Oglethorpe Power 10-Q 13 May 24 2024 Q1 Quarterly report Financial data

Cover Page

Cover Page	3 Months Ended
	Mar. 31, 2024 shares
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
Entity File Number	333-192954
Entity Registrant Name	OGLETHORPE POWER CORP
Entity Incorporation, State or Country Code	GA
Entity Tax Identification Number	58-1211925
Entity Address, Address Line One	2100 East Exchange Place
Entity Address, City or Town	Tucker
Entity Address, State or Province	GA
Entity Address, Postal Zip Code	30084-5336
City Area Code	770
Local Phone Number	270-7600
Entity Current Reporting Status	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	0
Entity Central Index Key	0000788816
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Electric plant:
In service	$ 14,202,485	$ 14,112,098
Right-of-use assets—finance leases	302,732	302,732
Less: Accumulated provision for depreciation	(5,487,672)	(5,418,738)
Electric plant in service, net	9,017,545	8,996,092
Nuclear fuel, at amortized cost	395,866	389,662
Construction work in progress	3,397,847	3,294,641
Total electric plant	12,811,258	12,680,395
Investments and funds:
Nuclear decommissioning trust fund	679,298	641,239
Investment in associated companies	83,794	82,133
Long-term investments	709,815	690,732
Other	36,088	35,585
Total investments and funds	1,508,995	1,449,689
Current assets:
Cash and cash equivalents	327,470	490,592
Short-term investments	135,341	143,931
Receivables	180,414	201,784
Inventories, at weighted average cost	329,414	337,045
Prepayments and other current assets	48,905	18,335
Total current assets	1,021,544	1,191,687
Deferred charges and other assets:
Regulatory assets	1,136,248	1,131,489
Prepayments to Georgia Power Company	14,871	13,722
Other	55,699	57,869
Total deferred charges	1,206,818	1,203,080
Total assets	16,548,615	16,524,851
Capitalization:
Patronage capital and membership fees	1,300,016	1,257,917
Long-term debt	11,474,583	11,600,917
Obligation under finance leases	43,586	43,586
Obligation under Rocky Mountain transactions	30,365	29,862
Other	4,786	5,152
Total capitalization	12,853,336	12,937,434
Current liabilities:
Long-term debt and finance leases due within one year	381,602	384,426
Short-term borrowings	662,779	607,885
Accounts payable	63,328	117,272
Accrued interest	121,073	106,355
Member power bill prepayments, current	25,842	31,406
Other current liabilities	113,493	111,109
Total current liabilities	1,368,117	1,358,453
Deferred credits and other liabilities:
Asset retirement obligations	1,537,803	1,458,937
Member power bill prepayments, non-current	70,033	47,133
Regulatory liabilities	704,084	706,320
Other	15,242	16,574
Total deferred credits and other liabilities	2,327,162	2,228,964
Total equity and liabilities	$ 16,548,615	$ 16,524,851

Consolidated Statements of Reve

Consolidated Statements of Revenues and Expenses (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating revenues:
Total operating revenues	$ 536,314	$ 389,453
Operating expenses:
Fuel	167,046	133,168
Production	118,090	93,467
Depreciation and amortization	94,105	72,674
Purchased power	19,220	17,630
Accretion	17,622	15,508
Total operating expenses	416,083	332,447
Operating margin	120,231	57,006
Other income:
Investment income	17,052	16,382
Other	2,804	2,925
Total other income	19,856	19,307
Interest charges:
Interest expense	129,391	123,707
Allowance for debt funds used during construction	(34,107)	(74,430)
Amortization of debt discount and expense	2,704	2,626
Net interest charges	97,988	51,903
Net margin	42,099	24,410
Sales to members
Operating revenues:
Total operating revenues	535,370	387,653
Sales to non-members
Operating revenues:
Total operating revenues	$ 944	$ 1,800

Consolidated Statements of Patr

Consolidated Statements of Patronage Capital and Membership Fees (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Increase (Decrease) in Members' Capital
Net margin	$ 42,099	$ 24,410
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Beginning balance	1,257,917	1,192,127
Net margin	42,099	24,410
Ending balance	$ 1,300,016	$ 1,216,537

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash flows from operating activities:
Net margin	$ 42,099	$ 24,410
Adjustments to reconcile net margin to net cash provided by operating activities:
Depreciation and amortization, including nuclear fuel	131,940	92,645
Accretion cost	17,622	15,508
Amortization of deferred gains	(447)	(447)
Allowance for equity funds used during construction	(347)	(149)
Deferred outage costs	(11,856)	(21,198)
Loss on sale of investments	471	1,289
Regulatory deferral of costs associated with nuclear decommissioning	(8,125)	(8,519)
Other	(14,480)	(1,043)
Change in operating assets and liabilities:
Receivables	26,609	49,887
Inventories	7,683	(17,711)
Prepayments and other current assets	(30,569)	4,027
Accounts payable	(49,628)	(116,354)
Accrued interest	14,718	(13,109)
Accrued taxes	(33,733)	(36,722)
Other current liabilities	24,494	(26,841)
Rate management program billing credits applied	(35,646)	(9,494)
Other	17,336	(989)
Total adjustments	56,042	(89,220)
Net cash provided by (used in) operating activities	98,141	(64,810)
Cash flows from investing activities:
Property additions	(174,270)	(285,233)
Activity in nuclear decommissioning trust fund—Purchases	(140,865)	(2,500)
Activity in nuclear decommissioning trust fund—Proceeds	136,894	283
Decrease in restricted investments	0	74,031
Activity in long-term and short-term investments—Purchases	(82,283)	(63,505)
Activity in other long-term investments—Proceeds	80,672	68,226
Other	(3,512)	8,163
Net cash used in investing activities	(183,364)	(200,535)
Cash flows from financing activities:
Long-term debt proceeds	6,067	15,431
Long-term debt payments	(136,047)	(137,732)
Increase in short-term borrowings, net	54,894	157,375
Other	(2,813)	11,311
Net cash (used in) provided by financing activities	(77,899)	46,385
Net decrease in cash, cash equivalents and restricted cash	(163,122)	(218,960)
Cash, cash equivalents and restricted cash at beginning of period	490,592	625,781
Cash, cash equivalents and restricted cash at end of period	327,470	406,821
Cash paid for—
Interest (net of amounts capitalized)	80,063	61,915
Supplemental disclosure of non-cash investing and financing activities:
Change in asset retirement obligations	65,149	87,509
Accrued property additions at end of period	$ 41,104	$ 69,557

General

General	3 Months Ended
	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
General	General. The consolidated financial statements included in this report have been prepared by us pursuant to the rules and regulations of the Securities and Exchange Commission. In the opinion of management, the information furnished in this report reflects all adjustments (which include only normal recurring adjustments) and estimates necessary to fairly state, in all material respects, our financial condition and results of operations for the three-month periods ended March 31, 2024 and 2023. Examples of estimates used include items related to (i) our asset retirement obligations, such as closure and post-closure cost estimates, timing of expenditures, escalation factors and discount rates, and (ii) depreciation rates, such as determining the depreciable service lives. Actual results may differ from those estimates. Certain information and footnote disclosures normally included in financial statements prepared in accordance with generally accepted accounting principles have been condensed or omitted pursuant to SEC rules and regulations, although we believe that the disclosures are adequate to make the information presented not misleading. Certain prior year amounts have been reclassified to conform with current year presentation. These unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements and the notes thereto included in our Annual Report on Form 10-K for the fiscal year ended December 31, 2023, as filed with the SEC. The results of operations for the three-month period ended March 31, 2024 are not necessarily indicative of results to be expected for the full year. As noted in our 2023 Form 10-K, our revenues consist primarily of sales to our 38 electric distribution cooperative members and, thus, the receivables on the consolidated balance sheets are principally from our members. See "Notes to Consolidated Financial Statements" in our 2023 Form 10-K.

Fair Value

Fair Value	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value	Fair Value. Authoritative guidance regarding fair value measurements for financial and non-financial assets and liabilities defines fair value, establishes a framework for measuring fair value in accordance with generally accepted accounting principles, and expands disclosures about fair value measurements. The guidance establishes a three-tier fair value hierarchy which prioritizes the inputs used in measuring fair value as follows: • Level 1. Quoted prices from active markets for identical assets or liabilities as of the reporting date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis. Quoted prices in active markets provide the most reliable evidence of fair value and are used to measure fair value whenever available. Level 1 primarily consists of financial instruments that are exchange-traded. • Level 2. Pricing inputs other than quoted prices in active markets included in Level 1, which are either directly or indirectly observable as of the reporting date. Level 2 includes financial instruments that are valued using models or other valuation methodologies. These models are primarily industry-standard models that consider various assumptions, including quoted forward prices for commodities, time value, volatility factors, and current market and contractual prices for the underlying instruments, as well as other relevant economic measures. Level 2 primarily consists of financial instruments that are non-exchange-traded but have significant observable inputs. • Level 3. Pricing inputs that include significant inputs which are generally less observable from objective sources. These inputs may include internally developed methodologies that result in management's best estimate of fair value. Level 3 financial instruments are those whose fair value is based on significant unobservable inputs. As required by the guidance, assets and liabilities measured at fair value are based on one or more of the following three valuation techniques: 1. Market approach. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable assets or liabilities (including a business) and deriving fair value based on these inputs. 2. Income approach. The income approach uses valuation techniques to convert future amounts (for example, cash flows or earnings) to a single present amount (discounted). The measurement is based on the value indicated by current market expectations about those future amounts. 3. Cost approach. The cost approach is based on the amount that currently would be required to replace the service capacity of an asset (often referred to as current replacement cost). This approach assumes that the fair value would not exceed what it would cost a market participant to acquire or construct a substitute asset of comparable utility, adjusted for obsolescence. The tables below detail assets and liabilities measured at fair value on a recurring basis at March 31, 2024 and December 31, 2023. Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs March 31, 2024 (Level 1) (Level 2) (Level 3) (dollars in thousands) Nuclear decommissioning trust funds: Domestic equity $ 259,404 $ 259,404 $ — $ — International equity trust 141,293 — 141,293 — Corporate bonds and debt 64,861 — 64,772 89 US Treasury securities 42,814 42,814 — — Mortgage backed securities 56,607 — 56,607 — Domestic mutual funds 92,626 92,626 — — Municipal bonds 303 — 303 — Federal agency securities 8,231 — 8,231 — International mutual funds 2,449 — 2,449 — Non-US Gov't bonds & private placements 3,708 — 3,708 — Other 7,002 7,002 — — Long-term investments: International equity trust 46,098 — 46,098 — Corporate bonds and debt 14,949 — 14,949 — US Treasury securities 14,783 14,783 — — Mortgage backed securities 17,068 — 17,068 — Domestic mutual funds 387,897 387,897 — — Treasury STRIPS 226,643 — 226,643 — Non-US Gov't bonds & private placements 1,775 — 1,775 — Other 602 602 — — Short-term investments: Treasury STRIPS 135,341 — 135,341 — Natural gas swaps 10,381 — 10,381 — Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs December 31, 2023 (Level 1) (Level 2) (Level 3) (dollars in thousands) Nuclear decommissioning trust funds: Domestic equity $ 234,979 $ 234,979 $ — $ — International equity trust 134,911 — 134,911 — Corporate bonds and debt 67,986 — 67,900 86 US Treasury securities 43,917 43,917 — — Mortgage backed securities 58,763 — 58,763 — Domestic mutual funds 85,481 85,481 — — Municipal bonds 303 — 303 — Federal agency securities 7,256 — 7,256 — Non-US Gov't bonds & private placements 2,717 — 2,717 — International mutual funds 2,012 — 2,012 — Other 2,914 2,914 — — Long-term investments: International equity trust 43,202 — 43,202 — Corporate bonds and debt 14,151 — 14,151 — US Treasury securities 17,243 17,243 — — Mortgage backed securities 15,024 — 15,024 — Domestic mutual funds 378,387 378,387 — — Treasury STRIPS 220,765 — 220,765 — Non-US Gov't bonds & private placements 1,568 — 1,568 — Other 392 392 — — Short-term investments: Treasury STRIPS 143,931 — 143,931 — Natural gas swaps 13,445 — 13,445 — The Level 2 investments above may not be exchange traded. The fair value measurements for these investments are based on a market approach, including the use of observable inputs at or near the valuation date. Common inputs include reported trades and broker/dealer bid/ask prices. The fair value of the Level 2 investments above in international equity trust are calculated based on the net asset value per share of the fund. There are no unfunded commitments for the international equity trust and redemption may occur daily with a 3-day redemption notice period. The Level 3 investments above in corporate bonds and debt consist of investments in bank loans which are not exchange traded. Although these securities may be liquid and priced daily, their inputs are not observable. The estimated fair values of our long-term debt, including current maturities at March 31, 2024 and December 31, 2023 were as follows: 2024 2023 Carrying Fair Carrying Fair (in thousands) Long-term debt $ 11,966,572 $ 10,233,768 $ 12,096,552 $ 10,638,749 The estimated fair value of long-term debt is classified as Level 2 and is estimated based on observed or quoted market prices for the same or similar issues or on current rates offered to us for debt of similar maturities. The primary sources of our long-term debt consist of first mortgage bonds, pollution control revenue bonds and long-term debt issued by the Federal Financing Bank that is guaranteed by the Rural Utilities Service or the U.S. Department of Energy. The valuations for the first mortgage bonds and the pollution control revenue bonds were obtained from a third party data reporting service, and are based on secondary market trading of our debt. Valuations for debt issued by the Federal Financing Bank are based on U.S. Treasury rates as of March 31, 2024 and December 31, 2023 plus an applicable spread, which reflects our borrowing rate for new loans of this type from the Federal Financing Bank. For cash and cash equivalents and receivables, the carrying amount approximates fair value because of the short-term maturity of those instruments.

