Summary of significant accounting policies (Tables)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Schedule of sales to members

Sales to members were as follows:

	(dollars in thousands)
	2021		2020		2019
Capacity revenues	$	946,662	$	971,071	$	942,057
Energy revenues	610,447		405,939		487,795
Total	$	1,557,109	$	1,377,010	$	1,429,852

Sales to non-members were as follows:

	(dollars in thousands)
	2021		2020		2019
Energy revenues	$	47,754	$	608	$	440

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 2021, 2020 and 2019:

	2021		2020		2019
Jackson EMC	15.2	%	15.2	%	14.4	%
Cobb EMC	12.3	%	13.2	%	13.8	%

Schedule of sales to non-members

Sales to members were as follows:

	(dollars in thousands)
	2021		2020		2019
Capacity revenues	$	946,662	$	971,071	$	942,057
Energy revenues	610,447		405,939		487,795
Total	$	1,557,109	$	1,377,010	$	1,429,852

Sales to non-members were as follows:

	(dollars in thousands)
	2021		2020		2019
Energy revenues	$	47,754	$	608	$	440

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 2021 and 2020.

	(dollars in thousands)
	Nuclear		Coal Ash Pond		Other		Total
Balance at December 31, 2020	$	738,217	$	346,589	$	51,177	1,135,983
Liabilities settled	—		(17,046)		4,642		(12,404)
Accretion	43,206		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

	(dollars in thousands)
	Nuclear		Coal Ash Pond		Other		Total
Balance at December 31, 2019	$	697,441	$	329,264	$	43,935	$	1,070,640
Liabilities settled	—		(4,656)		(2,332)		(6,988)
Accretion	40,776		12,059		1,640		54,475
Deferred accretion	—		(853)		—		(853)
Change in cash flow estimates	—		10,775		7,934		18,709
Balance at December 31, 2020	$	738,217	$	346,589	$	51,177	$	1,135,983

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 study	Hatch Unit No. 1		Hatch Unit No. 2		Vogtle Unit No. 1		Vogtle Unit No. 2
Expected start date of decommissioning	2034		2038		2047		2049
Estimated costs based on site study in 2021 dollars:
Radiated structures	$	227,000	$	236,000	$	200,000	$	213,000
Spent fuel management	60,000		51,000		58,000		53,000
Non-radiated structures	15,000		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, 2021 and December 31, 2020. The funds were invested in a diversified mix of approximately 71% equity and 29% fixed income securities in 2021 and 64% equity and 36% fixed income securities in 2020.

	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
Debt	196,810		583,003		(574,878)		1,724		206,659
Other	17		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
Debt	50,467		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.

	2020
External Trust Funds:	(dollars in thousands)
	Cost 12/31/2019		Purchases		Net Proceeds(1)		Unrealized Gain(Loss)		Fair Value 12/31/2020
Equity	$	212,585	$	27,707	$	(16,444)	$	177,866	$	401,714
Debt	174,645		536,147		(523,926)		11,100		197,966
Other	(702)		14,756		(15,553)		—		(1,499)
	$	386,528	$	578,610	$	(555,923)	$	188,966	$	598,181

(1)Also included in net proceeds are net realized gains or losses, interest income, dividends and fees of $22,686,000.

	2020
Internal Funds:	(dollars in thousands)
	Cost 12/31/2019		Purchases		Net Proceeds(1)		Unrealized Gain(Loss)		Fair Value 12/31/2020
Equity	$	47,062	$	—	$	3,586	$	33,665	$	84,313
Debt	44,347		132,710		(126,590)		2,519		52,986
	$	91,409	$	132,710	$	(123,004)	$	36,184	$	137,299

(1)Also included in net proceeds are net realized gains or losses, interest income, dividends, contributions and fees of $9,705,000.

Schedule of annual depreciation rates

Annual weighted average depreciation rates in effect in 2021, 2020, and 2019 were as follows:

	Remaining Useful Life Range in years*	2021		2020		2019
Steam production	1-23	14.47	%	2.58	%	2.61	%
Nuclear production	13-28	2.18	%	1.93	%	1.94	%
Hydro production	45	2.00	%	2.00	%	2.00	%
Other production	18-27	2.60	%	2.61	%	2.61	%
Transmission	13-28	2.75	%	2.75	%	2.75	%
General	1-44	2.00-33.33%		2.00-33.33%		2.00-33.33%

*Based on estimated retirement dates as of 2021. 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, 2021		December 31, 2020
	(dollars in thousands)
Cash and cash equivalents	$	579,350	$	405,511
Restricted cash included in prepayments and other current assets	1,800		—
Total cash, cash equivalents and restricted cash reported in the consolidated statements of cash flows	$	581,150	$	405,511

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)
	2021		2020
Regulatory Assets:
Premium and loss on reacquired debt(a)	$	33,200	$	35,433
Amortization on financing leases(b)	34,179		35,328
Outage costs(c)	31,956		35,232
Asset retirement obligations –  Ashpond and other(k)	335,231		242,832
Depreciation expense - Plant Vogtle(d)	36,973		38,396
Depreciation expense - Plant Wansley(e)	204,891		—
Deferred charges related to Vogtle Units No. 3 and No. 4 training costs(f)	55,857		55,430
Interest rate options cost(g)	131,556		126,813
Deferral of effects on net margin – Smith Energy Facility(h)	142,675		148,620
Other regulatory assets(o)	2,272		13,354
Total Regulatory Assets	$	1,008,790	$	731,438
Regulatory Liabilities:
Accumulated retirement costs for other obligations(i)	$	22,197	$	20,054
Deferral of effects on net margin – Hawk Road Energy Facility(h)	17,253		17,869
Major maintenance reserve(j)	73,059		39,776
Amortization on financing leases(b)	8,457		11,356
Deferred debt service adder(k)	138,897		123,772
Asset retirement obligations – Nuclear(l)	164,256		130,901
Revenue deferral plan(m)	359,799		220,111
Natural gas hedges(n)	63,994		—
Other regulatory liabilities(m)	1,537		2,560
Total Regulatory Liabilities	$	849,449	$	566,399
Net regulatory assets	$	159,341	$	165,039

(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 22 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 is expected by the end of August 2022. Amortization will commence upon retirement of Plant Wansley and 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 when Vogtle Unit No. 3 is placed in service.

(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 over the subsequent five-year period.

(n)Represents the deferral of unrealized gains on natural gas hedges.

(o)The amortization periods for other regulatory assets range up to 28 years and the amortization periods of other regulatory liabilities range up to 5 years.