrent Environmental Allowances, Noncurrent Entity Emerging Growth Company Entity Emerging Growth Company Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] Taxes recoverable from customers Deferred Income Tax Charge [Member] General Rate Cases Pending Pending Rate Case [Member] Pending Rate Case [Member] Disposal Group Name [Domain] Disposal Group Name [Domain] Line of Credit Facility [Table] Line of Credit Facility [Table] Credit Loss [Abstract] Credit Loss [Abstract] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Commercial Paper Commercial Paper [Member] U.S. Treasury securities US Treasury Securities [Member] Regulatory Asset [Axis] Regulatory Asset [Axis] Credit Agreement Expiring June 2029 Credit Agreement Expiring June 2029 [Member] Credit Agreement Expiring June 2029 Schedule of Pretax Income (Loss) From Discontinued Operations Disposal Groups, Including Discontinued Operations [Table Text Block] Variable interest entity, reporting entity involvement, maximum loss exposure, amount Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Effect of dilutive performance share awards and restricted stock units (in shares) Weighted Average Number of Shares Outstanding, Diluted, Adjustment Natural gas costs refundable through rate adjustments Liabilities Refundable Gas Costs [Member] Carrying amount as of the balance sheet date of gas costs of a regulated entity that are refundable through future rate adjustments within one year of the balance sheet date or the normal operating cycle, if longer Percentage investment in real estate Percentage Investment In Real Estate Percentage Investment In Realestate Award Timing Predetermined Award Timing Predetermined [Flag] Ratio of total debt to total capitalization Debt Covenant, Funded Debt To Total Capitalization, Ratio Debt Covenant, Funded Debt To Total Capitalization, Ratio Letters of credit at end of period Outstanding letters of credit Letters of Credit Outstanding, Amount Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-Sale [Line Items] Net cash provided by (used in) discontinued operations Cash Provided by (Used in) Operating Activity, Discontinued Operation Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Revenue from contract with customer, term of contract Contract With Customer, Weighted Average Remaining Duration Contract With Customer, Weighted Average Remaining Duration Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] Other income Disposal Group, Including Discontinued Operation, Other Income Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Environmental allowances and obligations Emission Credits or Allowances, Policy [Policy Text Block] Investment withdrawal, percentage Life Insurance, Corporate or Bank Owned, Cash Withdrawn, Percentage Life Insurance, Corporate or Bank Owned, Cash Withdrawn, Percentage Fair value measurements Fair Value of Financial Instruments, Policy [Policy Text Block] Natural gas distribution Natural Gas Distribution Natural Gas Distribution [Member] This segment distributes natural gas in Montana, North Dakota, South Dakota, Wyoming, Idaho, Minnesota, Oregon and Washington. These operations also supply related value-added services. Debt Securities, Available-for-sale [Abstract] Debt Securities, Available-for-Sale [Abstract] All Executive Categories All Executive Categories [Member] Washington WASHINGTON Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Long-term debt, fair value Long-Term Debt, Fair Value Schedule of Net Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Scenario [Domain] Scenario [Domain] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Annual Revenue Increase (%), approved Public Utilities, Approved Rate Increase (Decrease), Percentage Debt Disclosure [Abstract] Debt Disclosure [Abstract] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Business segment data Segment Reporting [Text Block] Amount outstanding, end of period Long-Term Line of Credit Minimum Minimum [Member] Expiration Date Trading Arrangement Expiration Date Increase (decrease) in cash, cash equivalents and restricted cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Excluding Exchange Rate Effect, Including Discontinued Operation Pipeline Pipeline [Member] This segment provides natural gas transportation, underground storage, processing and gathering services, as well as oil gathering, through regulated and nonregulated pipeline systems primarily in the Rocky Mountain and northern Great Plains regions of the United States. Schedule of Disaggregation of revenue Disaggregation of Revenue [Table Text Block] Income from continuing operations (in usd per share) Income (Loss) from Continuing Operations, Per Diluted Share Income from continuing operations (in usd per share) Income (Loss) from Continuing Operations, Per