Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Trading Arrangement: Trading Arrangement [Axis] Current receivables Contract with Customer, Asset, before Allowance for Credit Loss, Current Maximum Maximum [Member] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Range [Domain] Statistical Measurement [Domain] Less: Accumulated provision for depreciation Public Utilities, Property, Plant and Equipment, Accumulated Depreciation Short-Term Debt, Type [Axis] Short-Term Debt, Type [Axis] Subsequent Event Subsequent Event [Member] Carrying Value Reported Value Measurement [Member] Document Fiscal Year Focus Document Fiscal Year Focus Assets Derivative Liability, Subject to Master Netting Arrangement, Asset Offset Net derivative assets (liabilities) Net Carrying Value Presented on the Balance Sheet Derivative Assets (Liabilities), at Fair Value, Net Adjustment to Compensation, Amount Adjustment to Compensation Amount Financial Instrument [Axis] Financial Instrument [Axis] Number of operating leases Number Of Operating Leases Number Of Operating Leases Segment Reporting [Abstract] Segment Reporting [Abstract] Customer [Axis] Customer [Axis] 2027 Lessee, Operating Lease, Liability, to be Paid, Year One Public Utilities, General Disclosures [Line Items] Public Utilities, General Disclosures [Line Items] FFB Debt From Federal Financing Bank [Member] Represents details pertaining to debt from the Federal Financing Bank. Leases Lessee, Finance Leases [Text Block] Increase (decrease) in commercial paper borrowings, net Proceeds from (Repayments of) Commercial Paper Line of Credit Line of Credit [Member] Restatement Determination Date Restatement Determination Date 2027 Finance Lease, Liability, to be Paid, Year One Derivative Instrument [Axis] Derivative Instrument [Axis] Regulatory liabilities Total Regulatory Liabilities Regulatory Liability, Noncurrent Activity in nuclear decommissioning trust fund—Proceeds Proceeds from Decommissioning Trust Fund Assets Amendment Flag Amendment Flag Current liabilities: Liabilities, Current [Abstract] Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Financing cash flows from finance leases Finance Lease, Principal Payments Allowance for equity funds used during construction Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity Rural Utilities Service Guaranteed Loans Debt From Federal Financing Bank Rural Utilities Service Guaranteed Loans [Member] Represents details pertaining to Rural utilities service guaranteed loans from the Federal Financing Bank. Rate management program, billing period Rate Management Program, Billing Period Rate Management Program, Billing Period Right-of-use assets—finance leases Right-of-use assets Finance Lease, Right-of-Use Asset, before Accumulated Amortization Weighted-average remaining lease term (in years) Weighted-Average Remaining Lease Term [Abstract] n/a Cost Debt Securities, Trading, and Equity Securities, FV-NI, Cost [Abstract] Leases [Abstract] Leases [Abstract] Deferral of effects on net margin Deferred Effects On Net Margin For Energy Facilities [Member] Discloses the amount of regulatory liabilities related to the effects on net margin for energy facilities that is deferred. Total deferred credits and other liabilities Liabilities, Noncurrent Amortization period, other regulatory assets Regulatory Asset, Amortization Period Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Schedule of Notional Volume of Natural Gas Derivatives that is Expected to Settle or Mature Each Year Schedule of Price Risk Derivatives [Table Text Block] Accumulated retirement costs for other obligations Accumulated Retirement Costs Other Obligation [Member] Represents portion of the carrying amount of a liability for future retirement costs associated with long-lived assets for which there is no legal obligation to retire. This deferred liability is not expected to reduce revenues required from Members within one year or the normal operating cycle if longer. Entity Address, State or Province Entity Address, State or Province Smarr Combined Cycle Project Talbot Combustion Turbine Unit No. 7 Public Utilities Disclosure [Text Block] Amortization of deferred gains Amortization of Deferred Hedge Gains PEO Total Compensation Amount PEO Total Compensation Amount Deferred outage costs Deferred Outage Costs Costs of repairs and maintenance incurred in the current period that is expected to be recovered from customers in future periods. Asset Acquisition [Axis] Asset Acquisition [Axis] Liabilities Derivative Liability, Subject to Master Netting Arrangement, before Offset of Collateral [Abstract] Deferred credits and other liabilities: Liabilities, Noncurrent [Abstract] Total investments and funds 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 Capitalization, Long-Term Debt and Equity Regulatory assets Total Regulatory Assets Regulatory Asset, Noncurrent Number of reportable segments Number of Reportable Segments Total current liabilities Liabilities, Current 2030 Lessee, Operating Lease, Liability, to be Paid, Year Four Regulatory Liability [Axis] Regulatory Liability [Axis] Other Other Securities [Member] Represents the information pertaining to investments in other securities. Domestic equity Domestic Equity [Member] Represents the information pertaining to investments in equity that are issued by domestic companies. Allowance for debt funds used during construction Allowance For Debt Funds Used During Construction Amount of allowance for debt funds used during construction. Short-Term Debt, Type [Domain] Short-Term Debt, Type [Domain] Lease Cost Lease, Cost [Abstract] Short-term investments: Treasury STRIPS Treasury Separate Trading Of Registered Interest And Principal Of Securities, Short-Term [Member] Treasury Separate Trading Of Registered Interest And Principal Of Securities, Short-Term Entity Address, City or Town Entity Address, City or Town 2029 Lessee, Finance Lease And Operating Lease, Liability, To Be Paid, Due Year Three Amount of lessee's undiscounted obligation for lease payments for finance lease and operating lease, due in third fiscal year following latest fiscal year. Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Non-US Gov't bonds & private placements Non Us Government Bonds And Private Placement [Member] Represents information pertaining to non-US government bonds and private placement. Washington and Baconton Acquisition Washington and Baconton Acquisition [Member] Washington and Baconton Acquisition Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount CFC Term Loan CFC Term Loan [Member] CFC Term Loan Receivable [Domain] Receivable [Domain] (Level 2) Fair Value, Inputs, Level 2 [Member] Other income: Nonoperating Income (Expense) [Abstract] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Maximum borrowing capacity designated for capitalized interest Line of Credit Facility, Maximum Borrowing Capacity Designated For Capitalized Interest Maximum borrowing capacity under the credit facility designated for capitalized interest. Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Amortization period, regulatory liability Regulatory Liability, Amortization Period Recently Issued or Adopted Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Accrued property additions at end of period Capital Expenditures Incurred but Not yet Paid Rate management program billing credits applied Increase (Decrease) in Contract with Customer, Liability Municipal bonds Municipal Bonds [Member] Aggregate borrowings including capitalized interest Long-Term Debt Schedule of Maturities of Operating Lease Liabilities Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block] Supplemental disclosure of non-cash investing and financing activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Amounts billed under additional rate management program Rate Management Program, Billing Amount The amount of billing made by participating members under rate management program. Document Period End Date Document Period End Date Change in operating assets and liabilities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Asset retirement obligations Asset Retirement Obligation Costs [Member] Number of renewal options Lessee, Operating Lease, Number Of Renewal Options Lessee, Operating Lease, Number Of Renewal Options Deferred debt service adder Deferred Debt Service Adder [Member] Discloses the amount of regulatory liabilities related to the collections to fund debt payments in excess of depreciation expense. Net cash used in investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Nuclear fuel, at amortized cost Nuclear Fuel, Net of Amortization Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Total Debt Securities, Trading, and Equity Securities, FV-NI, Cost Debt instrument, face amount Debt Instrument, Face Amount 2028 Lessee, Operating Lease, Liability, to be Paid, Year Two Other Information: Lessee Disclosure [Abstract] Leases Lessor, Operating Leases [Text Block] Federal agency securities Agency Securities [Member] Number of combined units of cycle generation facility Public Utilities, Development And Construction Of Generation Facility, Number Of Units Public Utilities, Development And Construction Of Generation Facility, Number Of Units Finance leases Finance Lease, Weighted Average Remaining Lease Term Activity in long-term and short-term investments—Purchases Payments to Acquire Marketable Securities Entity Shell Company Entity Shell Company Other current liabilities Operating Lease, Liability, Current Long-term receivables Contract with Customer, Asset, before Allowance for Credit Loss, Noncurrent Unrealized loss position, 12 months or longer Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer Depreciation and amortization, including nuclear fuel Depreciation, Depletion and Amortization Excluding Accretion and Amortization Of Deferred Gains The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets, excluding accretion cost and amortization of deferred gains. Accrued interest Interest Payable, Current Total finance lease assets Finance Lease, Right-of-Use Asset, after Accumulated Amortization Name Outstanding Recovery, Individual Name Activity in long-term and short-term investments—Proceeds Proceeds from Sale and Maturity of Marketable Securities 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] Department of Energy Guarantee Financial Guarantee [Member] Total Debt Securities, Trading, and Equity Securities, FV-NI Cash paid for amounts included in the measurement of lease liabilities Cash Flow, Lessee [Abstract] Cash Flow, Lessee Deferred charges and other assets: Deferred Costs [Abstract] Accrued taxes Increase (Decrease) in Property and Other Taxes Payable Depreciation and amortization Utilities Operating Expense, Depreciation and Amortization Jointly Owned Utility Plant Name [Domain] Jointly Owned Utility Plant Name [Domain] Name of the jointly owned utility plant. 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] Purchased power Utilities Operating Expense, Purchased Power Total operating expenses Utilities Operating Expense Company Selected Measure Name Company Selected Measure Name Plant Wansley Plant Wansley [Member] Plant Wansley Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash Restrictions on Cash and Cash Equivalents [Table Text Block] Amortization of debt discount and expense Amortization of Debt Issuance Costs and Discounts Reclassification, Type [Axis] Reclassification, Type [Axis] Net unrealized gains on derivative instruments Unrealized Gain (Loss) on Derivatives Other Other Long-Term Investments Other regulatory assets Other Regulatory Assets [Member] Represents the amount related to other certain costs that are probable of recovery from members in future revenues through rates. Thereafter Lessee, Finance Lease And Operating Lease, Liability, To Be Paid, Due after Year Four Lessee, Finance Lease And Operating Lease, Liability, To Be Paid, Due after Year Four Schedule of Debt and Equity Securities Debt Securities, Trading, and Equity Securities, FV-NI [Table Text Block] Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). TA Smith Energy Facility TA Smith Energy Facility [Member] TA Smith Energy Facility Equity Equity Securities, FV-NI, Cost Credit Facility [Domain] Credit Facility [Domain] Cash flows from operating activities: Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Gross Unrealized Losses Debt and Equity Securities, Unrealized Loss [Abstract] n/a Compensation Amount Outstanding Recovery Compensation Amount Individual: Individual [Axis] Public Utility [Axis] Public Utility [Axis] Revenue Recognition Disaggregation of Revenue [Line Items] Measurement of Credit Losses on Financial Instruments Allowance for Credit Losses [Text Block] Entity Emerging Growth Company Entity Emerging Growth Company Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] BC Smith Energy Facility BC Smith Energy Facility [Member] BC Smith Energy Facility 2028 Finance Lease, Liability, to be Paid, Year Two Underlying Security Market Price Change Underlying Security Market Price Change, Percent 2030 Finance Lease, Liability, to be Paid, Year Four Commercial Paper Commercial Paper [Member] Derivative Instruments Derivative Instruments and Hedging Activities Disclosure [Text Block] US Treasury securities US Treasury Securities [Member] Litigation proceeds received for capitalized spent nuclear fuel storage costs Proceeds From Nuclear Fuel Costs Recovery Proceeds From Nuclear Fuel Costs Litigation Recovery Other Other Securities, FV-NI, Unrealized Loss Other Securities, FV-NI, Unrealized Loss Regulatory Asset [Axis] Regulatory Asset [Axis] Deferral of direct pay nuclear production tax credits Deferral Nuclear Production Tax [Member] Deferral Nuclear Production Tax Less: imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Deferred charges related to Vogtle Units No. 3 and No. 4 training costs Jointly Owned Utility Plant, Deferred Charges Related To Vogtle Units No. 3 And No. 4 Training Costs [Member] Represents training and interest related carrying costs of such training associated with Vogtle Units No. 3 and No. 4 which are being deferred until commercial operation of each unit. Short-term borrowings Short-Term Debt Prepayments to Georgia Power Company Prepaid Expense Liabilities Derivative Liability, Subject to Master Netting Arrangement, before Offset Total deferred charges Assets, Noncurrent, Other than Noncurrent Investments and Property, Plant and Equipment Available borrowing capacity Line of Credit Facility, Current Borrowing Capacity Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Less: imputed interest Finance Lease, Liability, Undiscounted Excess Amount Ashpond and other Ashpond And Other [Member] Represents information pertaining to Ashpond and other. 2030 Lessee, Finance Lease And Operating Lease, Liability, To Be Paid, Due Year Four Amount of lessee's undiscounted obligation for lease payments for finance lease and operating lease, due in fourth fiscal year following latest fiscal year. Lease Term and Discount Rate: Disclosure of Lease Quantitative Information [Abstract] No definition available. Sales to members Cooperative Members [Member] Represents information pertaining to cooperative members. Plant Vogtle Plant Vogtle [Member] Represents information pertaining to Plant Vogtle, a jointly owned utility plant. Operating cash flows from operating leases Operating Lease, Payments Other Other Securities, FV-NI, Unrealized Gain Amount of unrealized gain on investment in other securities measured at fair value with change in fair value recognized in net income (FV-NI). Award Timing Predetermined Award Timing Predetermined [Flag] Total electric plant Public Utilities, Property, Plant and Equipment, Net Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] 2027 Lessee, Finance Lease And Operating Lease, Liability, To Be Paid, Due Next Twelve Months Lessee, Finance Lease And Operating Lease, Liability, To Be Paid, Due Next Twelve Months (Level 1) Fair Value, Inputs, Level 1 [Member] Thereafter Lessee, Operating Lease, Liability, To Be Paid, Due after Year Four Lessee, Operating Lease, Liability, To Be Paid, Due after Year Four Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Loss (gain) on sale of investments Gain (Loss) on Sale of Investments Total lease payments Lessee, Operating Lease, Liability, to be Paid Member Capital Components [Axis] Member Capital Components [Axis] Components of members' equity are the parts of the total equity balance including that which is allocated to members' capital and accumulated other comprehensive income, etc. Schedule of Lease Terms and Discount Rates Lessee, Quantitative Disclosure for Leases [Table Text Block] Tabular disclosure of quantitative information about lessee's operating and capital leases. All Executive Categories All Executive Categories [Member] Regulated Operations [Abstract] Finance leases Finance leases N/A Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Long-term debt Long-Term Debt, Fair Value International mutual funds International Mutual Fund [Member] International Mutual Fund Net interest charges Interest and Debt Expense Asset Acquisition [Domain] Asset Acquisition [Domain] Scenario [Domain] Scenario [Domain] Liabilities Derivative, Subject To Master Netting Arrangement, Before Offset, Net Derivative, Subject To Master Netting Arrangement, Before Offset, Net Total operating lease assets Operating Lease, Right-of-Use Asset Lease liabilities—Operating leases Operating Lease, Liability [Abstract] Lease liabilities—Finance leases Finance Lease, Liability [Abstract] Activity in nuclear decommissioning trust fund—Purchases Payments to Acquire Investments to be Held in Decommissioning Trust Fund Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Axis] Regulatory Assets and Liabilities Regulatory Assets and Liabilities [Line Items] Operating lease, renewal term Lessee, Operating Lease, Renewal Term Debt Debt Securities, Trading, Amortized Cost Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Debt Disclosure [Abstract] Debt Disclosure [Abstract] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Long-term debt and finance leases due within one year Long-Term Debt and Lease Obligation, Current Outage costs Unamortized Deferred Outage Costs Net [Member] Coal-fire outage and nuclear refueling outage costs, accounted for as regulatory assets, are deferred and amortized on a straight-line basis to expense over an 18 to 36-month period. Reportable Segment Information Segment Reporting [Text Block] Investment Securities Investment in Debt and Equity Securities and Other Trading Assets [Text Block] Line of credit, amount outstanding Long-Term Line of Credit Reclassification, Type [Domain] Reclassification, Type [Domain] Minimum Minimum [Member] Other Other Securities, FV-NI Amount of investment in other securities measured at fair value with change in fair value recognized in net income (FV-NI). Expiration Date Trading Arrangement Expiration Date Long-term investments Investments, Fair Value Disclosure Lease Arrangements [Axis] Lease Arrangements [Axis] Lease Arrangements Schedule of Sales to Members and Sales to Non-Members Disaggregation of Revenue [Table Text Block] Restricted cash included in restricted cash and short-term investments Restricted Cash and Cash Equivalent Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Revenue deferral plan Revenue Deferral Plan [Member] Representing information pertaining to revenue deferral plan. 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] Inventory adjustments Inventory Adjustments [Member] Inventory Adjustments Less: imputed interest Lessee, Finance Lease And Operating Lease, Liability, Undiscounted Excess Amount Amount of lessee's undiscounted obligation for lease payments in excess of discounted obligation for lease payments for operating lease. Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Derivative [Table] Derivative [Table] Finance lease renewal term Lessee, Finance Lease, Renewal Term Asset Retirement Obligation Disclosure [Abstract] Schedule of Estimated Fair Values of Long-term Debt, Including Current Maturities Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block] Exercise Price Award Exercise Price Cash flows from investing activities: Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Document Quarterly Report Document Quarterly Report 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] Lease Disclosure [Table] Lease Disclosure [Table] Disclosure of information about leases. Debt Debt Disclosure [Text Block] Scenario [Axis] Scenario [Axis] Long-term debt payments Repayments of long-term debt Repayments of Long-Term Debt Regulatory Assets and Liabilities Disclosure [Abstract] Regulatory Assets and Liabilities Disclosure [Abstract] Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Lease Contractual Term [Axis] Lease Contractual Term [Axis] Investment in associated companies Equity Method Investments Present value of lease liabilities Finance Lease And Operating Lease, Liability Present value of lessee's discounted obligation for lease payments from finance lease and operating lease. PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Secured Debt Secured Debt [Member] Business Combination, Asset Acquisition, Transaction between Entities under Common Control, and Joint Venture Formation [Abstract] Refund liability Contract with Customer, Refund Liability Adoption Date Trading Arrangement Adoption Date Finance leases Finance Lease, Weighted Average Discount Rate, Percent 2029 Settlement Or Maturity Period, Year Three [Member] Represents the derivative contracts that are expected to settle or mature in 2022. Total other income Nonoperating Income (Expense) Major maintenance reserve Major Maintenance Sinking Fund [Member] Represents collections for future major maintenance costs that will offset by deferred revenues when incurred. Equity Equity Securities, FV-NI, Current 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 Accounting Policies [Abstract] Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Total operating lease liabilities Present value of lease liabilities Operating Lease, Liability Insider Trading Policies and Procedures [Line Items] Total finance lease liabilities Present value of lease liabilities Finance Lease, Liability Capacity revenues Capacity Services [Member] Represents the revenue from capacity services. Other Proceeds from (Payment for) Other Financing Activity Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Prepayments and other current assets Prepaid Expense and Other Assets, Current Derivative Instruments Derivative Instruments, Gain (Loss) [Line Items] Derivative Settlement or Maturity by Period [Axis] Derivative Settlement or Maturity by Period [Axis] Information pertaining to the settlement or maturity period of derivative contracts. Letter of Credit Letter of Credit [Member] 2031 Settlement Or Maturity Period, Year Five [Member] Settlement Or Maturity Period, Year Five Spent Nuclear Fuel Storage Costs Commitments and Contingencies Disclosure [Text Block] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Lease income Operating Lease, Lease Income Number of operating segments Number of Operating Segments Entity Central Index Key Entity Central Index Key Operating leases Operating leases N/A All Adjustments to Compensation All Adjustments to Compensation [Member] Other Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Other Item 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 Settlement of asset retirement obligations Asset Retirement Obligation, Cash Paid to Settle Contingencies and Regulatory Matters Legal Matters and Contingencies [Text Block] Income Statement [Abstract] Income Statement [Abstract] Document Transition Report Document Transition Report Minimum margins to interest ratio Minimum Margins to Interest Ratio Represents the minimum margins to interest ratio required to be maintained under first mortgage indenture by the entity. Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Operating expenses: Operating Expenses [Abstract] Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Obligation under finance leases Obligations under finance leases Finance Lease, Liability, Noncurrent Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] City Area Code City Area Code Total lease payments Finance Lease, Liability, to be Paid All Individuals All Individuals [Member] Name Forgone Recovery, Individual Name Schedule of Lease and Non-lease Components for all Lease Agreements Lessee, Balance Sheet Disclosures [Table Text Block] Tabular disclosure of balance sheet impact for lessee's operating and finance leases. Reclassification, Other Reclassification, Other [Member] Regulatory Liability [Domain] Regulatory Liability [Domain] Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Nuclear refueling outage costs Unamortized Deferred Nuclear Refueling Outage Costs Net [Member] Nuclear refueling outage costs, accounted for as regulatory assets, are deferred and amortized on a straight-line basis to expense over an 18 to 24-month period. Statement [Line Items] Statement [Line Items] Statement [Line Items] Long-term investments Marketable Securities, Noncurrent Lease Terms Through December 31, 2027 Finance Lease Agreements With Terms Through December 31 2027 [Member] Represents information pertaining to finance lease agreements with terms through December 31, 2027. Total assets Assets Amortized cost basis, unrealized loss positions Debt Securities, Available-for-Sale, Amortized Cost, Unrealized Loss Positions Debt Securities, Available-for-Sale, Amortized Cost, Unrealized Loss Positions Operating Leases Lessee, Operating Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract] Notional volume of natural gas derivatives (in MMBTUs) Derivative, Nonmonetary Notional Amount, Energy Measure New Accounting Pronouncements and Changes in Accounting Principles [Abstract] Accounting Standards Update and Change in Accounting Principle [Abstract] Less: Accumulated provision for depreciation Finance Lease, Right-of-Use Asset, Accumulated Amortization Development and construction of generation facility, generating capacity (in megawatts) Public Utilities, Development And Construction Of Generation Facility, Generating Capacity, Megawatts Public Utilities, Development And Construction Of Generation Facility, Generating Capacity, Megawatts Interest expense Interest Expense, Nonoperating Schedule of Unrealized Gains on Derivative Instruments Deferred on the Balance Sheet Schedule of Derivatives Instruments Gain (Loss) in Statement of Financial Position [Table Text Block] Tabular disclosure of the location and amount of gains and losses reported in the statement of financial position related to derivative instruments. Assets Derivative, Subject to Master Netting Arrangement, Offset, Net Derivative, Subject to Master Netting Arrangement, Offset, Net PEO PEO [Member] Nuclear decommissioning trust fund Nuclear decommissioning trust funds Nuclear Decommissioning Trust Funds, Fair Value The fair value of investments held in a trust fund to pay for the costs of decontaminating and decommissioning facilities, including net realized gains (losses), interest income and dividends, and contributions and fees. Schedule of Debt Instruments [Table] Schedule of Debt Instruments [Table] A table or schedule providing information pertaining to short-term and long-term debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. Liabilities Derivative Asset, Subject to Master Netting Arrangement, Liability Offset Measurement Basis [Axis] Measurement Basis [Axis] Other Other Liabilities, Noncurrent Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Operating license expected extension period for Plant Vogtle Operating License, Expected Extension Period Represents the expected extension period of the plant operating license. Taxable Municipal Bonds Taxable Municipal Bonds [Member] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Capitalization—Other Operating Lease, Liability, Noncurrent Lease Terms Through June 30, 2031 Finance Lease Agreements With Terms Through June 30 2031 [Member] Represents information pertaining to finance lease agreements with terms through June 30, 2031. Asset Retirement Obligations Asset Retirement Obligation Disclosure [Text Block] Jointly Owned Utility Plant Name [Axis] Jointly Owned Utility Plant Name [Axis] Information by the name of the jointly owned utility plant. Number of finance leases Number Of Finance Leases The number of finance leases. Investment income Investment Income Net and Gain (Loss) This item represents investment income derived from investments in debt and equity securities consisting of interest income earned from investments in debt securities and on cash and cash equivalents, dividend income from investments in equity securities, and income or expense derived from the amortization of investment related discounts or premiums, respectively, net of related investment expenses. It also includes the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain or loss of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain or loss which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains or losses realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments of the subject investments. Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Award Timing Disclosures [Line Items] Patronage Capital and Membership Fees Patronage Capital And Membership Fees [Member] This element represents the patronage capital and membership fees. Entity Current Reporting Status Entity Current Reporting Status Net cash provided by financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Total Shareholder Return Amount Total Shareholder Return Amount Cost incurred for combined cycle project Public Utilities, Development And Construction Of Generation Facility, Costs Incurred Public Utilities, Development And Construction Of Generation Facility, Costs Incurred Prepayments and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Member Power Bill Prepayments Member Power Bill Prepayments Disclosure [Text Block] This element represents the entire disclosure related to the power bill prepayment program. With this program, members can prepay their power bills from the entity at a discount based on avoided cost of borrowing during the period. Schedule of Debt Instruments [Line Items] Schedule of Debt Instruments [Line Items] Schedule of Debt Instruments [Line Items] Fair Value Debt Securities, Trading, and Equity Securities, FV-NI [Abstract] Debt Debt Securities, Trading, Unrealized Gain Lease Contractual Term [Domain] Lease Contractual Term [Domain] Adjustments to reconcile net margin to net cash provided by operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Weighted-average discount rate: Weighted-Average Discount Rate [Abstract] n/a Total Debt Securities, Trading, and Equity Securities, Unrealized Gain Amount of unrealized gain on investment in debt and equity securities measured at fair value with change in fair value recognized in net income. Cash flows from financing activities: Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Total operating revenues Revenue from Contract with Customer, Excluding Assessed Tax Financial Instruments [Domain] Financial Instruments [Domain] Derivative asset Net Carrying Value Presented on the Balance Sheet Derivative Asset Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Underlying Securities Award Underlying Securities Amount Beginning balance Ending balance Patronage Capital and Membership Fees Equity, Net Sum of retained net margin, cooperative membership fees and accumulated other comprehensive income or loss, net of tax. Operating license period Operating License Period Represents the period of the plant operating license. Fair Value Estimate of Fair Value Measurement [Member] Revenue Recognition Revenue from Contract with Customer [Text Block] Credit Agreement Credit Agreement [Member] Credit Agreement Right-of-use assets—Operating leases Operating Lease, Right-of-Use Asset [Abstract] n/a Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Sales to non-members Non Members [Member] Represents information pertaining to customers who are not members. Accrued interest Increase (Decrease) in Interest Payable, Net Leases Lease Disclosure [Line Items] Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Maturity analysis of finance and operating lease liabilities Maturity Analysis of Finance and Operating Lease Liabilities [Abstract] n/a Other Payment for (Proceeds from) Other Investing Activity Inventories Increase (Decrease) in Inventories Operating leases Operating Lease, Weighted Average Discount Rate, Percent Percentage of undivided interest in Scherer Unit No. 2 Percentage Of Undivided Interest, Property, Plant and Equipment The percentage of undivided interest in property, plant and equipment. Other Other Capitalization Obligations, Noncurrent Other Capitalization Obligations, Noncurrent Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Schedule of Lease Cost Lease, Cost [Table Text Block] Natural gas swaps gains Derivative, Gain on Derivative Commitments and Contingencies Disclosure [Abstract] All Trading Arrangements All Trading Arrangements [Member] Unrealized loss position, less than 12 months Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months Total Derivative, Gain (Loss) on Derivative, Net Other Performance Measure, Amount Other Performance Measure, Amount Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Operating margin Operating Income (Loss) Cash paid for— Interest Paid, Including Capitalized Interest, Operating and Investing Activities [Abstract] Current Fiscal Year End Date Current Fiscal Year End Date Schedule of Maturities of Finance Lease Liabilities Finance Lease, Liability, to be Paid, Maturity [Table Text Block] 2026 Finance Lease, Liability, to be Paid, Remainder of Fiscal Year Advances received on loans Proceeds from issuance of debt Proceeds from Issuance of Debt Amortization of financing leases Amortization Of Financing Leases [Member] Represents the information pertaining to amortization of financing leases. Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Rate management program, amount expected to be collected Rate Management Program, Amount Expected To Be Collected Rate Management Program, Amount Expected To Be Collected Derivative Instruments Derivative [Line Items] Sale of Bobby C. Smith Jr. Deferring Members' Output Sale Of Bobby C. Smith Jr. Deferring Members' Output [Member] Sale Of Bobby C. Smith Jr. Deferring Members' Output Production Utilities Operating Expense, Products and Services 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] Deferral of effects on net margin Deferred Effect On Net Margin For Energy Facilities [Member] Disclosure of the amount of regulatory assets related to the effects on net margin for energy facilities that is deferred. Entity File Number Entity File Number Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Total lease payments Lessee, Finance Lease And Operating Lease, Liability, To Be Paid, Due Amount of lessee's undiscounted obligation for lease payments for finance lease and operating lease. Corporate bonds and debt Corporate Bond Securities [Member] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Lease Arrangements [Domain] Lease Arrangements [Domain] Lease Arrangements Measure: Measure [Axis] Electric plant in service, net Operating Lease, Right-of-Use Asset, Noncurrent Amount of lessee's right to use underlying asset under operating lease, classified as noncurrent. Debt Debt Securities, Trading, Unrealized Loss Equity Equity Securities, FV-NI, Unrealized Gain Total Debt Securities, Trading, and Equity Securities, Unrealized Loss Amount of unrealized loss on investment in debt and equity securities measured at fair value with change in fair value recognized in net income. Asset retirement obligations Asset Retirement Obligations, Noncurrent Total adjustments Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity 2030 Settlement Or Maturity Period, Year Four [Member] Represents the derivative contracts that are expected to settle or mature in 2023. Product and Service [Domain] Product and Service [Domain] Depreciation expense Unamortized Deferred Depreciation Expense [Member] Carrying amount as of the balance sheet date of capitalized costs related to the excess of plant depreciation expense based on the current operating license versus depreciation expense based on the applied for license extension, accounted for as a regulatory asset. These capitalized costs are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer. Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Capitalization: Capitalization [Abstract] Entity Interactive Data Current Entity Interactive Data Current Long-term debt and finance leases due within one year Finance Lease, Liability, Current Investments and funds: Investments and Funds [Abstract] Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Entity Small Business Entity Small Business In service Public Utilities, Property, Plant and Equipment, Plant in Service 2029 Lessee, Operating Lease, Liability, to be Paid, Year Three Termination Date Trading Arrangement Termination Date Utility Plant [Domain] Utility Plant [Domain] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Natural gas swaps losses Derivative, Loss on Derivative Assets Derivative Asset, Subject to Master Netting Arrangement, before Offset of Collateral [Abstract] 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 2029 Finance Lease, Liability, to be Paid, Year Three Document Type Document Type Fair value Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] 2028 Settlement Or Maturity Period, Year Two [Member] Represents the derivative contracts that are expected to settle or mature in 2021. Fair Value as of Grant Date Award Grant Date Fair Value Scherer Unit No. 2 Scherer Unit Number2 [Member] Represents information pertaining to Scherer Unit No. 2, a jointly owned utility plant under a capital lease. Other regulatory liabilities Other Regulatory Liabilities [Member] Represents the amount related to other certain items of income that are being retained and will be applied in the future to reduce revenues required to be recovered from members. Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Arrangement Duration Trading Arrangement Duration Long-term debt proceeds Proceeds from Issuance of Long-Term Debt Local Phone Number Local Phone Number Member power bill prepayments, non-current Contract with Customer, Liability, Noncurrent Combined Turbine Unit Facility in Talbot County, Georgia Combined Turbine Unit Facility in Talbot County, Georgia [Member] Combined Turbine Unit Facility in Talbot County, Georgia Treasury STRIPS Treasury Separate Trading Of Registered Interest And Principal Of Securities, Long-Term [Member] Treasury Separate Trading Of Registered Interest And Principal Of Securities, Long-Term Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Registrant Name Entity Registrant Name Obligation under Rocky Mountain transactions Obligation under Hydro Facility Transactions Carrying value as of the balance sheet date of the portion of the fixed purchase price to repurchase the Rocky Mountain facility that will be funded by equity funding agreements. Vogtle New Units Vogtle New Units [Member] Represents information pertaining to Vogtle New Units. Prepayment premium Payment for Debt Extinguishment or Debt Prepayment Cost Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Restricted cash and short-term investments Restricted Cash and Investments, Current 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 Executive Category: Executive Category [Axis] Margins for interest ratio Margins for Interest Ratio Represents the ratio of margins for interest to total interest charges for a given period. Amortization of leased assets Finance Lease, Right-of-Use Asset, Amortization Number of parties required to post collateral Number Of Parties Required To Post Collateral Number Of Parties Required To Post Collateral Receivable Type [Axis] Receivable Type [Axis] Contingencies and Regulatory Matters Contingencies and Regulatory Matters [Abstract] No definition available. Equity and Liabilities Liabilities and Equity [Abstract] Other revenue deferral plan Other Revenue Deferral Plan [Member] Other Revenue Deferral Plan Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] All Award Types Award Type [Domain] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Natural gas hedges Natural Gas Hedges [Member] Natural Gas Hedges Interest on lease liabilities Finance Lease, Interest Expense Receivable from U.S. Government, Nuclear Production Tax Credit Receivable from U.S. Government, Nuclear Production