Derivative Instruments

Derivative Instruments	3 Months Ended
	Mar. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	Derivative Instruments. We use commodity derivatives to manage our exposure to fluctuations in the market price of natural gas. Our risk management and compliance committee provides general oversight over all derivative activities. We do not apply hedge accounting to derivative transactions, but instead apply regulated operations accounting. Consistent with our rate-making, unrealized gains or losses on our natural gas swaps are reflected as regulatory assets or liabilities, as appropriate. Realized gains and losses on natural gas swaps are included in fuel expense within our consolidated statements of revenues and expenses and, therefore, net margins within our consolidated statement of cash flows. We are exposed to credit risk as a result of entering into these arrangements. Credit risk is the potential loss resulting from a counterparty's nonperformance under an agreement. We have established policies and procedures to manage credit risk through counterparty analysis, exposure calculation and monitoring, exposure limits, collateralization and certain other contractual provisions. It is possible that volatility in commodity prices could cause us to have credit risk exposures with one or more counterparties. If such counterparties fail to perform their obligations, we could suffer a financial loss. However, as of March 31, 2024, all of the counterparties with transaction amounts outstanding under our derivative programs are rated investment grade by the major rating agencies or have provided a guaranty from one of their affiliates that is rated investment grade. We have entered into International Swaps and Derivatives Association agreements with our natural gas derivative counterparties that mitigate credit exposure by creating contractual rights relating to creditworthiness, collateral, termination and netting (which, in certain cases, allows us to use the net value of affected transactions with the same counterparty in the event of default by the counterparty or early termination of the agreement). Additionally, we have implemented procedures to monitor the creditworthiness of our counterparties and to evaluate nonperformance in valuing counterparty positions. We have contracted with a third party to assist in monitoring certain of our counterparties' credit standing and condition. Net liability positions are generally not adjusted as we use derivative transactions as hedges and have the ability and intent to perform under each of our contracts. In the instance of net asset positions, we consider general market conditions and the observable financial health and outlook of specific counterparties, forward looking data such as credit default swaps, when available, and historical default probabilities from credit rating agencies in evaluating the potential impact of nonperformance risk to derivative positions. The contractual agreements contain provisions that could require us or the counterparty to post collateral or credit support. The amount of collateral or credit support that could be required is calculated as the difference between the aggregate fair value of the hedges and pre-established credit thresholds. The credit thresholds are contingent upon each party's credit ratings from the major credit rating agencies. The collateral and credit support requirements vary by contract and by counterparty. Under the natural gas swap arrangements, we pay the counterparty a fixed price for specified natural gas quantities and receive a payment for such quantities based on a market price index. These payment obligations are netted, such that if the market price index is lower than the fixed price, we will make a net payment, and if the market price index is higher than the fixed price, we will receive a net payment. At March 31, 2024 and December 31, 2023, the estimated fair values of our natural gas contracts were net assets of approximately $10,381,000 and $13,445,000, respectively. At March 31, 2024 and December 31, 2023, none of our counterparties was required to post credit collateral under our natural gas swap agreeme nts. The following table reflects the notional volume of our natural gas derivatives as of March 31, 2024 that is expected to settle or mature each year: Year Natural Gas Swaps (MMBTUs) (in millions) 2024 29.4 2025 25.2 2026 20.9 2027 10.3 2028 0.5 Total 86.3 The table below reflects the fair value of derivative instruments and their effect on our consolidated balance sheets at March 31, 2024 and December 31, 2023. Balance Sheet Location Fair Value 2024 2023 (dollars in thousands) Assets: Natural gas swaps Other deferred charges $ 23,698 $ 25,459 Liabilities: Natural gas swaps Other current liabilities $ 12,688 $ 10,370 Natural gas swaps Other deferred credits $ 629 $ 1,644 The following table presents the gross realized gains and (losses) on derivative instruments recognized in net margins for the three months ended March 31, 2024 and 2023. Statement of Three Months Ended March 31, 2024 2023 (dollars in thousands) Natural gas swaps gains Fuel $ 41 $ 135 Natural gas swaps losses Fuel (8,452) (9,397) Total $ (8,411) $ (9,262) The following table presents the unrealized gains on derivative instruments deferred on the balance sheet at March 31, 2024 and December 31, 2023. Balance Sheet Location 2024 2023 (dollars in thousands) Natural gas swaps Regulatory liability $ 10,381 $ 13,445 Total $ 10,381 $ 13,445

Investment Securities

Investment Securities	3 Months Ended
	Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Investment Securities	Investment Securities. Investment securities we hold are recorded at fair value in the accompanying consolidated balance sheets. We apply regulated operations accounting to the unrealized gains and losses of all investment securities. All realized and unrealized gains and losses are determined using the specific identification method. The following tables summarize debt and equity securities as of March 31, 2024 and December 31, 2023. Gross Unrealized (dollars in thousands) March 31, 2024 Cost Gains Losses Fair Equity $ 350,947 $ 292,940 $ (6,033) $ 637,854 Debt 903,715 2,574 (27,229) 879,060 Other 7,549 1 (10) 7,540 Total $ 1,262,211 $ 295,515 $ (33,272) $ 1,524,454 Gross Unrealized (dollars in thousands) December 31, 2023 Cost Gains Losses Fair Equity $ 344,669 $ 246,795 $ (5,549) $ 585,915 Debt 908,316 3,938 (25,181) 887,073 Other 2,889 61 (36) 2,914 Total $ 1,255,874 $ 250,794 $ (30,766) $ 1,475,902 The cost basis of our debt securities that were in unrealized loss positions at March 31, 2024 was $832,901,000. At March 31, 2024, $3,322,000 of the $27,229,000 of unrealized losses relates to securities that have been in unrealized loss positions for less than twelve months and $23,907,000 relates to securities that have been in unrealized loss positions for greater than twelve months. These unrealized losses are primarily attributable to increases in market interest rates. The cost basis of our debt securities that were in unrealized loss positions at December 31, 2023 was $788,798,000. At December 31, 2023, $3,362,000 of the $25,181,000 of unrealized losses relates to securities that have been in unrealized loss positions for less than twelve months and $21,819,000 relates to securities that have been in unrealized loss positions for greater than twelve months. These unrealized losses are primarily attributable to increases in market interest rates.

Recently Issued or Adopted Acco

Recently Issued or Adopted Accounting Pronouncements	3 Months Ended
	Mar. 31, 2024
Accounting Standards Update and Change in Accounting Principle [Abstract]
Recently Issued or Adopted Accounting Pronouncements	Recently Issued or Adopted Accounting Pronouncements. In November 2023, the Financial Accounting Standards Board (FASB) issued “Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures.” The amendments in this update are intended to improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant expenses. The amendments in this update require disclosures to include significant segment expenses that are regularly provided to the chief operating decision maker (CODM), a description of other segment items by reportable segment, and any additional measures of a segment's profit or loss used by the CODM when deciding how to allocate resources. The amendments in this update are also applicable to entities with only one reportable segment. The amendments in this update also require all annual disclosures currently required by Topic 280 to be included in interim periods. The new standard is effective for us for annual reporting periods beginning after December 15, 2023 and interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted and requires retrospective application to all prior periods presented in the financial statements. We are currently evaluating the future impact of this standard on our consolidated financial statements. In December 2023, the FASB amended "Income Taxes (Topic 740): Improvements to Income Tax Disclosures”. The amendments in this update requires additional disclosures related to the rate reconciliation, income taxes paid and other amendments intended to improve effectiveness and comparability. The amendments in this update are effective for us for annual periods beginning after December 15, 2024. Early adoption is permitted and should be applied on a prospective basis. Retrospective application is permitted. We are currently evaluating the future impact of this standard on our consolidated financial statements, however, we do not anticipate the impact will be significant.

