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Summary of significant accounting policies (Tables)
 12 Months Ended
Dec. 31, 2022
Accounting Policies [Abstract]  
Schedule of sales to members Sales to members were as follows:
(dollars in thousands)
202220212020
Capacity revenues$984,036 $946,662 $971,071 
Energy revenues990,647 610,447 405,939 
Total$1,974,683 $1,557,109 $1,377,010 
Sales to non-members were as follows:
(dollars in thousands)
202220212020
Energy revenues$155,372 $47,754 $608 
Capacity revenues82 — — 
Total$155,454 $47,754 $608 
Schedule of members whose revenues accounted for 10% or more of total operating revenues The following table reflects members whose revenues accounted for 10% or more of our total operating revenues in 2022, 2021 or 2020:
202220212020
Jackson EMC16.0 %15.2 %15.2 %
GreyStone Power Corporation, an EMC10.0 %8.7 %8.7 %
Cobb EMC9.5 %12.3 %13.2 %
Schedule of sales to non-members Sales to members were as follows:
(dollars in thousands)
202220212020
Capacity revenues$984,036 $946,662 $971,071 
Energy revenues990,647 610,447 405,939 
Total$1,974,683 $1,557,109 $1,377,010 
Sales to non-members were as follows:
(dollars in thousands)
202220212020
Energy revenues$155,372 $47,754 $608 
Capacity revenues82 — — 
Total$155,454 $47,754 $608 
Schedule reflecting details of asset retirement obligations included in the consolidated balance sheets
The following table reflects the details of the asset retirement obligations included in the consolidated balance sheets for the years 2022 and 2021.
(dollars in thousands)
NuclearCoal Ash PondOtherTotal
Balance at December 31, 2021$778,214 $442,686 $66,243 1,287,143 
Liabilities settled— (10,134)(184)(10,318)
Accretion41,892 12,196 1,865 55,953 
Deferred accretion— 479 — 479 
Change in cash flow estimates— 16,301 (5,815)10,486 
Balance at December 31, 2022$820,106 $461,528 $62,109 $1,343,743 
(dollars in thousands)
NuclearCoal Ash PondOtherTotal
Balance at December 31, 2020$738,217 $346,589 $51,177 $1,135,983 
Liabilities settled— (17,046)4,642 (12,404)
Accretion43,206 11,157 1,723 56,086 
Deferred accretion— (199)— (199)
Change in cash flow estimates(3,209)102,185 8,701 107,677 
Balance at December 31, 2021$778,214 $442,686 $66,243 $1,287,143 
Schedule of estimated costs of decommissioning of co-owned nuclear facilities Our portion of the estimated costs of decommissioning co-owned nuclear facilities are as follows:
(dollars in thousands)
2021 site studyHatch
Unit No. 1		Hatch
Unit No. 2		Vogtle
Unit No. 1		Vogtle
Unit No. 2
Expected start date of decommissioning2034203820472049
Estimated costs based on site study in 2021 dollars:
Radiated structures$227,000 $236,000 $200,000 $213,000 
Spent fuel management60,000 51,000 58,000 53,000 
Non-radiated structures15,000 21,000 24,000 31,000 
Total estimated site study costs$302,000 $308,000 $282,000 $297,000 
Schedule of external and internal trust funds by type of investment
The following table outlines the fair value of our nuclear decommissioning funds as of December 31, 2022 and December 31, 2021. The funds were invested in a diversified mix of approximately 69% equity and 31% fixed income securities in 2022 and 71% equity and 29% fixed income securities in 2021.
2022
External Trust Funds:(dollars in thousands)
Cost
12/31/2021		Purchases
Net Proceeds(1)
Unrealized Gain(Loss)Fair Value 12/31/2022
Equity$223,336 $9,255 $(3,655)$131,572 $360,508 
Debt204,935 191,958 (203,907)(12,869)180,117 
Other(795)3,287 (2,401)— 91 
$427,476 $204,500 $(209,963)$118,703 $540,716 
(1)Also included in net proceeds are net realized gains or losses, interest income, dividends and fees of $5,463,000.
2022
Internal Funds:(dollars in thousands)
Cost
12/31/2021		Purchases
Net
Proceeds(1)
Unrealized
Gain(Loss)		Fair Value
12/31/2022
Equity$68,914 $— $10,005 $18,995 $97,914 
Debt46,856 76,207 (79,828)(2,741)40,494 
$115,770 $76,207 $(69,823)$16,254 $138,408 
(1)Also included in net proceeds are net realized gains or losses, interest income, dividends, contributions and fees of $6,384,000.