Tax Credit [Member] Receivable from U.S. Government, Nuclear Production Tax Credit 2026 Lessee, Operating Lease, Liability, to be Paid, Remainder of Fiscal Year Fair Value Fair Value Disclosures [Text Block] Thereafter Finance Lease, Liability, To Be Paid, Due after Year Four Finance Lease, Liability, To Be Paid, Due after Year Four (Level 3) Fair Value, Inputs, Level 3 [Member] Supplemental cash flow information: Supplemental Cash Flow Information [Abstract] PEO Name PEO Name Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Entity Tax Identification Number Entity Tax Identification Number Domestic mutual funds Mutual Fund [Member] 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 reported in the consolidated statements of cash flows 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] Inventories, at weighted average cost Public Utilities, Inventory 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] General Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Debt Instrument [Axis] Debt Instrument [Axis] Total leased cost Lease, Cost Number of services provided Number Of Services Provided Represents the number of services provided. Leases Lessee, Operating Leases [Text Block] Customer [Domain] Customer [Domain] Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Schedule of Fair Value of Derivative Instruments and Effect on Consolidated Balance Sheets Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Member power bill prepayments, current Contract with Customer, Liability, Current Mortgage backed securities Collateralized Mortgage-Backed Securities [Member] Total current assets Assets, Current Range [Axis] Statistical Measurement [Axis] Insider Trading Arrangements [Line Items] Schedule of the Realized Gains and (Losses) on Derivative Instruments Recognized in Margin Derivative Instruments, Gain (Loss) [Table Text Block] Long-term debt Long-Term Debt, Excluding Current Maturities Award Type Award Type [Axis] Lessor Lessor Disclosure [Abstract] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Natural gas swaps Natural Gas Swaps Commodity Contract [Member] 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] Number of separate facilities Line of Credit Facility Number of Facilities Represents the number of short-term credit facilities availed by the entity for general working capital purposes. Variable Rate Demand Obligation Variable Rate Demand Obligation [Member] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Total Lessee, Operating Lease and Finance Lease, Liability, Payment, Due [Abstract] n/a Fair Value Measurement [Domain] Fair Value Measurement [Domain] Schedule of Lease Income Operating Lease, Lease Income [Table Text Block] Fuel Utilities Operating Expense, Fuel Used Schedule of Cash Paid for Amounts Included in the Measurement of Lease Liabilities Lessee, Measurement Of Lease Liabilities [Table Text Block] Tabular disclosure of cash paid for amounts included in the measurement of lessee's operating lease liabilities. Operating lease cost: Operating Lease, Cost Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Cover [Abstract] Derivative Contract [Domain] Derivative Contract [Domain] Public Utilities General Disclosures [Table] Public Utilities General Disclosures [Table] Electric plant: Public Utilities, Property, Plant and Equipment, Net [Abstract] Equity Awards Adjustments Equity Awards Adjustments [Member] Deferred charges related to Vogtle Units No. 3 and No. 4 training costs Deferred charges related to Vogtle Units [Member] Deferred charges related to Vogtle Units Interest rate options cost Interest Rate Option Cost [Member] Discloses the amount of regulatory assets related to the deferral of net loss (gains) associated with the change in fair value of the interest rate options to hedge interest rates on expected borrowings of the entity. Total equity and liabilities Liabilities and Equity Regulatory Asset [Domain] Regulatory Asset [Domain] Member Power Bill Prepayments Member Power Bill Prepayments [Abstract] No definition available. Employee Stock Option Share-Based Payment Arrangement, Option [Member] Fair Value Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Construction work in progress Public Utilities, Property, Plant and Equipment, Construction Work in Progress Other current liabilities Increase (Decrease) in Other Operating Liabilities Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Smarr Combined Cycle Project Smarr Combined Cycle Project [Member] Smarr Combined Cycle Project Cumulative recovery of financing costs Electric Generation Revenue Cumulative Amount Recovered from Members Represents the cumulative amount recovered from members pursuant to rate management programs. Debt Debt Securities, Trading Tabular List, Table Tabular List [Table Text Block] Patronage capital and membership fees Patronage Capital And Membership Fees Retained net margin and cooperative membership fees. Two-unit Combined Cycle Generation Facility in Monroe County, Georgia Two-unit Combined Cycle Generation Facility in Monroe County, Georgia [Member] Two-unit Combined Cycle Generation Facility in Monroe County, Georgia Other Other Nonoperating Income (Expense) 2026 Settlement Or Maturity Period, Remainder Of Current Fiscal Year [Member] Settlement Or Maturity Period, Remainder Of Current Fiscal Year Accretion Accretion cost Asset Retirement Obligation, Accretion Expense Schedule of Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities [Table Text Block] Tabular disclosure of regulatory assets and liabilities. Regulatory assets represent certain costs that are probable of being recovered from members in the future revenues through rates under the wholesale power contracts with members of the reporting entity. Regulatory liabilities represent certain items of income that the entity is retaining and that will be applied in the future to reduce revenues required to be recovered from members of the reporting entity. Equity Equity Securities, FV-NI, Unrealized Loss Name Awards Close in Time to MNPI Disclosures, Individual Name Number of electric distribution cooperative members Number of electric distribution cooperative members Number Of Electric Distribution Cooperative Members Represents the number of electric distribution cooperative members. Increase (Decrease) in Members' Capital Increase (Decrease) in Members' Capital [Roll Forward] 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] Gains and (losses) on derivative instruments Derivative, Gain (Loss) on Derivative, Net [Abstract] Derivative instruments Derivatives, Fair Value [Line Items] Regulatory deferral of costs associated with nuclear decommissioning Nuclear Decommission Regulatory Deferral Costs Regulatory deferral of amounts required to adjust decommissioning fund earnings to equal nuclear accretion expense plus depreciation of related nuclear asset retirement obligations in the current period. Receivables Receivables, Net, Current Adjustment to Compensation: Adjustment to Compensation [Axis] Hawk Road Energy Facility Hawk Road [Member] Represents information pertaining to Hawk Road plant used in connection with the generation of combustion turbine energy wholly owned by the entity. Derivative Settlement or Maturity by Period [Domain] Derivative Settlement or Maturity by Period [Domain] Derivative Settlement or Maturity by Period [Domain] 2027 Settlement Or Maturity Period, Year One [Member] Represents the derivative contracts that are expected to settle or mature in 2020. Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Operating cash flows from finance leases Finance Lease, Interest Payment on Liability Interest (net of amounts capitalized) Interest Paid, Excluding Capitalized Interest, Operating Activity Property additions Payments to Acquire Productive Assets Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Right-of-use assets—Finance leases Finance Lease, Right-of-Use Asset [Abstract] n/a Restricted Investments Note [Abstract] Restricted Investments Note [Abstract] Credit Facility [Axis] Credit Facility [Axis] Rate management program, additional collection period Rate Management Program, Additional Collection Period The period of additional collections made to recover future expense on a current basis. Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities [Text Block] Lease Terms Through February 2042 Operating Lease Agreements With Terms Through February 2042 [Member] Represent information pertaining to operating lease agreements with terms through February 2042 Name Measure Name Accounts payable Accounts Payable, Current Pay vs Performance Disclosure [Line Items] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Other Other Noncash Income (Expense) Debt Instrument [Line Items] Debt Instrument [Line Items] Premium and loss on reacquired debt Premium And Loss On Reacquired Debt [Member] Represents premiums paid, together with unamortized transaction costs related to reacquired debt, treated as deferred charges for regulatory purposes. Energy revenues Energy Services [Member] Represents the revenue from energy services. Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Entity Filer Category Entity Filer Category Unrealized loss position Debt Securities, Available-for-Sale, Unrealized Loss Position Short-term investments Short-Term Investments Coal-fired maintenance outage costs Unamortized Deferred Coal Fired Outage Costs Net [Member] Coal-fired outage costs, accounted for as regulatory assets, are deferred and amortized on a straight-line basis to expense over an 18 to 36-month period. Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Restricted Cash and Short-Term Investments Restricted Assets Disclosure [Text Block] Name Trading Arrangement, Individual Name Other Other Deferred Costs, Net Cash and cash equivalents Cash and cash equivalents Cash and Cash Equivalent Finance Leases Finance Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract] Net Regulatory Assets Net Regulatory Assets Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Company Selected Measure Amount Company Selected Measure Amount Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] Development and construction of generation facility, budget Public Utilities, Development And Construction Of Generation Facility, Budget Public Utilities, Development And Construction Of Generation Facility, Budget Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] A table of assets and liabilities that are created when regulatory agencies permit public utilities to defer certain costs and recognition of certain revenues that are included in rate-setting to the balance sheet. Gross Unrealized Gains Debt and Equity Securities, Unrealized Gain [Abstract] n/a Rural Utilities Service Empowering Rural America (New ERA) Loan Rural Utilities Service Empowering Rural America (New ERA) Loan [Member] Rural Utilities Service Empowering Rural America (New ERA) Loan Current assets: Assets, Current [Abstract] Operating leases Operating Lease, Weighted Average Remaining Lease Term Net Carrying Value Presented on the Balance Sheet Derivative Liability Non-PEO NEO Non-PEO NEO [Member] Interest charges: Interest and Debt Expense [Abstract] 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 Award Timing Method Award Timing Method [Text Block] Net decrease 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 Forecast Forecast [Member] Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] 2028 Lessee, Finance Lease And Operating Lease, Liability, To Be Paid, Due Year Two Amount of lessee's undiscounted obligation for lease payments for finance lease and operating lease, due in second fiscal year following latest fiscal year. Other Other Securities, FV-NI, Cost Cost of investment in other securities measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value. Recently Issued or Adopted Accounting Pronouncements Accounting Standards Update and Change in Accounting Principle [Text Block] Net margin Net margin Net Income (Loss) Attributable to Parent Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Balance Sheet Location [Axis] Location, Statement of Financial Position, Balance [Axis] Member Capital Components [Domain] Member Capital Components [Domain] Components of members' equity are the parts of the total equity balance including that which is allocated to members' capital and accumulated other comprehensive income. Statement [Table] Statement [Table] Consolidated Statements of Patronage Capital and Membership Fees Consolidated Statements of Patronage Capital and Membership Fees [Abstract] Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Restatement Determination Date: Restatement Determination Date [Axis] 2026 Lessee, Finance Lease And Operating Lease, Liability, To Be Paid, Remainder Of Fiscal Year Amount of lessee's undiscounted obligation for lease payments for finance lease and operating lease having an initial or remaining lease term in excess of one year due in remainder of fiscal year following latest fiscal year. Receivables Increase (Decrease) in Receivables Assets Derivative Asset, Subject to Master Netting Arrangement, before Offset Receivables from contracts Contract with Customer, Asset, before Allowance for Credit Loss Operating revenues: Revenues [Abstract] Electric plant in service, net Public Utilities, Property Plant and Equipment, Plant in Service, Net Period end amount of total net property, plant and equipment plant in service. Credit collateral posted Collateral Already Posted, Aggregate Fair Value Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments and Hedging Activities Disclosure [Abstract]