Revenue Recognition

Revenue Recognition	3 Months Ended
	Mar. 31, 2024
Revenue from Contract with Customer [Abstract]
Revenue Recognition	Revenue Recognition. As an electric membership cooperative, our principal business is providing wholesale electric service to our members. Our operating revenues are derived primarily from wholesale power contracts we have with each of our 38 members that extend to December 31, 2085. These contracts are substantially identical and obligate our members jointly and severally to pay all expenses associated with owning and operating our power supply business. As a cooperative, we operate on a not-for-profit basis and, accordingly, seek only to generate revenues sufficient to recover our cost of service and to generate margins sufficient to establish reasonable reserves and meet certain financial coverage requirements. We also sell energy and capacity to non-members through industry standard contracts and negotiated agreements, respectively. We do not have multiple operating segments. Pursuant to our contracts, we primarily provide two services, capacity and energy. Capacity and energy revenues are recognized by us upon transfer of control of promised services to our members and non-members in an amount that reflects the consideration we expect to receive in exchange for those services. Capacity and energy are distinct and we account for them as separate performance obligations. The obligations to provide capacity and energy are satisfied over time as the customer simultaneously receives and consumes the benefit of these services. Both performance obligations are provided directly by us and not through a third party. Each of our members is obligated to pay us for capacity and energy we furnish under the wholesale power contract in accordance with rates we establish. We review our rates periodically but are required to do so at least once every year. Revenues from our members are derived through a cost-plus rate structure which is set forth as a formula in the rate schedule to the wholesale power contracts. The formulary rate provides for the pass-through of our (i) fixed costs (net of any income from other sources) plus a targeted margin as capacity revenues and (ii) variable costs as energy revenues from our members. Power purchase and sale agreements between us and non-members obligate each non-member to pay us for capacity, if any, and energy furnished in accordance with the prices mutually agreed upon. Margins produced from non-member sales are included in our rate schedule formula and reduce revenue requirements from our members. As of March 31, 2024 and December 31, 2023, we did not have any significant long-term contracts with non-members. The consideration we receive for providing capacity services is determined by our formulary rate on an annual basis. The components of the formulary rate associated with capacity costs include the annual budget of fixed costs, a targeted margin and income from other sources. Capacity revenues, therefore, vary to the extent these components vary. Fixed costs include items such as fixed operation and maintenance expenses, administrative and general expenses, depreciation and interest. Year to year, capacity revenue fluctuations are generally due to the recovery of fixed operation and maintenance expenses. Fixed costs also include certain costs, such as major maintenance costs, which will be recognized as expense in future periods. Recognition of revenues associated with these future expenses is deferred pursuant to Accounting Standards Codification (ASC) 980, Regulated Operations. The regulatory liabilities are amortized to revenue in accordance with the associated revenue deferral plan as the expenses are recognized. For information regarding regulatory accounting, see Note J. Capacity revenues are recognized by us for standing ready to deliver electricity to our customers. Our capacity revenues are based on the associated costs we expect to recover in a given year and are generally recognized and billed to our members in equal monthly installments over the course of the year regardless of whether our generation and purchased power resources are dispatched to produce electricity. Non-member capacity revenues are billed and recognized in accordance with the terms of the associated contract. We have a power bill prepayment program pursuant to which our members may prepay future capacity costs and receive a discount. As this program provides us with financing, we adjust our capacity revenues by the amount of the discount, which is based on our avoided cost of borrowing. For additional information regarding our member prepayment program, see Note K. We satisfy our performance obligations to deliver energy as energy is delivered to the applicable meter points. We determine the standard selling price for energy we deliver to our members based upon the variable costs incurred to generate or purchase that energy. Fuel expense is the primary variable cost. Energy revenue recognized equals the actual variable expenses incurred in any given accounting period. Our member energy revenues fluctuate from period to period based on several factors, including fuel costs, weather and other seasonal factors, load requirements in our members' service territories, variable operating costs, the availability of electric generation resources, our decisions of whether to dispatch our owned or purchased resources or member-owned resources over which we have dispatch rights, and by members' decisions of whether to purchase a portion of their hourly energy requirements from our resources or from other suppliers. The standard selling price for our energy revenues from non-members is the price mutually agreed upon. We are required under our first mortgage indenture to produce a margins for interest ratio of at least 1.10 for each fiscal year. For 2024, our board has approved a targeted margins for interest ratio of 1.14. Historically, our board of directors has approved adjustments to revenue requirements by year end such that revenue in excess of that required to meet the targeted margins for interest ratio is refunded to the members. Given that our capacity revenues are based upon budgeted expenditures and generally recognized and billed to our members in equal monthly installments over the course of the year, we may recognize capacity revenues that exceed our actual fixed costs and targeted margins in any given interim reporting period. At each interim reporting period we assess our projected revenue requirements through year end to determine whether a refund to our members of excess consideration is likely. If so, we reduce our capacity revenues and recognize a refund liability to our members. Refund liabilities, if any, are included in accounts payable on our unaudited consolidated balance sheets. As of March 31, 2024, we did not recognize a refund liability. As of December 31, 2023, we recognized refund liabilities totaling $34,266,000. Based on our current agreements with non-members, we do not refund any consideration received from non-members. Sales to members for the three months ended March 31, 2024 and 2023 were as follows: Three Months Ended (dollars in thousands) 2024 2023 Capacity revenues $ 355,718 $ 242,043 Energy revenues 179,652 145,610 Total $ 535,370 $ 387,653 Receivables from contracts with our members at March 31, 2024 and December 31, 2023 were $147,851,000 and $170,901,000, respectively. Sales to non-members during the three months ended March 31, 2024 and 2023 were as follows: Three Months Ended (dollars in thousands) 2024 2023 Energy revenues $ 158 $ 1,037 Capacity revenues 786 763 Total $ 944 $ 1,800 Energy revenues from non-members for the three months ended March 31, 2024 and March 31, 2023 were primarily from the sale of the BC Smith deferring members' output into the wholesale market. For the three months ended March 31, 2024 and March 31, 2023, we also recognized capacity revenues from non-members related to the two units we acquired at the Washington County Power Plant in December 2022. The remainder of our receivables is primarily related to transactions with Georgia Power, affiliated companies and investment income. Our receivables from non-members at March 31, 2024 and December 31, 2023 were $32,563,000 and $30,883,000, respectively. Electric capacity and energy revenues are recognized by us without any obligation for returns, warranties or taxes collected. As our members are jointly and severally obligated to pay all expenses associated with owning and operating our power supply business and we perform an on-going assessment of the credit worthiness of non-members and have not had a history of any write-offs from non-members, we have not recorded an allowance for doubtful accounts associated with our receivables from members or non-members. We have a rate management program that ended December 2023, which allowed us to expense and recover interest costs associated with the construction of Vogtle Units No. 3 and No. 4, on a current basis, that would otherwise be deferred or capitalized. The subscribing members of Vogtle Units No. 3 and No. 4 elected to participate in this program on an annual basis. Under this program, the amount billed to participating members during the three months ended March 31, 2023 was $1,761,000. The cumulative amount billed since inception of the program totaled $135,693,000. In 2018, we began an additional rate management program that allowed us to recover future expense on a current basis from our members. In general, the program allowed for additional collections over a five-year period with those amounts then applied to billings over the subsequent five-year period. The program is designed primarily as a mechanism to assist our members in managing the rate impacts associated with the commercial operation of the new Vogtle units. During the first quarter of 2022, we began applying billing credits to some of our participating members within this program. In December 2022, collections from our members ended for this rate management program. Under this program, net billing credits to participating members during the three months ended March 31, 2024 and 2023 were $30,409,000 and $15,713,000, respectively. Funds collected through this program are invested and held until applied to members' bills. Investments that mature and are expected to be applied to members' bills within the next twelve months are included in the Short-term investments line item within our unaudited consolidated balance sheets. In conjunction with this program, we applied regulated operations accounting to defer these revenues and related investment income on the funds collected. Amounts deferred under the program are amortized to income when applied to members' bills. The net cumulative amount billed, since inception of the program totaled $369,102,000. As of March 31, 2024, $279,467,000 is our remaining liability to be credited to our members' bills. For additional information regarding our revenue deferral plan, see Note J.

Leases

Leases	3 Months Ended
	Mar. 31, 2024
Leases [Abstract]
Leases	Leases. As a lessee, we have a relatively small portfolio of leases with the most significant being our 60% undivided interest in Scherer Unit No. 2 and railcar leases for the transportation of coal. We also have various other leases of minimal value. We classify our four Scherer Unit No. 2 leases as finance leases and our railcar leases as operating leases. We have made an accounting policy election not to recognize right-of-use assets and lease liabilities that arise from short-term leases, leases having an initial term of 12 months or less, for any class of underlying asset. We recognize lease expense for short-term leases on a straight-line basis over the lease term. Lease expense recognized for our short-term leases during the three months ended March 31, 2024 and 2023 was insignificant. Finance Leases Three of our Scherer Unit No. 2 finance leases have lease terms through December 31, 2027, and one lease extends through June 30, 2031. At the end of the leases, we can elect at our sole discretion to: • Renew the leases for a period of not less than one year and not more than five years at fair market value, • Purchase the undivided interest at fair market value, or • Redeliver the undivided interest to the lessors. For rate-making purposes, we include the actual lease payments for our finance leases in our cost of service. The difference between lease payments and the aggregate of the amortization on the right-of-use asset and the interest on the finance lease obligation is recognized as a regulatory asset. Finance lease amortization is recorded in depreciation and amortization expense. Operating Leases Our railcar operating leases have terms that extend through November 30, 2028. At the end of the railcar operating leases, we can renew at terms mutually agreeable by us and the lessors, purchase the assets or return the assets to the lessors. We have additional operating leases including one for office equipment that has a term extending through October 31, 2028 and one for real property at one of our electric generating facilities that has a term extending through February 2042 with one renewal option for a 20 year term. The exercise of renewal options for our finance and operating leases is at our sole discretion. As all of our operating leases do not provide an implicit rate, we use an incremental borrowing rate based on the information available at the time new lease agreements are entered into or reassessed to determine the present value of lease payments. We combine lease and nonlease components for all lease agreements. Classification March 31, 2024 December 31, 2023 (dollars in thousands) Right-of-use assets—Finance leases Right-of-use assets $ 302,732 $ 302,732 Less: Accumulated provision for depreciation (279,465) (278,586) Total finance lease assets $ 23,267 $ 24,146 Lease liabilities—Finance leases Obligations under finance leases $ 43,586 $ 43,586 Long-term debt and finance leases due within one year 9,351 9,351 Total finance lease liabilities $ 52,937 $ 52,937 Classification March 31, 2024 December 31, 2023 (dollars in thousands) Right-of-use assets—Operating leases Electric plant in service, net $ 6,181 $ 6,587 Total operating lease assets $ 6,181 $ 6,587 Lease liabilities—Operating leases Capitalization—Other $ 4,786 $ 5,152 Other current liabilities 1,395 1,529 Total operating lease liabilities $ 6,181 $ 6,681 Three months ended Lease Cost Classification March 31, 2024 March 31, 2023 (dollars in thousands) Finance lease cost: Amortization of leased assets Depreciation and amortization $ 2,338 $ 2,099 Interest on lease liabilities Interest expense 1,400 1,638 Operating lease cost: Inventory (1) & production expense 538 329 Total leased cost $ 4,276 $ 4,066 (1) The majority of our operating lease costs relate to our railcar leases and such costs are added to the cost of our fossil-fuel inventories and are recognized in fuel expense as the inventories are consumed. March 31, 2024 December 31, 2023 Lease Term and Discount Rate: Weighted-average remaining lease term (in years) Finance leases 5.01 5.26 Operating leases 5.70 5.77 Weighted-average discount rate: Finance leases 11.05 % 11.05 % Operating leases 6.45 % 6.37 % Three months ended March 31, 2024 2023 (dollars in thousands) Other Information: Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating leases $ 632 $ 409 Right-of-use assets obtained in exchange for new operating lease liabilities $ 17 $ — Maturity analysis of our finance and operating lease liabilities as of March 31, 2024 is as follows: (dollars in thousands) Year Ending December 31, Finance Leases Operating Leases Total 2024 $ 14,949 $ 1,334 $ 16,283 2025 14,949 1,708 16,657 2026 14,949 1,416 16,365 2027 14,949 1,139 16,088 2028 3,052 1,029 4,081 Thereafter 7,633 723 8,356 Total lease payments $ 70,481 $ 7,349 $ 77,830 Less: imputed interest (17,544) (1,168) (18,712) Present value of lease liabilities $ 52,937 $ 6,181 $ 59,118 As a lessor, we primarily lease office space to several tenants within our headquarters building. Several of these tenants are related parties. We account for all of these lease agreements as operating leases. Lease income recognized during the three months ended March 31, 2024 and 2023 was as follows: Three Months Ended March 31, 2024 2023 (dollars in thousands) Lease income $ 1,387 $ 1,685
Leases	Leases. As a lessee, we have a relatively small portfolio of leases with the most significant being our 60% undivided interest in Scherer Unit No. 2 and railcar leases for the transportation of coal. We also have various other leases of minimal value. We classify our four Scherer Unit No. 2 leases as finance leases and our railcar leases as operating leases. We have made an accounting policy election not to recognize right-of-use assets and lease liabilities that arise from short-term leases, leases having an initial term of 12 months or less, for any class of underlying asset. We recognize lease expense for short-term leases on a straight-line basis over the lease term. Lease expense recognized for our short-term leases during the three months ended March 31, 2024 and 2023 was insignificant. Finance Leases Three of our Scherer Unit No. 2 finance leases have lease terms through December 31, 2027, and one lease extends through June 30, 2031. At the end of the leases, we can elect at our sole discretion to: • Renew the leases for a period of not less than one year and not more than five years at fair market value, • Purchase the undivided interest at fair market value, or • Redeliver the undivided interest to the lessors. For rate-making purposes, we include the actual lease payments for our finance leases in our cost of service. The difference between lease payments and the aggregate of the amortization on the right-of-use asset and the interest on the finance lease obligation is recognized as a regulatory asset. Finance lease amortization is recorded in depreciation and amortization expense. Operating Leases Our railcar operating leases have terms that extend through November 30, 2028. At the end of the railcar operating leases, we can renew at terms mutually agreeable by us and the lessors, purchase the assets or return the assets to the lessors. We have additional operating leases including one for office equipment that has a term extending through October 31, 2028 and one for real property at one of our electric generating facilities that has a term extending through February 2042 with one renewal option for a 20 year term. The exercise of renewal options for our finance and operating leases is at our sole discretion. As all of our operating leases do not provide an implicit rate, we use an incremental borrowing rate based on the information available at the time new lease agreements are entered into or reassessed to determine the present value of lease payments. We combine lease and nonlease components for all lease agreements. Classification March 31, 2024 December 31, 2023 (dollars in thousands) Right-of-use assets—Finance leases Right-of-use assets $ 302,732 $ 302,732 Less: Accumulated provision for depreciation (279,465) (278,586) Total finance lease assets $ 23,267 $ 24,146 Lease liabilities—Finance leases Obligations under finance leases $ 43,586 $ 43,586 Long-term debt and finance leases due within one year 9,351 9,351 Total finance lease liabilities $ 52,937 $ 52,937 Classification March 31, 2024 December 31, 2023 (dollars in thousands) Right-of-use assets—Operating leases Electric plant in service, net $ 6,181 $ 6,587 Total operating lease assets $ 6,181 $ 6,587 Lease liabilities—Operating leases Capitalization—Other $ 4,786 $ 5,152 Other current liabilities 1,395 1,529 Total operating lease liabilities $ 6,181 $ 6,681 Three months ended Lease Cost Classification March 31, 2024 March 31, 2023 (dollars in thousands) Finance lease cost: Amortization of leased assets Depreciation and amortization $ 2,338 $ 2,099 Interest on lease liabilities Interest expense 1,400 1,638 Operating lease cost: Inventory (1) & production expense 538 329 Total leased cost $ 4,276 $ 4,066 (1) The majority of our operating lease costs relate to our railcar leases and such costs are added to the cost of our fossil-fuel inventories and are recognized in fuel expense as the inventories are consumed. March 31, 2024 December 31, 2023 Lease Term and Discount Rate: Weighted-average remaining lease term (in years) Finance leases 5.01 5.26 Operating leases 5.70 5.77 Weighted-average discount rate: Finance leases 11.05 % 11.05 % Operating leases 6.45 % 6.37 % Three months ended March 31, 2024 2023 (dollars in thousands) Other Information: Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating leases $ 632 $ 409 Right-of-use assets obtained in exchange for new operating lease liabilities $ 17 $ — Maturity analysis of our finance and operating lease liabilities as of March 31, 2024 is as follows: (dollars in thousands) Year Ending December 31, Finance Leases Operating Leases Total 2024 $ 14,949 $ 1,334 $ 16,283 2025 14,949 1,708 16,657 2026 14,949 1,416 16,365 2027 14,949 1,139 16,088 2028 3,052 1,029 4,081 Thereafter 7,633 723 8,356 Total lease payments $ 70,481 $ 7,349 $ 77,830 Less: imputed interest (17,544) (1,168) (18,712) Present value of lease liabilities $ 52,937 $ 6,181 $ 59,118 As a lessor, we primarily lease office space to several tenants within our headquarters building. Several of these tenants are related parties. We account for all of these lease agreements as operating leases. Lease income recognized during the three months ended March 31, 2024 and 2023 was as follows: Three Months Ended March 31, 2024 2023 (dollars in thousands) Lease income $ 1,387 $ 1,685
Leases	Leases. As a lessee, we have a relatively small portfolio of leases with the most significant being our 60% undivided interest in Scherer Unit No. 2 and railcar leases for the transportation of coal. We also have various other leases of minimal value. We classify our four Scherer Unit No. 2 leases as finance leases and our railcar leases as operating leases. We have made an accounting policy election not to recognize right-of-use assets and lease liabilities that arise from short-term leases, leases having an initial term of 12 months or less, for any class of underlying asset. We recognize lease expense for short-term leases on a straight-line basis over the lease term. Lease expense recognized for our short-term leases during the three months ended March 31, 2024 and 2023 was insignificant. Finance Leases Three of our Scherer Unit No. 2 finance leases have lease terms through December 31, 2027, and one lease extends through June 30, 2031. At the end of the leases, we can elect at our sole discretion to: • Renew the leases for a period of not less than one year and not more than five years at fair market value, • Purchase the undivided interest at fair market value, or • Redeliver the undivided interest to the lessors. For rate-making purposes, we include the actual lease payments for our finance leases in our cost of service. The difference between lease payments and the aggregate of the amortization on the right-of-use asset and the interest on the finance lease obligation is recognized as a regulatory asset. Finance lease amortization is recorded in depreciation and amortization expense. Operating Leases Our railcar operating leases have terms that extend through November 30, 2028. At the end of the railcar operating leases, we can renew at terms mutually agreeable by us and the lessors, purchase the assets or return the assets to the lessors. We have additional operating leases including one for office equipment that has a term extending through October 31, 2028 and one for real property at one of our electric generating facilities that has a term extending through February 2042 with one renewal option for a 20 year term. The exercise of renewal options for our finance and operating leases is at our sole discretion. As all of our operating leases do not provide an implicit rate, we use an incremental borrowing rate based on the information available at the time new lease agreements are entered into or reassessed to determine the present value of lease payments. We combine lease and nonlease components for all lease agreements. Classification March 31, 2024 December 31, 2023 (dollars in thousands) Right-of-use assets—Finance leases Right-of-use assets $ 302,732 $ 302,732 Less: Accumulated provision for depreciation (279,465) (278,586) Total finance lease assets $ 23,267 $ 24,146 Lease liabilities—Finance leases Obligations under finance leases $ 43,586 $ 43,586 Long-term debt and finance leases due within one year 9,351 9,351 Total finance lease liabilities $ 52,937 $ 52,937 Classification March 31, 2024 December 31, 2023 (dollars in thousands) Right-of-use assets—Operating leases Electric plant in service, net $ 6,181 $ 6,587 Total operating lease assets $ 6,181 $ 6,587 Lease liabilities—Operating leases Capitalization—Other $ 4,786 $ 5,152 Other current liabilities 1,395 1,529 Total operating lease liabilities $ 6,181 $ 6,681 Three months ended Lease Cost Classification March 31, 2024 March 31, 2023 (dollars in thousands) Finance lease cost: Amortization of leased assets Depreciation and amortization $ 2,338 $ 2,099 Interest on lease liabilities Interest expense 1,400 1,638 Operating lease cost: Inventory (1) & production expense 538 329 Total leased cost $ 4,276 $ 4,066 (1) The majority of our operating lease costs relate to our railcar leases and such costs are added to the cost of our fossil-fuel inventories and are recognized in fuel expense as the inventories are consumed. March 31, 2024 December 31, 2023 Lease Term and Discount Rate: Weighted-average remaining lease term (in years) Finance leases 5.01 5.26 Operating leases 5.70 5.77 Weighted-average discount rate: Finance leases 11.05 % 11.05 % Operating leases 6.45 % 6.37 % Three months ended March 31, 2024 2023 (dollars in thousands) Other Information: Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating leases $ 632 $ 409 Right-of-use assets obtained in exchange for new operating lease liabilities $ 17 $ — Maturity analysis of our finance and operating lease liabilities as of March 31, 2024 is as follows: (dollars in thousands) Year Ending December 31, Finance Leases Operating Leases Total 2024 $ 14,949 $ 1,334 $ 16,283 2025 14,949 1,708 16,657 2026 14,949 1,416 16,365 2027 14,949 1,139 16,088 2028 3,052 1,029 4,081 Thereafter 7,633 723 8,356 Total lease payments $ 70,481 $ 7,349 $ 77,830 Less: imputed interest (17,544) (1,168) (18,712) Present value of lease liabilities $ 52,937 $ 6,181 $ 59,118 As a lessor, we primarily lease office space to several tenants within our headquarters building. Several of these tenants are related parties. We account for all of these lease agreements as operating leases. Lease income recognized during the three months ended March 31, 2024 and 2023 was as follows: Three Months Ended March 31, 2024 2023 (dollars in thousands) Lease income $ 1,387 $ 1,685