Basic Share Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Assets: Cash and Cash Equivalents, Fair Value Disclosure 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] Disposal Group, Including Discontinued Operations [Line Items] Disposal Group, Including Discontinued Operations [Line Items] Annual Revenue Increase (in millions), pending Public Utilities, Requested Rate Increase (Decrease), Amount Net periodic benefit credit Net periodic benefit cost (credit) Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Operating expenses Disposal Group, Including Discontinued Operation, Operating Expense Issuance of common stock, net Proceeds from Issuance of Common Stock Financing Receivable, Allowance for Credit Loss [Roll Forward] Financing Receivable, Allowance for Credit Loss [Table] Common stock, authorized (in shares) Common Stock, Shares Authorized Sale of stock, number of shares issued (in shares) Shares issued (in shares) Sale of Stock, Number of Shares Issued in Transaction 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] Proceeds from investment securities Proceeds from Sale and Maturity of Debt Securities, Available-for-Sale Document Quarterly Report Document Quarterly Report Lease receivables Lessor, Operating Lease, Payment to be Received, Year One Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] 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 assets not earning a rate of return Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided Current environmental allowances Environmental Allowances, Current Environmental Allowances, Current Debt Debt Disclosure [Text Block] Scenario [Axis] Scenario [Axis] Repayment of long-term debt Repayments of long-term debt Repayments of Long-Term Debt Operating Activities [Domain] Operating Activities [Domain] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Regulatory Assets and Liabilities Disclosure [Abstract] Regulatory Assets and Liabilities Disclosure [Abstract] Less unamortized debt issuance costs Debt Issuance Costs, Net Contract With Customer [Axis] Contract With Customer [Axis] Contract With Customer 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 Sale of stock, cash received Net proceeds Sale of Stock, Consideration Received on Transaction At The Market Offering At The Market Offering [Member] At The Market Offering Adoption Date Trading Arrangement Adoption Date Inventories and natural gas in storage Inventory, Policy [Policy Text Block] Interest rate, stated percentage Debt Instrument, Interest Rate, Stated Percentage Dividends declared on common stock Dividends, Common Stock, Cash Total stockholders' equity Beginning balance Ending balance Equity, Attributable to Parent Residential utility sales Residential Utility Sales [Member] Residential Utility Sales [Member] Interim rate increase (%) pending Public Utilities, Interim Rate Increase (Decrease), Percentage Proposed depreciation rate increase (decrease) as percentage of revenue Proposed Depreciation Rate Increase (Decrease) As Percentage Of Revenue Proposed Depreciation Rate Increase (Decrease) As Percentage Of Revenue Intermountain Gas Company Intermountain Gas Company [Member] Intermountain Gas Company Assets Assets [Abstract] Title Trading Arrangement, Individual Title Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Cost Debt Securities, Available-for-Sale, Amortized Cost Accounting Policies [Abstract] Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Unrealized gains (losses) on investments, net of insurance proceeds Unrealized Gains (Losses) On Investments, Net Of Insurance Proceeds Unrealized Gains (Losses) On Investments, Net Of Insurance Proceeds ROE, pending Public Utilities, Requested Return on Equity, Percentage Issuance costs Payments of Stock Issuance Costs Insider Trading Policies and Procedures [Line Items] Fuel stock Energy Related Inventory, Other Fossil Fuel Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Schedule of Line of Credit Facilities Schedule of Line of Credit Facilities [Table Text Block] Deferred income taxes Deferred Income Tax Expense (Benefit) Operation and maintenance Selling, General and Administrative Expense Cash if FSAs were settled Sale of Stock, Consideration Received on Transaction, If Forward Sale Agreements Were Settled Sale of Stock, Consideration Received on Transaction, If Forward Sale Agreements Were Settled Current regulatory assets Regulatory Asset, Current Natural gas in storage noncurrent Inventory, Gas in Storage Underground, Noncurrent Commitments and contingencies Commitments and Contingencies Disclosure [Text Block] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Shares excluded from the calculation of diluted earnings per share (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Natural gas transportation