Fair Value Measurements - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
ASSETS
Cash equivalents		$ 14
Commodity contracts, assets		25,138	$ 132,229
Commodity contracts assets, other		(17,716)	(21,163)
Nuclear decommissioning trust:		1,162,397	1,073,410
Nuclear decommissioning trust, other		492,957	476,409
Other special use funds		351,998	347,231
Other special use funds, other		1,519	963
Total assets		1,539,547	1,552,870
Total assets, other		476,760	456,209
LIABILITIES
Gross derivative liability, other		11,445	15,357
Interest rate swaps		(99,137)	(42,446)
Total liabilities		(99,137)	(42,446)
Total liabilities, other		$ 11,445	15,357
Derivative Liability Statement Of Financial Position Extensible Enumeration Not Disclosed Flag	Subtotal risk management activities - derivative instruments	Subtotal risk management activities - derivative instruments
Commodity Option
ASSETS
Commodity contracts, assets		$ 24,729	132,098
Commodity contracts assets, other		(17,716)	(21,163)
LIABILITIES
Gross derivative liability, other		11,445	15,357
Interest rate swaps		(98,188)	(41,537)
Interest Rate Swap
ASSETS
Commodity contracts, assets		409	131
Commodity contracts assets, other		0	0
LIABILITIES
Gross derivative liability, other		0	0
Interest rate swaps		(949)	(909)
Equity securities
ASSETS
Nuclear decommissioning trust:		13,648	18,485
Nuclear decommissioning trust, other		(6,247)	3,827
Other special use funds		28,769	67,937
Other special use funds, other		1,519	963
U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust:		499,204	472,582
U.S. Treasury debt
ASSETS
Nuclear decommissioning trust:		248,897	211,923
Other special use funds		319,279	275,267
Corporate debt
ASSETS
Nuclear decommissioning trust:		167,372	149,226
Mortgage-backed securities
ASSETS
Nuclear decommissioning trust:		163,599	147,938
Municipal bonds
ASSETS
Nuclear decommissioning trust:		62,269	64,881
Other special use funds		3,950	4,027
Other fixed income
ASSETS
Nuclear decommissioning trust:		7,408	8,375
Level 1
ASSETS
Cash equivalents		14
Commodity contracts, assets		0	0
Nuclear decommissioning trust:		268,792	226,581
Other special use funds		346,529	342,241
Total assets		615,335	568,822
LIABILITIES
Gross derivative liability		0	0
Total liabilities		0	0
Level 1 | Commodity Option
ASSETS
Commodity contracts, assets			0
LIABILITIES
Gross derivative liability		0	0
Level 1 | Interest Rate Swap
ASSETS
Commodity contracts, assets		0	0
LIABILITIES
Gross derivative liability		0	0
Level 1 | Equity securities
ASSETS
Nuclear decommissioning trust:		19,895	14,658
Other special use funds		27,250	66,974
Level 1 | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust:		0	0
Level 1 | U.S. Treasury debt
ASSETS
Nuclear decommissioning trust:		248,897	211,923
Other special use funds		319,279	275,267
Level 1 | Corporate debt
ASSETS
Nuclear decommissioning trust:		0	0
Level 1 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trust:		0	0
Level 1 | Municipal bonds
ASSETS
Nuclear decommissioning trust:		0	0
Other special use funds		0	0
Level 1 | Other fixed income
ASSETS
Nuclear decommissioning trust:		0	0
Level 2
ASSETS
Cash equivalents		0
Commodity contracts, assets		29,101	127,260
Nuclear decommissioning trust:		400,648	370,420
Other special use funds		3,950	4,027
Total assets		433,699	501,707
LIABILITIES
Gross derivative liability		(95,550)	(26,783)
Total liabilities		(95,550)	(26,783)
Level 2 | Commodity Option
ASSETS
Commodity contracts, assets		28,692	127,129
LIABILITIES
Gross derivative liability		(94,601)	(25,874)
Level 2 | Interest Rate Swap
ASSETS
Commodity contracts, assets		409	131
LIABILITIES
Gross derivative liability		(949)	(909)
Level 2 | Equity securities
ASSETS
Nuclear decommissioning trust:		0	0
Other special use funds		0	0
Level 2 | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust:		0	0
Level 2 | U.S. Treasury debt
ASSETS
Nuclear decommissioning trust:		0	0
Other special use funds		0	0
Level 2 | Corporate debt
ASSETS
Nuclear decommissioning trust:		167,372	149,226
Level 2 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trust:		163,599	147,938
Level 2 | Municipal bonds
ASSETS
Nuclear decommissioning trust:		62,269	64,881
Other special use funds		3,950	4,027
Level 2 | Other fixed income
ASSETS
Nuclear decommissioning trust:		7,408	8,375
Level 3
ASSETS
Cash equivalents		0
Commodity contracts, assets		13,753	26,132
Nuclear decommissioning trust:		0	0
Other special use funds		0	0
Total assets		13,753	26,132
LIABILITIES
Gross derivative liability		(15,032)	(31,020)
Total liabilities		(15,032)	(31,020)
Level 3 | Commodity Option
ASSETS
Commodity contracts, assets		13,753	26,132
LIABILITIES
Gross derivative liability		(15,032)	(31,020)
Level 3 | Interest Rate Swap
ASSETS
Commodity contracts, assets		0	0
LIABILITIES
Gross derivative liability		0	0
Level 3 | Equity securities
ASSETS
Nuclear decommissioning trust:		0	0
Other special use funds		0	0
Level 3 | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust:		0	0
Level 3 | U.S. Treasury debt
ASSETS
Nuclear decommissioning trust:		0	0
Other special use funds		0	0
Level 3 | Corporate debt
ASSETS
Nuclear decommissioning trust:		0	0
Level 3 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trust:		0	0
Level 3 | Municipal bonds
ASSETS
Nuclear decommissioning trust:		0	0
Other special use funds		0	0
Level 3 | Other fixed income
ASSETS
Nuclear decommissioning trust:		0	0
Fair Value Measured at Net Asset Value Per Share | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust:		$ 499,204	$ 472,582