Contingencies and Regulatory Ma

Contingencies and Regulatory Matters	3 Months Ended
	Mar. 31, 2024
Contingencies and Regulatory Matters
Contingencies and Regulatory Matters	Contingencies and Regulatory Matters. We do not anticipate that the liabilities, if any, for any current proceedings against us will have a material effect on our financial condition or results of operations. However, at this time, the ultimate outcome of any pending or potential litigation cannot be determined. Environmental Matters. As is typical for electric utilities, we are subject to various federal, state and local environmental laws which represent significant future risks and uncertainties. Air emissions, water discharges and water usage are extensively controlled, closely monitored and periodically reported. Handling and disposal requirements govern the manner of transportation, storage and disposal of various types of waste. We may also become subject to climate change regulations that impose restrictions on emissions of greenhouse gases, including carbon dioxide. Such requirements may substantially increase the cost of electric service, by requiring modifications in the design or operation of existing facilities or the purchase of emission allowances. Failure to comply with these requirements could result in civil and criminal penalties and could include the complete shutdown of individual generating units not in compliance. Certain of our debt instruments require us to comply in all material respects with laws, rules, regulations and orders imposed by applicable governmental authorities, which include current and future environmental laws or regulations. Should we fail to be in compliance with these requirements, it would constitute a default under those debt instruments. We believe that we are in compliance with those environmental regulations currently applicable to our business and operations. Although it is our intent to comply with current and future regulations, we cannot provide assurance that we will always be in compliance. At this time, the ultimate impact of any new and more stringent environmental regulations described above is uncertain and could have an effect on our financial condition, results of operations and cash flows as a result of future additional capital expenditures and increased operations and maintenance costs. Additionally, litigation over environmental issues and claims of various types, including property damage, personal injury, common law nuisance, and citizen enforcement of environmental requirements such as air quality and water standards, has increased generally throughout the United States. In particular, personal injury and other claims for damages caused by alleged exposure to hazardous materials, and common law nuisance claims for injunctive relief, personal injury and property damage allegedly caused by coal combustion residue, greenhouse gas and other emissions have become more frequent. In July 2020, a group of individual plaintiffs filed a complaint, which was amended in December 2022, in the Superior Court of Fulton County, Georgia against Georgia Power alleging that the construction and operation of Plant Scherer, of which we are a co-owner, has impacted groundwater, surface water, and air, resulting in alleged personal injuries and property damage. The plaintiffs seek an unspecified amount of monetary damages including punitive damages, a medical monitoring fund, and injunctive relief. In December 2022, the Superior Court of Fulton County granted Georgia Power’s motion to transfer the case to the Superior Court of Monroe County. In May 2023, the Superior Court of Monroe County denied Georgia Power’s motion to dismiss the case for lack of subject matter jurisdiction. In July 2023, the Superior Court of Monroe County denied the remaining motions to dismiss certain claims and plaintiffs that Georgia Power filed at the outset of the case. On March 11, 2024, Georgia Power filed a motion to dismiss certain claims. On March 14, 2024, Georgia Power filed motions for summary judgment. The Superior Court of Monroe County has set a trial date of August 12, 2024 for the first of the approximately 44 plaintiffs. Eight additional complaints, three on October 8, 2021, four on February 7, 2022, and one on January 9, 2023, were filed in the Superior Court of Monroe County, Georgia against Georgia Power alleging that releases from Plant Scherer have impacted groundwater and air, resulting in alleged personal injuries and property damage. The plaintiffs sought an unspecified amount of monetary damages including punitive damages. After Georgia Power removed each of these cases to the U.S. District Court for the Middle District of Georgia, the plaintiffs voluntarily dismissed their complaints without prejudice in November 2022 and February 2023. On May 12, 2023, the plaintiffs refiled their eight complaints in the Superior Court of Monroe County. Also on May 12, 2023, a new complaint was filed in the Superior Court of Monroe County, Georgia against Georgia Power alleging that the construction and operation of Plant Scherer have impacted groundwater and air, resulting in alleged personal injuries. The plaintiff seeks an unspecified amount of monetary damages, including punitive damages. On May 18, 2023, Georgia Power removed all of these cases to the U.S. District Court for the Middle District of Georgia. The plaintiffs are requesting the court remand the cases back to the Superior Court of Monroe County. The amount of any possible losses from these matters cannot be estimated at this time.

Restricted Cash and Investments

Restricted Cash and Investments	3 Months Ended
	Mar. 31, 2024
Restricted Investments Note [Abstract]
Restricted Cash and Investments	Restricted Cash and Investments. Restricted cash consists of collateral posted by our counterparties under our natural gas swap agreements. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the unaudited consolidated balance sheets that sum to the total of the same such amounts reported in the unaudited consolidated statements of cash flows. Classification Three months ended March 31, 2024 March 31, 2023 (dollars in thousands) Cash and cash equivalents $ 327,470 $ 390,821 Restricted cash included in restricted cash and short-term investments — 16,000 Total cash, cash equivalents and restricted cash reported in the consolidated statements of cash flows $ 327,470 $ 406,821