Natural Gas Transportation [Member] Natural Gas Transportation [Member] Net unrealized (loss) gain on available-for-sale investments: OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment, Tax [Abstract] Entity Central Index Key Entity Central Index Key Common stock Authorized - 500,000,000 shares, $1.00 par value Shares issued - 210,349,456 at June 30, 2026, 204,331,170 at June 30, 2025 and 204,382,821 at December 31, 2025 Common Stock, Value, Outstanding Less accumulated depreciation and amortization Property, Plant, and Equipment, Accumulated Depreciation, Depletion, and Amortization Other paid-in capital Additional Paid in Capital, Common Stock All Adjustments to Compensation All Adjustments to Compensation [Member] Other revenue Segment Reporting, Reconciling Item, Corporate Nonsegment [Member] Net settlement amount for counterparty if FSAs were settled Sale of Stock, Consideration Received on Transaction, Entitled Net Settlement For Counterparty, Amount Sale of Stock, Consideration Received on Transaction, Entitled Net Settlement For Counterparty, Amount Guarantor Obligation [Table] Guarantor Obligation [Table] Accumulated comprehensive loss 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] Separation related costs Restructuring and Related Cost, Incurred Cost Net cash provided by operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation WBI Energy Transmission WBI Energy Transmission [Member] WBI Energy Transmission Firm Storage Contract Firm Storage Contract [Member] Firm Storage Contract Stockholders' equity: Equity, Attributable to Parent [Abstract] Income Statement [Abstract] Income Statement [Abstract] Document Transition Report Document Transition Report Fair value, hierarchy [Axis] Fair Value Hierarchy and NAV [Axis] Operating expenses: Operating Expenses [Abstract] Intersegment eliminations Elimination of intersegment operating revenues Intersegment Eliminations [Member] Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Debt-to-Total Capitalization Ratio at June 30, 2026 Debt Instrument, Debt To Capitalization Ratio Debt Instrument, Debt To Capitalization Ratio City Area Code City Area Code Wyoming WYOMING Percentage investment in cash and cash equivalents Percentage Investment In Cash And Cash Equivalents Percentage of insurance contracts in cash and cash equivalents. Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] All Individuals All Individuals [Member] Dividends paid Payments of Dividends Name Forgone Recovery, Individual Name Pension and postretirement benefits Pension and Other Postretirement Plans Costs [Member] Commitments and contingencies Commitments and Contingencies, Policy [Policy Text Block] Regulatory Liability [Domain] Regulatory Liability [Domain] Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] General Rate Cases Finalized Finalized Rate Case [Member] Finalized Rate Case Statement [Line Items] Statement [Line Items] Total noncurrent assets  Assets, Noncurrent Total assets Assets Defined Benefit Plan [Table] Defined Benefit Plan [Table] Entity [Domain] Entity [Domain] New Accounting Pronouncements and Changes in Accounting Principles [Abstract] Accounting Standards Update and Change in Accounting Principle [Abstract] Amortization of prior service credit Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Total reportable segment operating revenues Operating Segments [Member] Interest expense Interest Expense, Nonoperating Current environmental obligations Accrued Environmental Loss Contingencies, Current Operating revenues Disposal Group, Including Discontinued Operation, Revenue Gross Unrealized Gains Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax Sale of stock, aggregate gross sales price, maximum Sale Of Stock, Aggregate Gross Sales Price, Maximum Sale Of Stock, Aggregate Gross Sales Price, Maximum Seasonality of operations Nature of Operations [Text Block] Issuance of common stock, net (in shares) Stock Issued During Period, Shares, New Issues PEO PEO [Member] Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Receivables and allowance for expected credit loss Credit Loss, Financial Instrument [Text Block] Schedule of ATM Offering Activity Schedule of Sale of Stock by Subsidiary or Equity Method Investee Disclosure [Table Text Block] Measurement Basis [Axis] Measurement Basis [Axis] Other 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 Income tax benefit Discontinued Operation, Tax Effect of Discontinued Operation Retained Earnings Retained Earnings [Member] Taxes payable Taxes Payable, Current Term Loan Agreement Term Loan Agreement [Member] Term Loan Agreement Total operating expenses Operating Expenses Revolving Credit Facility Revolving Credit Facility [Member] Money market funds Money Market Funds [Member] Cash Received, TSA