2021
External Trust Funds:(dollars in thousands)
Cost
12/31/2020		Purchases
Net
Proceeds(1)
Unrealized
Gain(Loss)		Fair Value
12/31/2021
Equity$212,387 $50,309 $(39,360)$230,710 $454,046 
Debt196,810 583,003 (574,878)1,724 206,659 
Other17 41,841 (42,653)— (795)
$409,214 $675,153 $(656,891)$232,434 $659,910 
(1)Also included in net proceeds are net realized gains or losses, interest income, dividends and fees of $18,261,000.
2021
Internal Funds:(dollars in thousands)
Cost
12/31/2020		Purchases
Net
Proceeds(1)
Unrealized
Gain(Loss)		Fair Value
12/31/2021
Equity$50,647 $— $18,267 $44,735 $113,649 
Debt50,467 204,150 (207,761)181 47,037 
$101,114 $204,150 $(189,494)$44,916 $160,686 
(1)Also included in net proceeds are net realized gains or losses, interest income, dividends, contributions and fees of $14,656,000.
Schedule of annual depreciation rates Annual weighted average depreciation rates in effect in 2022, 2021, and 2020 were as follows:
Remaining Useful Life Range in
years*		202220212020
Steam production
20-22
13.77 %14.47 %2.58 %
Nuclear production
12-27
2.17 %2.18 %1.93 %
Hydro production
44
2.00 %2.00 %2.00 %
Other production
17-26
2.68 %2.60 %2.61 %
Transmission
12-27
2.75 %2.75 %2.75 %
General
1-43
2.00-33.33%
2.00-33.33%
2.00-33.33%
*Based on estimated retirement dates as of 2022. Actual retirement dates may be different. Remaining useful lives for nuclear production are based on the expiration date of the applicable operating license approved by the NRC.
Reconciliation of cash, cash equivalents and restricted cash The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets that sum to the total of the same such amounts reported in the consolidated statements of cash flows.
Classification
Twelve months ended
December 31, 2022December 31, 2021
(dollars in thousands)
 
Cash and cash equivalents$595,381 $579,350 
Restricted cash included in restricted cash and short-term investments30,400 1,800 
Total cash, cash equivalents and restricted cash reported in the consolidated statements of cash flows$625,781 $581,150 
Schedule of regulatory assets and liabilities 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 members.
(dollars in thousands)
20222021
Regulatory Assets:
Premium and loss on reacquired debt(a)$29,494 $33,200 
Amortization on financing leases(b)31,908 34,179 
Outage costs(c)29,317 31,956 
Asset retirement obligations –  Ashpond and other(l)353,212 335,231 
Asset retirement obligations – Nuclear(l)32,192 — 
Depreciation expense - Plant Vogtle(d)35,549 36,973 
Depreciation expense - Plant Wansley(e)361,784 204,891 
Deferred charges related to Vogtle Units No. 3 and No. 4 training costs(f)54,701 55,857 
Interest rate options cost(g)136,827 131,556 
Deferral of effects on net margin – Smith Energy Facility(h)136,730 142,675 
Other regulatory assets(o)10,591 2,272 
             Total Regulatory Assets$1,212,305 $1,008,790 
Regulatory Liabilities:
Accumulated retirement costs for other obligations(i)$35,580 $22,197 
Deferral of effects on net margin – Hawk Road Energy Facility(h)16,636 17,253 
Deferral of effects on net margin – Effingham Energy Facility(p)14,825 — 
Major maintenance reserve(j)74,584 73,059 
Amortization on financing leases(b)5,557 8,457 
Deferred debt service adder(k)154,514 138,897 
Asset retirement obligations – Nuclear(l)— 164,256 
Revenue deferral plan(m)357,460 359,799 
Natural gas hedges(n)131,804 63,994 
Other regulatory liabilities(o)1,230 1,537 
Total Regulatory Liabilities$792,190 $849,449 
Net regulatory assets$420,115 $159,341 
(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 21 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 will commence effective with the commercial operation date of each unit and 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 will commence the earlier of when Vogtle Unit No. 3 is placed in service or December 2023.
(h)Effects on net margin for 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 allows for additional collections over a five-year period beginning in 2018. These amounts will be amortized to income and applied to member billings, per each member's 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 27 years and the amortization periods of other regulatory liabilities range up to 4 years.
(p)Effects on net margin for the Effingham Energy Facility that are being deferred until on or before January 2026 and will be amortized over the remaining life of the plant.