Regulatory Assets and Liabiliti

Regulatory Assets and Liabilities	3 Months Ended
	Mar. 31, 2024
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets and Liabilities	Regulatory Assets and Liabilities. We apply the accounting guidance for regulated operations. Regulatory assets represent certain costs that are probable of recovery through future rates. We expect to recover such costs from our members in future revenues through rates under the wholesale power contracts we have with each of our members. The wholesale power contracts extend through December 31, 2085. Regulatory liabilities represent certain items of income that we are retaining and that will be applied in the future to reduce revenues required to be recovered from our members. The following regulatory assets and liabilities are reflected on the consolidated balance sheets as of March 31, 2024 and December 31, 2023. 2024 2023 (dollars in thousands) Regulatory Assets: Premium and loss on reacquired debt(a) $ 24,504 $ 25,476 Amortization of financing leases(b) 27,760 28,780 Outage costs(c) 34,627 30,040 Asset retirement obligations—Ashpond and other(l) 338,752 343,523 Depreciation expense - Plant Vogtle(d) 33,770 34,125 Depreciation expense - Plant Wansley(e) 330,945 335,884 Deferred charges related to Vogtle Units No. 3 and No. 4 training costs(f) 55,528 55,159 Interest rate options cost(g) 135,561 137,463 Deferral of effects on net margin—TA Smith Energy Facility(h) 129,299 130,786 Deferral of effects on net margin—BC Smith Energy Facility(p) 9,379 1,817 Other regulatory assets(o) 16,123 8,436 Total Regulatory Assets $ 1,136,248 $ 1,131,489 Regulatory Liabilities: Accumulated retirement costs for other obligations(i) $ 23,455 $ 25,992 Deferral of effects on net margin—Hawk Road Energy Facility(h) 15,866 16,020 Major maintenance reserve(j) 114,484 120,547 Deferred debt service adder(k) 174,507 170,466 Asset retirement obligations—Nuclear(l) 82,606 47,217 Revenue deferral plan(m) 279,467 308,507 Natural gas hedges(n) 10,381 13,445 Other regulatory liabilities(o) 3,318 4,126 Total Regulatory Liabilities $ 704,084 $ 706,320 Net Regulatory Assets $ 432,164 $ 425,169 (a) Represents premiums paid, together with unamortized transaction costs related to reacquired debt that are being amortized over the lives of the refunding debt, which range up to 20 years. (b) Represents the difference between expense recognized for rate-making purposes versus financial statement purposes related to finance lease payments and the aggregate of the amortization of the asset and interest on the obligation. (c) Consists of both coal-fired maintenance and nuclear refueling outage costs. Coal-fired outage costs are amortized on a straight-line basis to expense over periods up to 60 months, depending on the operating cycle of each unit. Nuclear refueling outage costs are amortized on a straight-line basis to expense over the 18 or 24-month operating cycles of each unit. (d) Prior to Nuclear Regulatory Commission (NRC) approval of a 20-year license extension for Plant Vogtle, we deferred the difference between Plant Vogtle depreciation expense based on the then 40-year operating license and depreciation expense assuming an expected 20-year license extension. Amortization commenced upon NRC approval of the license extension in 2009 and is being amortized over the remaining life of the plant. (e) Represents the deferral of accelerated depreciation associated with the early retirement of Plant Wansley, which occurred on August 31, 2022. Amortization commenced upon the retirement of Plant Wansley and will end no later than December 31, 2040. (f) Deferred charges consist of training related costs, including interest and carrying costs of such training. Amortization commences effective with the commercial operation date of each unit and is amortized to expense over the life of the units. (g) Deferral of premiums paid to purchase interest rate options used to hedge interest rates on certain borrowings, related carrying costs and other incidentals associated with construction of Vogtle Units No. 3 and No. 4. Amortization commenced in August 2023 after Vogtle Unit No. 3 was placed in service. (h) Effects on net margin for TA Smith and Hawk Road Energy Facilities were deferred through the end of 2015 and are being amortized over the remaining life of each respective plant. (i) Represents the accrual of retirement costs associated with long-lived assets for which there are no legal obligations to retire the assets. (j) Represents collections for future major maintenance costs; revenues are recognized as major maintenance costs are incurred. (k) Represents collections to fund certain debt payments to be made through the end of 2025 which will be in excess of amounts collected through depreciation expense; the deferred credits will be amortized over the remaining useful life of the plants. (l) Represents the difference in the timing of recognition of decommissioning costs for financial statement purposes versus ratemaking purposes, as well as the deferral of unrealized gains and losses of funds set aside for decommissioning. (m) Deferred revenues under a rate management program that allowed for additional collections over a five-year period which began in 2018. These amounts are being amortized to income and applied to member billings, per each members' election, over the subsequent five-year period. (n) Represents the deferral of unrealized gains on natural gas contracts. (o) The amortization periods for other regulatory assets range up to 30 years and the amortization periods of other regulatory liabilities range up to 24 years. (p) Effects on net margin for the BC Smith Energy Facility that are being deferred until on or before January 2026 and will be amortized over the remaining life of the plant.

Member Power Bill Prepayments

Member Power Bill Prepayments	3 Months Ended
	Mar. 31, 2024
Member Power Bill Prepayments
Member Power Bill Prepayments	Member Power Bill Prepayments. We have a power bill prepayment program pursuant to which members can prepay their power bills from us at a discount based on our avoided cost of borrowing. The prepayments are credited against the participating members' power bills in the month(s) agreed upon in advance. The discounts are credited against the power bills and are recorded as a reduction to member revenues. The prepayments are being credited against members' power bills through December 2028, with the majority of the balance scheduled to be credited by the end of 2025.

Debt

Debt	3 Months Ended
	Mar. 31, 2024
Debt Disclosure [Abstract]
Debt	Debt. a) Department of Energy Loan Guarantee: Pursuant to the loan guarantee program established under Title XVII of the Energy Policy Act of 2005, we and the U.S. Department of Energy, acting by and through the Secretary of Energy, entered into a Loan Guarantee Agreement on February 20, 2014 pursuant to which the Department of Energy agreed to guarantee our obligations under a Note Purchase Agreement, dated as of February 20, 2014 (the Original Note Purchase Agreement), among us, the Federal Financing Bank and the Department of Energy and two future advance promissory notes, each dated February 20, 2014, made by us to the Federal Financing Bank in the aggregate amount of $3,057,069,461 (the Original FFB Notes and together with the Original Note Purchase Agreement, the Original FFB Documents). On March 22, 2019, we and the Department of Energy entered into an Amended and Restated Loan Guarantee Agreement (as amended, the Loan Guarantee Agreement) which increased the aggregate amount guaranteed by the Department of Energy to $4,676,749,167. We also entered into a Note Purchase Agreement dated as of March 22, 2019 (the Additional Note Purchase Agreement), among us, the Federal Financing Bank and the Department of Energy and a future advance promissory note, dated March 22, 2019, made by us to the Federal Financing Bank in the amount of $1,619,679,706 (the Additional FFB Note and together with the Additional Note Purchase Agreement, the Additional FFB Documents). Together, the Original FFB Documents and Additional FFB Documents provide for a term loan facility (the Facility) under which we borrowed a total of $4,633,028,088. We received our final advance under the Facility in December 2022. Interest is payable quarterly in arrears and principal payments on all advances under the FFB Notes began on February 20, 2020. As of March 31, 2024, we have repaid $486,220,945 of principal on the FFB Notes and the aggregate Department of Energy-guaranteed borrowings outstanding, including capitalized interest, totaled $4,146,807,143. The final maturity date is February 20, 2044. We may voluntarily prepay outstanding borrowings under the Facility. Under the FFB Documents, any prepayment will be subject to a make-whole premium or discount, as applicable. Any amounts prepaid may not be re-borrowed. Under the Loan Guarantee Agreement, we are obligated to reimburse the Department of Energy in the event it is required to make any payments to the Federal Financing Bank under its guarantee. Our payment obligations to the Federal Financing Bank under the FFB Notes and reimbursement obligations to the Department of Energy under its guarantee, but not our covenants to the Department of Energy under the Loan Guarantee Agreement, are secured equally and ratably with all of our other obligations issued under our first mortgage indenture. Under the Loan Guarantee Agreement, we are subject to customary borrower affirmative and negative covenants and events of default. In addition, we are subject to project-related reporting requirements and other project-specific covenants and events of default. b) Rural Utilities Service Guaranteed Loans: For the three-month period ended March 31, 2024, we received advances on Rural Utilities Service-guaranteed Federal Financing Bank loans totaling $6,067,000 for long-term financing of general and environmental improvements at existing plants.

Vogtle Units No. 3 and No. 4 Co

Vogtle Units No. 3 and No. 4 Construction Project	3 Months Ended
	Mar. 31, 2024
Vogtle Units No. 3 and No. 4 Construction Project
Vogtle Units No. 3 and No. 4 Construction Project	Vogtle Units No. 3 and No. 4 Construction Project. We, Georgia Power, the Municipal Electric Authority of Georgia (MEAG), and the City of Dalton, Georgia, acting by and through its Board of Water, Light and Sinking Fund Commissioners, doing business as Dalton Utilities (collectively, the Co-owners) are parties to an Ownership Participation Agreement that, along with other agreements, governs our participation in two additional nuclear units under construction at Plant Vogtle, Units No. 3 and No. 4. The Co-owners appointed Georgia Power to act as agent under this agreement. Pursuant to this agreement, Georgia Power has designated Southern Nuclear Operating Company, Inc. as its agent for licensing, engineering, procurement, contract management, construction and pre-operation services. On July 31, 2023, Georgia Power placed Unit No. 3 in service. On February 14, 2024, Unit No. 4 achieved self-sustaining nuclear fission, commonly referred to as initial criticality, and on March 1, 2024, the generator successfully synchronized to the power grid and generated electricity for the first time. Georgia Power placed Unit No. 4 in service on April 29, 2024. Our ownership interest and proportionate share of the cost to construct Vogtle Units No. 3 and No. 4 is 30%, representing approximately 660 megawatts. Our project budget, which includes capital costs and allowance for funds used during construction, is approximately $8.3 billion. As of March 31, 2024, our actual costs related to the new Vogtle units were approximately $8.2 billion, net of $1.1 billion we received from Toshiba Corporation under a Guarantee Settlement Agreement and approximately $404 million we received from Georgia Power. For additional information regarding our participation in Plant Vogtle Units No. 3 and No. 4, see Note 8 in our 2023 Form 10-K. Plant Vogtle Unit No. 3 and No. 4 Commercial Operations For the three months ended March 31, 2024, we sold Georgia Power $12.1 million of nuclear production tax credits and recognized the amount as a credit to the Production expense line item within our consolidated income statements. In 2023, we sold Georgia Power $21.7 million of nuclear production tax credits. No credits were generated or sold during the three months ended March 31, 2023.

Measurement of Credit Losses on

Measurement of Credit Losses on Financial Instruments	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Measurement of Credit Losses on Financial Instruments	Measurement of Credit Losses on Financial Instruments. The financial assets we hold that are subject to credit losses (Topic 326) are predominately accounts receivable and certain cash equivalents classified as held-to-maturity debt (e.g. commercial paper). Our receivables are generally due within thirty days or less with a significant portion related to billings to our members. See Note F for information regarding our member receivables. Commercial paper we invest in is rated as investment grade. Given our historical experience, the short duration lifetime of these financial assets and the short time horizon over which to consider expectations of future economic conditions, we have assessed that non-collection of the cost basis of these financial assets is remote and we have not recognized an allowance for credit losses.

Asset Retirement Obligations

Asset Retirement Obligations	3 Months Ended
	Mar. 31, 2024
Asset Retirement Obligation [Abstract]
Asset Retirement Obligations	Asset Retirement Obligations. On February 14, 2024, Plant Vogtle Unit No. 4's nuclear reactor achieved self-sustaining nuclear fission, commonly referred to as initial criticality. During the first quarter of 2024, we recognized new nuclear asset retirement obligations totaling $65.1 million. During the three months ended March 31, 2024, no change in cash flow estimates related to existing coal ash related asset retirement obligations was recorded. We expect to periodically receive more refined estimates from Georgia Power regarding closure costs and the timing of expenditures.

Plant Purchase Agreement

Plant Purchase Agreement	3 Months Ended
	Mar. 31, 2024
Business Combination and Asset Acquisition [Abstract]
Plant Purchase Agreement	Plant Purchase Agreement.

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Mar. 31, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Recently Issued or Adopted Ac_2

Recently Issued or Adopted Accounting Pronouncements (Policies)	3 Months Ended
	Mar. 31, 2024
Accounting Standards Update and Change in Accounting Principle [Abstract]
Recently Issued or Adopted Accounting Pronouncements	Recently Issued or Adopted Accounting Pronouncements. In November 2023, the Financial Accounting Standards Board (FASB) issued “Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures.” The amendments in this update are intended to improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant expenses. The amendments in this update require disclosures to include significant segment expenses that are regularly provided to the chief operating decision maker (CODM), a description of other segment items by reportable segment, and any additional measures of a segment's profit or loss used by the CODM when deciding how to allocate resources. The amendments in this update are also applicable to entities with only one reportable segment. The amendments in this update also require all annual disclosures currently required by Topic 280 to be included in interim periods. The new standard is effective for us for annual reporting periods beginning after December 15, 2023 and interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted and requires retrospective application to all prior periods presented in the financial statements. We are currently evaluating the future impact of this standard on our consolidated financial statements. In December 2023, the FASB amended "Income Taxes (Topic 740): Improvements to Income Tax Disclosures”. The amendments in this update requires additional disclosures related to the rate reconciliation, income taxes paid and other amendments intended to improve effectiveness and comparability. The amendments in this update are effective for us for annual periods beginning after December 15, 2024. Early adoption is permitted and should be applied on a prospective basis. Retrospective application is permitted. We are currently evaluating the future impact of this standard on our consolidated financial statements, however, we do not anticipate the impact will be significant.