Cash Received, TSA [Member] Cash Received from TSA Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Net unrealized (loss) gain on available-for-sale investments arising during the period, net of tax of $(10) and $4 for the three months ended and $(20) and $23 for the six months ended in 2026 and 2025, respectively OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax Award Timing Disclosures [Line Items] Schedule of Fair Value, by Balance Sheet Grouping Fair Value, by Balance Sheet Grouping [Table Text Block] Debt issuance costs Payments of Debt Issuance Costs Earnings per share - diluted (in usd per share) Earnings Per Share, Diluted Entity Current Reporting Status Entity Current Reporting Status Schedule of Regulatory Proceedings Public Utilities General Disclosures [Table Text Block] Net cash used in financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation MDU Resources Group, Inc. MDU Resources Group, Inc. [Member] MDU Resources Group, Inc. Total Shareholder Return Amount Total Shareholder Return Amount Unrealized gains on investments Unrealized Gain (Loss) on Investments Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] 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] Less write-offs charged against the allowance Accounts Receivable, Allowance for Credit Loss, Writeoff Revenues from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax Financing activities: Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Net property, plant and equipment Property, Plant, and Equipment, after Accumulated Depreciation, Depletion, and Amortization Line of credit facility, remaining borrowing capacity Line of Credit Facility, Remaining Borrowing Capacity Interest cost Defined Benefit Plan, Interest Cost Regulatory Assets Regulatory Asset [Line Items] Uncommitted Note Purchase And Private Shelf Agreement Uncommitted Note Purchase And Private Shelf Agreement [Member] Uncommitted Note Purchase And Private Shelf Agreement Major types of debt and equity securities [Domain] Financial Instruments [Domain] Amortization of postretirement liability losses included in net periodic benefit credit, net of tax of $50 and $33 for the three months ended and $85 and $51 for the six months ended in 2026 and 2025, respectively Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax Inventories and natural gas in storage Inventory Disclosure [Text Block] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Underlying Securities Award Underlying Securities Amount Fair value Estimate of Fair Value Measurement [Member] Revenue from contracts with customers Revenue from Contract with Customer [Text Block] Issuance of common stock, net Stock Issued During Period, Value, New Issues Over-Allotment Option Over-Allotment Option [Member] Other current liabilities Increase (Decrease) in Other Current Liabilities Amount of surety bonds outstanding Surety Bonds Outstanding Amount of surety bonds outstanding related to construction contracts and reclamation obligations. Inventories Increase (Decrease) in Inventories Segment Reporting [Table] Segment Reporting [Table] Sale of Stock [Axis] Sale of Stock [Axis] Prepayments and other current assets Other Assets, Current Weighted average interest rate Long-Term Debt, Weighted Average Interest Rate, at Point in Time Commitments and Contingencies Disclosure [Abstract] All Trading Arrangements All Trading Arrangements [Member] Other Performance Measure, Amount Other Performance Measure, Amount Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Operating income Operating Income (Loss) Remaining performance obligation, amount Revenue, Remaining Performance Obligation, Amount Current Fiscal Year End Date Current Fiscal Year End Date Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Rate Year [Domain] Rate Year [Domain] Rate Year [Domain] Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (in shares) Adjustments To Additional Paid In Capital, Stock Issued During Period, Shares, Treasury Stock Reissued Through Share-Based Payment Arrangement Adjustments To Additional Paid In Capital, Stock Issued During Period, Shares, Treasury Stock Reissued Through Share-Based Payment Arrangement 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] Dividends declared per common share (in usd 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 Electric Electric [Member] This segment generates, transmits and distributes electricity in Montana, North Dakota, South Dakota and Wyoming. These opeartions also supply related value-added services. Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Common stock, issued (in shares) Common stock, beginning balance (in shares) Common stock, ending balance (in shares) Common Stock, Shares, Issued Measure: Measure [Axis] Margin sharing Margin Sharing [Member] Margin Sharing Environmental obligations Accrued Environmental Loss Contingencies, Noncurrent Asset retirement obligations Asset Retirement Obligations, Noncurrent Cost of removal, net Payments for (Proceeds from) Removal Costs Equity Components [Axis] Equity Components [Axis] Product and Service [Domain] Product and Service [Domain] Class of Stock [Line Items] Class of Stock [Line Items] Income taxes paid, net Income Tax Paid, after Refund Received Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Entity Interactive Data Current Entity Interactive Data Current Deferred income taxes Deferred Income Tax Liabilities, Net Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Covid-19 deferred costs Covid 19 Deferred Costs [Member] Covid 19 Deferred Costs Reclassification adjustment for loss on available-for-sale investments included in net income, net of tax of $1 and $1 for the three months ended and $2 and $1 for the six months ended in 2026 and 2025, respectively Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax Entity Small Business Entity Small Business Comprehensive income attributable to common stockholders Comprehensive Income (Loss), Net of Tax, Attributable to Parent Amortization of postretirement liability losses included in net periodic benefit credit, tax Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax Termination Date Trading Arrangement Termination Date Discontinued operations Discontinued Operations, Policy [Policy Text Block] Utility Plant [Domain] Utility Plant [Domain] Discontinued operations, net of tax Income (loss) from discontinued operations, net of tax Discontinued operations, net of tax Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent Discontinued operations Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] 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 accrued liabilities Other Liabilities, Current Other Other Assets, Noncurrent Document Type Document Type Percentage investment in common stock of mid-cap companies Percentage Investment In Common Stock Of Mid-Cap Companies The percentage of insurance contracts in common stock of mid-cap companies. Fair Value as of Grant Date Award Grant Date Fair Value Operating Activities [Axis] Operating Activities [Axis] Net periodic benefit credit, including amount capitalized Defined Benefit Plan Net Periodic Benefit Cost Including Amount Capitalized The total amount of net periodic benefit cost including amount capitalized for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain or loss, prior service cost or credit, transition asset or obligation, and gain or loss due to settlements or curtailments), including amount capitalized. 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] Issuance of long-term debt Proceeds from Issuance of Long-Term Debt Local Phone Number Local Phone Number Other 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 Year One Year One [Member] Year One Environmental compliance programs Environmental Compliance Programs [Member] Environmental Compliance Programs Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Commitments and contingencies Commitments and Contingencies Operating revenues  Total external operating revenues External operating revenues Revenues Property, plant and equipment Property, Plant, and Equipment, before Accumulated Depreciation, Depletion, and Amortization Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Conservation programs Renewable Energy Program [Member] Executive Category: Executive Category [Axis] Receivable Type [Axis] Receivable Type [Axis] Percentage investment in common stock of large-cap companies Percentage Investment In Common Stock Of Large-Cap Companies The percentage of insurance contracts in common stock of large-cap companies. Liabilities and Stockholders' Equity Liabilities and Equity [Abstract] 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 Inventory, Net All Award Types 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] Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Supplemental cash flow information: Supplemental Cash Flow Information [Abstract] Purchased natural gas sold Utilities Operating Expense, Gas and Petroleum Purchased Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] PEO Name PEO Name Income (loss) from discontinued operations before income taxes Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Entity Tax Identification Number Entity Tax Identification Number Legal Entity [Axis] Legal Entity [Axis] Accounts Receivable, Allowance for Credit Loss [Roll Forward] Accounts Receivable, Allowance for Credit Loss [Roll Forward] Total debt to total capitalization Total Debt To Total Capitalization, Ratio Total Debt To Total Capitalization, Ratio Decoupling mechanisms Decoupling Mechanisms [Member] Decoupling Mechanisms