Fair Value (Tables)

Fair Value (Tables)	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Schedule of assets and liabilities measured at fair value on a recurring basis	The tables below detail assets and liabilities measured at fair value on a recurring basis at March 31, 2024 and December 31, 2023. Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs March 31, 2024 (Level 1) (Level 2) (Level 3) (dollars in thousands) Nuclear decommissioning trust funds: Domestic equity $ 259,404 $ 259,404 $ — $ — International equity trust 141,293 — 141,293 — Corporate bonds and debt 64,861 — 64,772 89 US Treasury securities 42,814 42,814 — — Mortgage backed securities 56,607 — 56,607 — Domestic mutual funds 92,626 92,626 — — Municipal bonds 303 — 303 — Federal agency securities 8,231 — 8,231 — International mutual funds 2,449 — 2,449 — Non-US Gov't bonds & private placements 3,708 — 3,708 — Other 7,002 7,002 — — Long-term investments: International equity trust 46,098 — 46,098 — Corporate bonds and debt 14,949 — 14,949 — US Treasury securities 14,783 14,783 — — Mortgage backed securities 17,068 — 17,068 — Domestic mutual funds 387,897 387,897 — — Treasury STRIPS 226,643 — 226,643 — Non-US Gov't bonds & private placements 1,775 — 1,775 — Other 602 602 — — Short-term investments: Treasury STRIPS 135,341 — 135,341 — Natural gas swaps 10,381 — 10,381 — Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs December 31, 2023 (Level 1) (Level 2) (Level 3) (dollars in thousands) Nuclear decommissioning trust funds: Domestic equity $ 234,979 $ 234,979 $ — $ — International equity trust 134,911 — 134,911 — Corporate bonds and debt 67,986 — 67,900 86 US Treasury securities 43,917 43,917 — — Mortgage backed securities 58,763 — 58,763 — Domestic mutual funds 85,481 85,481 — — Municipal bonds 303 — 303 — Federal agency securities 7,256 — 7,256 — Non-US Gov't bonds & private placements 2,717 — 2,717 — International mutual funds 2,012 — 2,012 — Other 2,914 2,914 — — Long-term investments: International equity trust 43,202 — 43,202 — Corporate bonds and debt 14,151 — 14,151 — US Treasury securities 17,243 17,243 — — Mortgage backed securities 15,024 — 15,024 — Domestic mutual funds 378,387 378,387 — — Treasury STRIPS 220,765 — 220,765 — Non-US Gov't bonds & private placements 1,568 — 1,568 — Other 392 392 — — Short-term investments: Treasury STRIPS 143,931 — 143,931 — Natural gas swaps 13,445 — 13,445 —
Schedule of estimated fair values of long-term debt, including current maturities	The estimated fair values of our long-term debt, including current maturities at March 31, 2024 and December 31, 2023 were as follows: 2024 2023 Carrying Fair Carrying Fair (in thousands) Long-term debt $ 11,966,572 $ 10,233,768 $ 12,096,552 $ 10,638,749

Derivative Instruments (Tables)

Derivative Instruments (Tables)	3 Months Ended
	Mar. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of notional volume of natural gas derivatives that is expected to settle or mature each year	The following table reflects the notional volume of our natural gas derivatives as of March 31, 2024 that is expected to settle or mature each year: Year Natural Gas Swaps (MMBTUs) (in millions) 2024 29.4 2025 25.2 2026 20.9 2027 10.3 2028 0.5 Total 86.3
Schedule of fair value of derivative instruments and effect on consolidated balance sheets	The table below reflects the fair value of derivative instruments and their effect on our consolidated balance sheets at March 31, 2024 and December 31, 2023. Balance Sheet Location Fair Value 2024 2023 (dollars in thousands) Assets: Natural gas swaps Other deferred charges $ 23,698 $ 25,459 Liabilities: Natural gas swaps Other current liabilities $ 12,688 $ 10,370 Natural gas swaps Other deferred credits $ 629 $ 1,644
Schedule of the realized gains and (losses) on derivative instruments recognized in margin	The following table presents the gross realized gains and (losses) on derivative instruments recognized in net margins for the three months ended March 31, 2024 and 2023. Statement of Three Months Ended March 31, 2024 2023 (dollars in thousands) Natural gas swaps gains Fuel $ 41 $ 135 Natural gas swaps losses Fuel (8,452) (9,397) Total $ (8,411) $ (9,262)
Schedule of unrealized gains on derivative instruments deferred on the balance sheet	The following table presents the unrealized gains on derivative instruments deferred on the balance sheet at March 31, 2024 and December 31, 2023. Balance Sheet Location 2024 2023 (dollars in thousands) Natural gas swaps Regulatory liability $ 10,381 $ 13,445 Total $ 10,381 $ 13,445

Investment Securities (Tables)

Investment Securities (Tables)	3 Months Ended
	Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Summary of debt and equity securities	The following tables summarize debt and equity securities as of March 31, 2024 and December 31, 2023. Gross Unrealized (dollars in thousands) March 31, 2024 Cost Gains Losses Fair Equity $ 350,947 $ 292,940 $ (6,033) $ 637,854 Debt 903,715 2,574 (27,229) 879,060 Other 7,549 1 (10) 7,540 Total $ 1,262,211 $ 295,515 $ (33,272) $ 1,524,454 Gross Unrealized (dollars in thousands) December 31, 2023 Cost Gains Losses Fair Equity $ 344,669 $ 246,795 $ (5,549) $ 585,915 Debt 908,316 3,938 (25,181) 887,073 Other 2,889 61 (36) 2,914 Total $ 1,255,874 $ 250,794 $ (30,766) $ 1,475,902

Revenue Recognition (Tables)

Revenue Recognition (Tables)	3 Months Ended
	Mar. 31, 2024
Revenue from Contract with Customer [Abstract]
Schedule of sales to members and sales to non-members	Sales to members for the three months ended March 31, 2024 and 2023 were as follows: Three Months Ended (dollars in thousands) 2024 2023 Capacity revenues $ 355,718 $ 242,043 Energy revenues 179,652 145,610 Total $ 535,370 $ 387,653 Sales to non-members during the three months ended March 31, 2024 and 2023 were as follows: Three Months Ended (dollars in thousands) 2024 2023 Energy revenues $ 158 $ 1,037 Capacity revenues 786 763 Total $ 944 $ 1,800

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2024
Leases [Abstract]
Schedule of balance sheet impact of leases	We combine lease and nonlease components for all lease agreements. Classification March 31, 2024 December 31, 2023 (dollars in thousands) Right-of-use assets—Finance leases Right-of-use assets $ 302,732 $ 302,732 Less: Accumulated provision for depreciation (279,465) (278,586) Total finance lease assets $ 23,267 $ 24,146 Lease liabilities—Finance leases Obligations under finance leases $ 43,586 $ 43,586 Long-term debt and finance leases due within one year 9,351 9,351 Total finance lease liabilities $ 52,937 $ 52,937 Classification March 31, 2024 December 31, 2023 (dollars in thousands) Right-of-use assets—Operating leases Electric plant in service, net $ 6,181 $ 6,587 Total operating lease assets $ 6,181 $ 6,587 Lease liabilities—Operating leases Capitalization—Other $ 4,786 $ 5,152 Other current liabilities 1,395 1,529 Total operating lease liabilities $ 6,181 $ 6,681
Schedule of lease cost	Three months ended Lease Cost Classification March 31, 2024 March 31, 2023 (dollars in thousands) Finance lease cost: Amortization of leased assets Depreciation and amortization $ 2,338 $ 2,099 Interest on lease liabilities Interest expense 1,400 1,638 Operating lease cost: Inventory (1) & production expense 538 329 Total leased cost $ 4,276 $ 4,066 (1) The majority of our operating lease costs relate to our railcar leases and such costs are added to the cost of our fossil-fuel inventories and are recognized in fuel expense as the inventories are consumed.
Summary of lease terms and discount rates	March 31, 2024 December 31, 2023 Lease Term and Discount Rate: Weighted-average remaining lease term (in years) Finance leases 5.01 5.26 Operating leases 5.70 5.77 Weighted-average discount rate: Finance leases 11.05 % 11.05 % Operating leases 6.45 % 6.37 %
Schedule of cash paid for amounts included in the measurement of lease liabilities	Three months ended March 31, 2024 2023 (dollars in thousands) Other Information: Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating leases $ 632 $ 409 Right-of-use assets obtained in exchange for new operating lease liabilities $ 17 $ —
Schedule of maturities of finance lease liabilities	Maturity analysis of our finance and operating lease liabilities as of March 31, 2024 is as follows: (dollars in thousands) Year Ending December 31, Finance Leases Operating Leases Total 2024 $ 14,949 $ 1,334 $ 16,283 2025 14,949 1,708 16,657 2026 14,949 1,416 16,365 2027 14,949 1,139 16,088 2028 3,052 1,029 4,081 Thereafter 7,633 723 8,356 Total lease payments $ 70,481 $ 7,349 $ 77,830 Less: imputed interest (17,544) (1,168) (18,712) Present value of lease liabilities $ 52,937 $ 6,181 $ 59,118
Schedule of maturities of operating lease liabilities	Maturity analysis of our finance and operating lease liabilities as of March 31, 2024 is as follows: (dollars in thousands) Year Ending December 31, Finance Leases Operating Leases Total 2024 $ 14,949 $ 1,334 $ 16,283 2025 14,949 1,708 16,657 2026 14,949 1,416 16,365 2027 14,949 1,139 16,088 2028 3,052 1,029 4,081 Thereafter 7,633 723 8,356 Total lease payments $ 70,481 $ 7,349 $ 77,830 Less: imputed interest (17,544) (1,168) (18,712) Present value of lease liabilities $ 52,937 $ 6,181 $ 59,118
Schedule of lease income	Lease income recognized during the three months ended March 31, 2024 and 2023 was as follows: Three Months Ended March 31, 2024 2023 (dollars in thousands) Lease income $ 1,387 $ 1,685

Restricted Cash and Investmen_2

Restricted Cash and Investments (Tables)	3 Months Ended
	Mar. 31, 2024
Restricted Investments Note [Abstract]
Reconciliation of cash, cash equivalents and restricted cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the unaudited consolidated balance sheets that sum to the total of the same such amounts reported in the unaudited consolidated statements of cash flows. Classification Three months ended March 31, 2024 March 31, 2023 (dollars in thousands) Cash and cash equivalents $ 327,470 $ 390,821 Restricted cash included in restricted cash and short-term investments — 16,000 Total cash, cash equivalents and restricted cash reported in the consolidated statements of cash flows $ 327,470 $ 406,821

Regulatory Assets and Liabili_2

Regulatory Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 2024
Regulatory Assets and Liabilities Disclosure [Abstract]
Schedule of regulatory assets and liabilities	The following regulatory assets and liabilities are reflected on the consolidated balance sheets as of March 31, 2024 and December 31, 2023. 2024 2023 (dollars in thousands) Regulatory Assets: Premium and loss on reacquired debt(a) $ 24,504 $ 25,476 Amortization of financing leases(b) 27,760 28,780 Outage costs(c) 34,627 30,040 Asset retirement obligations—Ashpond and other(l) 338,752 343,523 Depreciation expense - Plant Vogtle(d) 33,770 34,125 Depreciation expense - Plant Wansley(e) 330,945 335,884 Deferred charges related to Vogtle Units No. 3 and No. 4 training costs(f) 55,528 55,159 Interest rate options cost(g) 135,561 137,463 Deferral of effects on net margin—TA Smith Energy Facility(h) 129,299 130,786 Deferral of effects on net margin—BC Smith Energy Facility(p) 9,379 1,817 Other regulatory assets(o) 16,123 8,436 Total Regulatory Assets $ 1,136,248 $ 1,131,489 Regulatory Liabilities: Accumulated retirement costs for other obligations(i) $ 23,455 $ 25,992 Deferral of effects on net margin—Hawk Road Energy Facility(h) 15,866 16,020 Major maintenance reserve(j) 114,484 120,547 Deferred debt service adder(k) 174,507 170,466 Asset retirement obligations—Nuclear(l) 82,606 47,217 Revenue deferral plan(m) 279,467 308,507 Natural gas hedges(n) 10,381 13,445 Other regulatory liabilities(o) 3,318 4,126 Total Regulatory Liabilities $ 704,084 $ 706,320 Net Regulatory Assets $ 432,164 $ 425,169 (a) Represents premiums paid, together with unamortized transaction costs related to reacquired debt that are being amortized over the lives of the refunding debt, which range up to 20 years. (b) Represents the difference between expense recognized for rate-making purposes versus financial statement purposes related to finance lease payments and the aggregate of the amortization of the asset and interest on the obligation. (c) Consists of both coal-fired maintenance and nuclear refueling outage costs. Coal-fired outage costs are amortized on a straight-line basis to expense over periods up to 60 months, depending on the operating cycle of each unit. Nuclear refueling outage costs are amortized on a straight-line basis to expense over the 18 or 24-month operating cycles of each unit. (d) Prior to Nuclear Regulatory Commission (NRC) approval of a 20-year license extension for Plant Vogtle, we deferred the difference between Plant Vogtle depreciation expense based on the then 40-year operating license and depreciation expense assuming an expected 20-year license extension. Amortization commenced upon NRC approval of the license extension in 2009 and is being amortized over the remaining life of the plant. (e) Represents the deferral of accelerated depreciation associated with the early retirement of Plant Wansley, which occurred on August 31, 2022. Amortization commenced upon the retirement of Plant Wansley and will end no later than December 31, 2040. (f) Deferred charges consist of training related costs, including interest and carrying costs of such training. Amortization commences effective with the commercial operation date of each unit and is amortized to expense over the life of the units. (g) Deferral of premiums paid to purchase interest rate options used to hedge interest rates on certain borrowings, related carrying costs and other incidentals associated with construction of Vogtle Units No. 3 and No. 4. Amortization commenced in August 2023 after Vogtle Unit No. 3 was placed in service. (h) Effects on net margin for TA Smith and Hawk Road Energy Facilities were deferred through the end of 2015 and are being amortized over the remaining life of each respective plant. (i) Represents the accrual of retirement costs associated with long-lived assets for which there are no legal obligations to retire the assets. (j) Represents collections for future major maintenance costs; revenues are recognized as major maintenance costs are incurred. (k) Represents collections to fund certain debt payments to be made through the end of 2025 which will be in excess of amounts collected through depreciation expense; the deferred credits will be amortized over the remaining useful life of the plants. (l) Represents the difference in the timing of recognition of decommissioning costs for financial statement purposes versus ratemaking purposes, as well as the deferral of unrealized gains and losses of funds set aside for decommissioning. (m) Deferred revenues under a rate management program that allowed for additional collections over a five-year period which began in 2018. These amounts are being amortized to income and applied to member billings, per each members' election, over the subsequent five-year period. (n) Represents the deferral of unrealized gains on natural gas contracts. (o) The amortization periods for other regulatory assets range up to 30 years and the amortization periods of other regulatory liabilities range up to 24 years. (p) Effects on net margin for the BC Smith Energy Facility that are being deferred until on or before January 2026 and will be amortized over the remaining life of the plant.

General (Details)

General (Details)	3 Months Ended
	Mar. 31, 2024 member
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of electric distribution cooperative members	38

Fair Value - Asset and liabilit

Fair Value - Asset and liabilities measured at fair value on a recurring basis (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Fair value
Nuclear decommissioning trust fund	$ 679,298,000	$ 641,239,000
Long-term investments	709,815,000	690,732,000
Short-term investments	135,341,000	143,931,000
International equity trust
Fair value
Unfunded commitments	$ 0
Redemption notice period	3 days
Recurring basis | Natural gas swaps
Fair value
Derivative liabilities	$ 10,381,000	13,445,000
Recurring basis | Domestic equity
Fair value
Nuclear decommissioning trust fund	259,404,000	234,979,000
Recurring basis | International equity trust
Fair value
Nuclear decommissioning trust fund	141,293,000	134,911,000
Long-term investments	46,098,000	43,202,000
Recurring basis | Corporate bonds and debt
Fair value
Nuclear decommissioning trust fund	64,861,000	67,986,000
Long-term investments	14,949,000	14,151,000
Recurring basis | US Treasury securities
Fair value
Nuclear decommissioning trust fund	42,814,000	43,917,000
Long-term investments	14,783,000	17,243,000
Recurring basis | Mortgage backed securities
Fair value
Nuclear decommissioning trust fund	56,607,000	58,763,000
Long-term investments	17,068,000	15,024,000
Recurring basis | Domestic mutual funds
Fair value
Nuclear decommissioning trust fund	92,626,000	85,481,000
Long-term investments	387,897,000	378,387,000
Recurring basis | Municipal bonds
Fair value
Nuclear decommissioning trust fund	303,000	303,000
Recurring basis | Federal agency securities
Fair value
Nuclear decommissioning trust fund	8,231,000	7,256,000
Recurring basis | Treasury STRIPS
Fair value
Long-term investments	226,643,000	220,765,000
Short-term investments	135,341,000	143,931,000
Recurring basis | International mutual funds
Fair value
Nuclear decommissioning trust fund	2,449,000	2,012,000
Recurring basis | Non-US Gov't bonds & private placements
Fair value
Nuclear decommissioning trust fund	3,708,000	2,717,000
Long-term investments	1,775,000	1,568,000
Recurring basis | Other
Fair value
Nuclear decommissioning trust fund	7,002,000	2,914,000
Long-term investments	602,000	392,000
Recurring basis | (Level 1) | Natural gas swaps
Fair value
Derivative liabilities	0	0
Recurring basis | (Level 1) | Domestic equity
Fair value
Nuclear decommissioning trust fund	259,404,000	234,979,000
Recurring basis | (Level 1) | International equity trust
Fair value
Nuclear decommissioning trust fund	0	0
Long-term investments	0	0
Recurring basis | (Level 1) | Corporate bonds and debt
Fair value
Nuclear decommissioning trust fund	0	0
Long-term investments	0	0
Recurring basis | (Level 1) | US Treasury securities
Fair value
Nuclear decommissioning trust fund	42,814,000	43,917,000
Long-term investments	14,783,000	17,243,000
Recurring basis | (Level 1) | Mortgage backed securities
Fair value
Nuclear decommissioning trust fund	0	0
Long-term investments	0	0
Recurring basis | (Level 1) | Domestic mutual funds
Fair value
Nuclear decommissioning trust fund	92,626,000	85,481,000
Long-term investments	387,897,000	378,387,000
Recurring basis | (Level 1) | Municipal bonds
Fair value
Nuclear decommissioning trust fund	0	0
Recurring basis | (Level 1) | Federal agency securities
Fair value
Nuclear decommissioning trust fund	0	0
Recurring basis | (Level 1) | Treasury STRIPS
Fair value
Long-term investments	0	0
Short-term investments	0	0
Recurring basis | (Level 1) | International mutual funds
Fair value
Nuclear decommissioning trust fund	0	0
Recurring basis | (Level 1) | Non-US Gov't bonds & private placements
Fair value
Nuclear decommissioning trust fund	0	0
Long-term investments	0	0
Recurring basis | (Level 1) | Other
Fair value
Nuclear decommissioning trust fund	7,002,000	2,914,000
Long-term investments	602,000	392,000
Recurring basis | (Level 2) | Natural gas swaps
Fair value
Derivative liabilities	10,381,000	13,445,000
Recurring basis | (Level 2) | Domestic equity
Fair value
Nuclear decommissioning trust fund	0	0
Recurring basis | (Level 2) | International equity trust
Fair value
Nuclear decommissioning trust fund	141,293,000	134,911,000
Long-term investments	46,098,000	43,202,000
Recurring basis | (Level 2) | Corporate bonds and debt
Fair value
Nuclear decommissioning trust fund	64,772,000	67,900,000
Long-term investments	14,949,000	14,151,000
Recurring basis | (Level 2) | US Treasury securities
Fair value
Nuclear decommissioning trust fund	0	0
Long-term investments	0	0
Recurring basis | (Level 2) | Mortgage backed securities
Fair value
Nuclear decommissioning trust fund	56,607,000	58,763,000
Long-term investments	17,068,000	15,024,000
Recurring basis | (Level 2) | Domestic mutual funds
Fair value
Nuclear decommissioning trust fund	0	0
Long-term investments	0	0
Recurring basis | (Level 2) | Municipal bonds
Fair value
Nuclear decommissioning trust fund	303,000	303,000
Recurring basis | (Level 2) | Federal agency securities
Fair value
Nuclear decommissioning trust fund	8,231,000	7,256,000
Recurring basis | (Level 2) | Treasury STRIPS
Fair value
Long-term investments	226,643,000	220,765,000
Short-term investments	135,341,000	143,931,000
Recurring basis | (Level 2) | International mutual funds
Fair value
Nuclear decommissioning trust fund	2,449,000	2,012,000
Recurring basis | (Level 2) | Non-US Gov't bonds & private placements
Fair value
Nuclear decommissioning trust fund	3,708,000	2,717,000
Long-term investments	1,775,000	1,568,000
Recurring basis | (Level 2) | Other
Fair value
Nuclear decommissioning trust fund	0	0
Long-term investments	0	0
Recurring basis | (Level 3) | Natural gas swaps
Fair value
Derivative liabilities	0	0
Recurring basis | (Level 3) | Domestic equity
Fair value
Nuclear decommissioning trust fund	0	0
Recurring basis | (Level 3) | International equity trust
Fair value
Nuclear decommissioning trust fund	0	0
Long-term investments	0	0
Recurring basis | (Level 3) | Corporate bonds and debt
Fair value
Nuclear decommissioning trust fund	89,000	86,000
Long-term investments	0	0
Recurring basis | (Level 3) | US Treasury securities
Fair value
Nuclear decommissioning trust fund	0	0
Long-term investments	0	0
Recurring basis | (Level 3) | Mortgage backed securities
Fair value
Nuclear decommissioning trust fund	0	0
Long-term investments	0	0
Recurring basis | (Level 3) | Domestic mutual funds
Fair value
Nuclear decommissioning trust fund	0	0
Long-term investments	0	0
Recurring basis | (Level 3) | Municipal bonds
Fair value
Nuclear decommissioning trust fund	0	0
Recurring basis | (Level 3) | Federal agency securities
Fair value
Nuclear decommissioning trust fund	0	0
Recurring basis | (Level 3) | Treasury STRIPS
Fair value
Long-term investments	0	0
Short-term investments	0	0
Recurring basis | (Level 3) | International mutual funds
Fair value
Nuclear decommissioning trust fund	0	0
Recurring basis | (Level 3) | Non-US Gov't bonds & private placements
Fair value
Nuclear decommissioning trust fund	0	0
Long-term investments	0	0
Recurring basis | (Level 3) | Other
Fair value
Nuclear decommissioning trust fund	0	0
Long-term investments	$ 0	$ 0

Fair Value - Estimated fair val

Fair Value - Estimated fair value of long-term debt (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Carrying Value
Fair Value
Long-term debt	$ 11,966,572	$ 12,096,552
Fair Value | (Level 2)
Fair Value
Long-term debt	$ 10,233,768	$ 10,638,749

Derivative Instruments - Natura

Derivative Instruments - Natural gas derivatives (Details) - Natural gas swaps $ in Thousands, MMBTU in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) MMBTU	Dec. 31, 2023 USD ($)
Derivative Instruments
Derivative asset | $	$ 23,698	$ 25,459
Notional volume of natural gas derivatives (in MMBTUs)	86.3
2024
Derivative Instruments
Notional volume of natural gas derivatives (in MMBTUs)	29.4
2025
Derivative Instruments
Notional volume of natural gas derivatives (in MMBTUs)	25.2
2026
Derivative Instruments
Notional volume of natural gas derivatives (in MMBTUs)	20.9
2027
Derivative Instruments
Notional volume of natural gas derivatives (in MMBTUs)	10.3
2028
Derivative Instruments
Notional volume of natural gas derivatives (in MMBTUs)	0.5

Derivative Instruments - Fair v

Derivative Instruments - Fair value of derivative instruments (Details) - Natural gas swaps - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Assets:
Fair value of assets	$ 23,698,000	$ 25,459,000
Derivatives From Counterparties
Assets:
Fair value of assets	10,381,000	13,445,000
Other current liabilities
Liabilities:
Fair value of liabilities	12,688,000	10,370,000
Other deferred credits
Liabilities:
Fair value of liabilities	$ 629,000	$ 1,644,000

Derivative Instruments - Realiz

Derivative Instruments - Realized and unrealized gains (losses) on derivative instruments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Jun. 30, 2023
Gains and (losses) on derivative instruments
Net unrealized gains on derivative instruments	$ 10,381		$ 13,445
Natural gas swaps
Gains and (losses) on derivative instruments
Gains	41	$ 135
Losses	(8,452)	(9,397)
Total	(8,411)	$ (9,262)
Natural gas swaps | Regulatory liability
Gains and (losses) on derivative instruments
Net unrealized gains on derivative instruments	$ 10,381		$ 13,445

Investment Securities - Investm

Investment Securities - Investments in Debt and Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Cost
Equity	$ 350,947	$ 344,669
Debt	903,715	908,316
Other	7,549	2,889
Total	1,262,211	1,255,874
Gains
Equity	292,940	246,795
Debt	2,574	3,938
Other	1	61
Total	295,515	250,794
Losses
Equity	(6,033)	(5,549)
Debt	(27,229)	(25,181)
Other	(10)	(36)
Total	(33,272)	(30,766)
Fair Value
Equity	637,854	585,915
Debt	879,060	887,073
Other	7,540	2,914
Total	$ 1,524,454	$ 1,475,902