Revenue from contracts with customers Revenue [Policy Text Block] Cash, cash equivalents and restricted cash - beginning of year Cash, cash equivalents and restricted cash - end of period Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Accounts payable Increase (Decrease) in Accounts Payable Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code 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] Basis of presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Debt Instrument [Axis] Debt Instrument [Axis] Employee stock-based compensation costs Share-Based Payment Arrangement, Noncash Expense Public Utilities, Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] Expected credit loss Credit Loss, Financial Instrument [Policy Text Block] Disposal Group Name [Axis] Disposal Group Name [Axis] Operating (loss) income Disposal Group, Including Discontinued Operation, Operating Income (Loss) Customer [Domain] Customer [Domain] Schedule of Inventories Schedule of Inventory, Current [Table Text Block] Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Earnings per share - basic (in usd per share) Earnings Per Share, Basic Mortgage-backed securities Collateralized Mortgage-Backed Securities [Member] Total current assets Assets, Current Statistical Measurement [Axis] Statistical Measurement [Axis] Insider Trading Arrangements [Line Items] Insurance contracts Insurance Contracts [Member] Insurance Contracts Long-term debt Net long-term debt Long-Term Debt, Excluding Current Maturities Award Type Award Type [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Industrial utility sales Industrial Utility Sales [Member] Industrial Utility Sales [Member] Retained earnings Retained Earnings (Accumulated Deficit) Product and Service [Axis] Product and Service [Axis] 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 [Member] Common Stock Common Stock [Member] Fair Value Available-for-sale securities: Debt Securities, Available-for-Sale Fair Value Measurement [Domain] Fair Value Measurement [Domain] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Cover [Abstract] Cover [Abstract] Stock-based compensation APIC, Share-Based Payment Arrangement, Recognition and Exercise Term Loan Agreements Loans Payable [Member] Equity Awards Adjustments Equity Awards Adjustments [Member] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Total liabilities and stockholders' equity  Liabilities and Equity Regulatory Asset [Domain] Regulatory Asset [Domain] Employee Stock Option Share-Based Payment Arrangement, Option [Member] Fair value, balance sheet grouping [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Discontinued operations, net of tax (in usd per share) Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share Supplemental employee retirement plans Supplemental Employee Retirement Plan [Member] Investments used to satisfy nonqualified benefit plans obligations Life Insurance, Corporate or Bank Owned, Amount Segments [Axis] Segments [Axis] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Notes issued Proceeds from Issuance of Senior Long-Term Debt Electric fuel and purchased power deferral Electric Fuel And Purchased Power Deferral [Member] Electric Fuel And Purchased Power Deferral Geographic Distribution [Domain] Geographic Distribution [Domain] Inventory Disclosure [Abstract] Inventory Disclosure [Abstract] Tabular List, Table Tabular List [Table Text Block] Montana-Dakota Utilities Co. Montana-Dakota Utilities Co. [Member] Montana-Dakota Utilities Co. [Member], a direct wholly owned subsidiary of MDU Energy Capital Other Notes Notes Payable to Banks [Member] Provision for rate refund Reserve For Refund [Member] Reserve For Refund Other income Other Nonoperating Income (Expense) Name Awards Close in Time to MNPI Disclosures, Individual Name Purchase of investment securities Payments to Acquire Investments 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] Regulatory assets: Regulatory Asset [Abstract] Electric Electric Distribution [Member] Noncurrent assets: Assets, Noncurrent [Abstract] Other utility sales Other Utility Sales [Member] Other utility sales Price per share (in dollars per share) Sale of Stock, Price Per Share Total regulatory liabilities Regulatory Liability Receivables, net Receivables, Net, Current Adjustment to Compensation: Adjustment to Compensation [Axis] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Interest, net Interest Paid, Excluding Capitalized Interest, Operating Activity Capital expenditures Payments to Acquire Productive Assets Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Pension and postretirement benefit plan contributions Payment for Pension and Other Postretirement Benefits Trade Accounts Receivable Trade Accounts Receivable [Member] Credit Facility [Axis] Credit Facility [Axis] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Total assets measured at fair value Assets, Fair Value Disclosure Investments Investment, Policy [Policy Text Block] Regulatory matters Schedule of Regulatory Assets and Liabilities [Text Block] Percentage investment in common stock of small-cap companies Percentage Investment In Common Stock Of Small-Cap Companies The percentage of insurance contracts in common stock of small-cap companies. Discontinued Operations and Disposal Groups [Abstract] Name Measure Name Accounts payable Accounts Payable, Current Pay vs Performance Disclosure [Line Items] Fair value, measurements [Domain] Fair Value Hierarchy and NAV [Domain] Everus Everus [Member] Everus Long-term debt outstanding [Line Items] Debt Instrument [Line Items] Other current assets Increase (Decrease) in Other Current Assets Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Other Corporate Segment and Other Operating Segment [Member] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Other Paid-in Capital Additional Paid-in Capital [Member] Entity Filer Category Entity Filer Category Rate Year [Axis] Rate Year [Axis] Rate Year Other Other Regulatory Assets (Liabilities) [Member] Other revenues Revenue Not from Contract with Customer Name Trading Arrangement, Individual Name Schedule of Regulatory Assets Schedule of Regulatory Assets [Table Text Block] Regulatory liabilities: Regulatory Liability [Abstract] Plant removal and decommissioning costs Removal Costs [Member] Cash, cash equivalents and restricted cash Cash and Cash Equivalent Annual Revenue Increase (%), pending Public Utilities, Requested Rate Increase (Decrease), Percentage Net regulatory position Net Regulatory Assets Company Selected Measure Amount Company Selected Measure Amount Depreciation and amortization Depreciation, Depletion and Amortization Entity Address, Address Line Two Entity Address, Address Line Two Stock, Class of Stock [Table] Stock, Class of Stock [Table] Investment withdrawal, cash amount Life Insurance, Corporate or Bank Owned, Change in Value Current assets: Assets, Current [Abstract] 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 assets obtained in exchange for new operating lease liabilities Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Income taxes Income tax (benefit) expense Income Tax Expense (Benefit) Award Timing Method Award Timing Method [Text Block] Forecast Forecast [Member] Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Loss contingency accrued Loss Contingency, Accrual, Current Pension and postretirement benefit plan net periodic benefit cost (credit) Pension and Other Postretirement Benefits Expense (Reversal of Expense), Noncash Amortization of net actuarial gain Defined Benefit Plan, Amortization of Gain (Loss) New accounting standards Accounting Standards Update and Change in Accounting Principle [Text Block] Net income 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] Cost recovery mechanisms Regulatory Clause Revenues, over-Recovered [Member] Rate action of a regulator resulting in capitalization or accrual of over-recovered regulatory clause revenue. ROE, approved Public Utilities, Approved Return on Equity, Percentage Restatement Determination Date: Restatement Determination Date [Axis] Regulatory liabilities due within one year Regulatory Liability, Current Schedule of Remaining Performance Obligations Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block] Commercial utility sales Commercial Utility Sales [Member] Commercial utility sales [Member] Receivables Increase (Decrease) in Receivables Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings Adjustments To Additional Paid In Capital, Stock Issued During Period, Value, Treasury Stock Reissued Through Share-Based Payment Arrangement Adjustments To Additional Paid In Capital, Stock Issued During Period, Value, Treasury Stock Reissued Through Share-Based Payment Arrangement Income from continuing operations Income from continuing operations Income (loss) from continuing operations Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Firm Transportation Contract Firm Transportation Contract [Member] Firm Transportation Contract AFUDC borrowed Capitalized Interest Costs, Including Allowance for Funds Used During Construction Natural gas in storage (current) Energy Related Inventory, Natural Gas in Storage Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Geographic Distribution [Axis] Geographic Distribution [Axis] Long-term debt refinancing costs Loss on Reacquired Debt [Member] Loss contingency, complaint Loss Contingency, Damages Sought, Value Credit loss recoveries collected Accounts Receivable, Allowance for Credit Loss, Recovery Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block]