Investment Securities - Narrati

Investment Securities - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Amortized cost basis, unrealized loss positions	$ 832,901	$ 788,798
Unrealized loss position, less than 12 months	3,322	3,362
Unrealized loss position	27,229	25,181
Unrealized loss position, 12 months or longer	$ 23,907	$ 21,819

Revenue Recognition - Narrative

Revenue Recognition - Narrative (Details)	1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 31, 2022 unit	Mar. 31, 2024 USD ($) member service	Mar. 31, 2023 USD ($)	Dec. 31, 2018	Dec. 31, 2023 USD ($)
Revenue Recognition
Number of electric distribution cooperative members | member		38
Number of services provided | service		2
Margins for interest ratio		1.10
Targeted margins for interest ratio		1.14
Refund liability		$ 0			$ 34,266,000
Vogtle New Units
Revenue Recognition
Refund liability		279,467,000
Cumulative recovery of financing costs		369,102,000
Rate management program, additional collection period				5 years
Rate management program, billing period				5 years
Amounts billed under additional rate management program		30,409,000	$ 15,713,000
Vogtle Units No. 3 & No. 4
Revenue Recognition
Amounts billed under rate management program			$ 1,761,000
Cumulative recovery of financing costs		135,693,000
Washington County Power | Natural Gas Processing Plant
Revenue Recognition
Number of generating units acquired | unit	2
Sales to members
Revenue Recognition
Receivables from contracts		147,851,000			170,901,000
Sale of Bobby C. Smith Jr. Deferring Members' Output
Revenue Recognition
Receivables from contracts		$ 32,563,000			$ 30,883,000

Revenue Recognition - Sales to

Revenue Recognition - Sales to Members & Non-Members (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Revenue Recognition
Total operating revenues	$ 536,314	$ 389,453
Sales to members
Revenue Recognition
Total operating revenues	535,370	387,653
Sales to members | Capacity revenues
Revenue Recognition
Total operating revenues	355,718	242,043
Sales to members | Energy revenues
Revenue Recognition
Total operating revenues	179,652	145,610
Sales to non-members
Revenue Recognition
Total operating revenues	944	1,800
Sales to non-members | Capacity revenues
Revenue Recognition
Total operating revenues	786	763
Sales to non-members | Energy revenues
Revenue Recognition
Total operating revenues	$ 158	$ 1,037

Leases - Narrative (Details)

Leases - Narrative (Details)	3 Months Ended
	Mar. 31, 2024 lease option
Minimum
Leases
Finance lease renewal term	1 year
Maximum
Leases
Finance lease renewal term	5 years
Lease terms through December 31, 2027
Leases
Number of finance leases	3
Lease terms through June 30, 2031
Leases
Number of finance leases	1
Lease terms through February 2042
Leases
Number of renewal options | option	1
Operating lease, renewal term	20 years
Scherer Unit No. 2
Leases
Percentage of undivided interest in Scherer Unit No. 2	60%
Number of finance leases	4

Leases - Balance Sheet Impact (

Leases - Balance Sheet Impact (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Right-of-use assets—Finance leases
Right-of-use assets	$ 302,732	$ 302,732
Less: Accumulated provision for depreciation	(279,465)	(278,586)
Total finance lease assets	$ 23,267	$ 24,146
Finance lease, right-of-use asset, statement of financial position	Right-of-use assets—finance leases	Right-of-use assets—finance leases
Lease liabilities—Finance leases
Obligations under finance leases	$ 43,586	$ 43,586
Long-term debt and finance leases due within one year	9,351	9,351
Total finance lease liabilities	$ 52,937	$ 52,937
Finance lease, liability, current, statement of financial position	Long-term debt and finance leases due within one year	Long-term debt and finance leases due within one year
Right-of-use assets—Operating leases
Electric plant in service, net	$ 6,181	$ 6,587
Total operating lease assets	$ 6,181	$ 6,587
Operating lease, right-of-use asset, statement of financial position	In service	In service
Lease liabilities—Operating leases
Capitalization—Other	$ 4,786	$ 5,152
Other current liabilities	1,395	1,529
Total operating lease liabilities	$ 6,181	$ 6,681
Operating lease, liability, noncurrent, statement of financial position	Obligation under Hydro Facility Transactions	Obligation under Hydro Facility Transactions
Operating lease, liability, current, statement of financial position	Other current liabilities	Other current liabilities

Leases - Lease Cost (Details)

Leases - Lease Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Lease Cost
Amortization of leased assets	$ 2,338	$ 2,099
Interest on lease liabilities	1,400	1,638
Operating lease cost:	538	329
Total leased cost	$ 4,276	$ 4,066
Weighted-average remaining lease term (in years)
Finance leases	5 years 3 days		5 years 3 months 3 days
Operating leases	5 years 8 months 12 days		5 years 9 months 7 days
Weighted-average discount rate:
Finance leases	11.05%		11.05%
Operating leases	6.45%		6.37%

Leases - Other Lease Disclosure

Leases - Other Lease Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Lessee
Operating cash flows from operating leases	$ 632	$ 409
Right-of-use assets obtained in exchange for new operating lease liabilities	17	0
Finance Leases
2024	14,949
2025	14,949
2026	14,949
2027	14,949
2028	3,052
Thereafter	7,633
Total lease payments	70,481
Less: imputed interest	(17,544)
Total finance lease liabilities	52,937		$ 52,937
Operating Leases
2024	1,334
2025	1,708
2026	1,416
2027	1,139
2028	1,029
Thereafter	723
Total lease payments	7,349
Less: imputed interest	(1,168)
Total operating lease liabilities	6,181		$ 6,681
Total
2024	16,283
2025	16,657
2026	16,365
2027	16,088
2028	4,081
Thereafter	8,356
Total lease payments	77,830
Less: imputed interest	(18,712)
Present value of lease liabilities	59,118
Lessor
Lease income	$ 1,387	$ 1,685

Contingencies and Regulatory _2

Contingencies and Regulatory Matters (Details)					3 Months Ended	24 Months Ended
	May 12, 2023 complaint	Jan. 09, 2023 complaint	Feb. 07, 2022 complaint	Oct. 08, 2021 complaint	Mar. 31, 2024 plaintiff	Sep. 30, 2023 complaint
Contingencies and Regulatory Matters
Number of plaintiffs | plaintiff					44
New claims filed | complaint	8	1	4	3		8

Restricted Cash and Investmen_3

Restricted Cash and Investments - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Restricted Investments Note [Abstract]
Cash and cash equivalents	$ 327,470	$ 490,592	$ 390,821
Restricted cash included in restricted cash and short-term investments	0		16,000
Total cash, cash equivalents and restricted cash reported in the consolidated statements of cash flows	$ 327,470	$ 490,592	$ 406,821	$ 625,781

Regulatory Assets and Liabili_3

Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 1,136,248	$ 1,131,489
Total Regulatory Liabilities	704,084	706,320
Net Regulatory Assets	432,164	425,169
Accumulated retirement costs for other obligations
Regulatory Assets and Liabilities
Total Regulatory Liabilities	23,455	25,992
Deferral of effects on net margin - Hawk Road Energy Facility | Hawk Road Energy Facility
Regulatory Assets and Liabilities
Total Regulatory Liabilities	15,866	16,020
Major maintenance reserve
Regulatory Assets and Liabilities
Total Regulatory Liabilities	114,484	120,547
Deferred debt service adder
Regulatory Assets and Liabilities
Total Regulatory Liabilities	174,507	170,466
Asset retirement obligations
Regulatory Assets and Liabilities
Total Regulatory Liabilities	82,606	47,217
Revenue deferral plan
Regulatory Assets and Liabilities
Total Regulatory Liabilities	$ 279,467	308,507
Amortization period, regulatory liability	5 years
Natural gas hedges
Regulatory Assets and Liabilities
Total Regulatory Liabilities	$ 10,381	13,445
Other regulatory liabilities
Regulatory Assets and Liabilities
Total Regulatory Liabilities	$ 3,318	4,126
Other regulatory liabilities | Maximum
Regulatory Assets and Liabilities
Amortization period, regulatory liability	24 years
Premium and loss on reacquired debt
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 24,504	25,476
Premium and loss on reacquired debt | Maximum
Regulatory Assets and Liabilities
Amortization period, other regulatory assets	20 years
Amortization of financing leases
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 27,760	28,780
Outage costs
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 34,627	30,040
Coal-fired maintenance outage costs | Maximum
Regulatory Assets and Liabilities
Amortization period, other regulatory assets	60 months
Nuclear refueling outage costs | Minimum
Regulatory Assets and Liabilities
Amortization period, other regulatory assets	18 months
Nuclear refueling outage costs | Maximum
Regulatory Assets and Liabilities
Amortization period, other regulatory assets	24 months
Asset retirement obligations | Ashpond and other
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 338,752	343,523
Depreciation expense | Plant Vogtle
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 33,770	34,125
Operating license expected extension period for Plant Vogtle	20 years
Operating license period	40 years
Depreciation expense | Plant Wansley
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 330,945	335,884
Deferred charges related to Vogtle Units No. 3 and No. 4 training costs | Vogtle Units No. 3 & No. 4
Regulatory Assets and Liabilities
Total Regulatory Assets	55,528	55,159
Interest rate options cost
Regulatory Assets and Liabilities
Total Regulatory Assets	135,561	137,463
Deferral of effects on net margin - Smith Energy Facility | BC Smith Energy Facility
Regulatory Assets and Liabilities
Total Regulatory Assets	9,379	1,817
Deferral of effects on net margin - Smith Energy Facility | TA Smith Energy Facility
Regulatory Assets and Liabilities
Total Regulatory Assets	129,299	130,786
Other regulatory assets
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 16,123	$ 8,436
Other regulatory assets | Maximum
Regulatory Assets and Liabilities
Amortization period, other regulatory assets	30 years

Debt - Department of Energy Loa

Debt - Department of Energy Loan Guarantee (Details)	3 Months Ended
	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Mar. 22, 2019 USD ($)	Feb. 20, 2014 USD ($) note
Debt
Repayments of long-term debt	$ 136,047,000	$ 137,732,000
Long-term debt | Department of Energy guarantee
Debt
Aggregate borrowings including capitalized interest	4,146,807,143
Long-term debt | FFB
Debt
Number of future advance promissory notes | note				2
Maximum borrowing capacity			$ 1,619,679,706	$ 3,057,069,461
Maximum borrowing capacity designated for capitalized interest				$ 4,633,028,088
Repayments of long-term debt	$ 486,220,945
Long-term debt | FFB | Department of Energy guarantee | Services Agreement
Debt
Guarantee payment			$ 4,676,749,167

Debt - Rural Utilities Service

Debt - Rural Utilities Service Guaranteed Loans (Details) - Long-term debt - FFB - Rural Utilities Service Guaranteed Loans - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Apr. 30, 2024	Mar. 31, 2024
Debt
Advances received on loans		$ 6,067
Subsequent Event
Debt
Advances received on loans	$ 6,374

Vogtle Units No. 3 and No. 4 _2

Vogtle Units No. 3 and No. 4 Construction Project - Narrative (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2024 USD ($) unit MW	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)
Vogtle Units No. 3 & No. 4
Public Utility Property Plant and Equipment
Ownership interest (as a percent)	30%
Vogtle Units No. 3 & No. 4 | EPC Agreement | Westinghouse Electric Company LLC and Stone & Webster, Inc.
Public Utility Property Plant and Equipment
Number of nuclear units | unit	2
Vogtle Units No. 3 & No. 4 | Ownership participation agreement
Public Utility Property Plant and Equipment
Ownership share, generating capacity (in megawatts) | MW	660
Project budget	$ 8,300,000,000
Proceeds from settlement agreement	1,100,000,000
Total construction costs paid	8,200,000,000
Vogtle Units No. 3 & No. 4 | Global Amendments to Term Sheet | Jointly Owned Nuclear Power Plant | Georgia Power
Public Utility Property Plant and Equipment
Total construction costs paid	404,000,000
Vogtle Unit Number 3 | Georgia Power
Public Utility Property Plant and Equipment
Nuclear production tax credit	$ 12,100,000	$ 0	$ 21,700,000

Asset Retirement Obligations -

Asset Retirement Obligations - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Asset Retirement Obligation [Line Items]
Change in asset retirement obligations	$ 65,149	$ 87,509
Vogtle Unit Number 3
Asset Retirement Obligation [Line Items]
Cost to close plant	$ 65,100

Plant Purchase Agreement (Detai

Plant Purchase Agreement (Details) - Baconton Power - Natural Gas Processing Plant	Aug. 22, 2023 unit MW
Plant Acquisition [Line Items]
Number of generating units acquired | unit	3
Generating capacity of each nuclear unit (in megawatts) | MW	465