Fair Value Measurements - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
ASSETS
Cash equivalents	$ 14
Commodity contracts, assets	33,177	$ 132,229
Commodity contracts assets, other	(16,697)	(21,163)
Nuclear decommissioning trust:	1,125,617	1,073,410
Nuclear decommissioning trust, other	506,571	476,409
Other special use funds	352,877	347,231
Other special use funds, other	1,041	963
Total assets	1,511,685	1,552,870
Total assets, other	490,915	456,209
LIABILITIES
Gross derivative liability, other	10,643	15,357
Interest rate swaps	(99,257)	(42,446)
Total liabilities	(99,257)	(42,446)
Total liabilities, other	$ 10,643	$ 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
Equity securities
ASSETS
Nuclear decommissioning trust:	$ 8,530	$ 18,485
Nuclear decommissioning trust, other	(1,135)	3,827
Other special use funds	28,683	67,937
Other special use funds, other	1,041	963
U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust:	507,706	472,582
U.S. Treasury debt
ASSETS
Nuclear decommissioning trust:	231,003	211,923
Other special use funds	320,196	275,267
Corporate debt
ASSETS
Nuclear decommissioning trust:	149,541	149,226
Mortgage-backed securities
ASSETS
Nuclear decommissioning trust:	157,330	147,938
Municipal bonds
ASSETS
Nuclear decommissioning trust:	63,950	64,881
Other special use funds	3,998	4,027
Other fixed income
ASSETS
Nuclear decommissioning trust:	7,557	8,375
Commodity Option
ASSETS
Commodity contracts, assets	33,043	132,098
Commodity contracts assets, other	(16,697)	(21,163)
LIABILITIES
Gross derivative liability, other	10,643	15,357
Interest rate swaps	(97,559)	(41,537)
Interest Rate Swap
ASSETS
Commodity contracts, assets	134	131
Commodity contracts assets, other	0	0
LIABILITIES
Gross derivative liability, other	0	0
Interest rate swaps	(1,698)	(909)
Level 1
ASSETS
Cash equivalents	14
Commodity contracts, assets	0	0
Nuclear decommissioning trust:	240,668	226,581
Other special use funds	347,838	342,241
Total assets	588,520	568,822
LIABILITIES
Gross derivative liability	0	0
Total liabilities	0	0
Level 1 | Equity securities
ASSETS
Nuclear decommissioning trust:	9,665	14,658
Other special use funds	27,642	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:	231,003	211,923
Other special use funds	320,196	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 1 | Commodity Option
ASSETS
Commodity contracts, assets	0	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 2
ASSETS
Cash equivalents	0
Commodity contracts, assets	28,617	127,260
Nuclear decommissioning trust:	378,378	370,420
Other special use funds	3,998	4,027
Total assets	410,993	501,707
LIABILITIES
Gross derivative liability	(95,265)	(26,783)
Total liabilities	(95,265)	(26,783)
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:	149,541	149,226
Level 2 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trust:	157,330	147,938
Level 2 | Municipal bonds
ASSETS
Nuclear decommissioning trust:	63,950	64,881
Other special use funds	3,998	4,027
Level 2 | Other fixed income
ASSETS
Nuclear decommissioning trust:	7,557	8,375
Level 2 | Commodity Option
ASSETS
Commodity contracts, assets	28,483	127,129
LIABILITIES
Gross derivative liability	(93,567)	(25,874)
Level 2 | Interest Rate Swap
ASSETS
Commodity contracts, assets	134	131
LIABILITIES
Gross derivative liability	(1,698)	(909)
Level 3
ASSETS
Cash equivalents	0
Commodity contracts, assets	21,257	26,132
Nuclear decommissioning trust:	0	0
Other special use funds	0	0
Total assets	21,257	26,132
LIABILITIES
Gross derivative liability	(14,635)	(31,020)
Total liabilities	(14,635)	(31,020)
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
Level 3 | Commodity Option
ASSETS
Commodity contracts, assets	21,257	26,132
LIABILITIES
Gross derivative liability	(14,635)	(31,020)
Level 3 | Interest Rate Swap
ASSETS
Commodity contracts, assets	0	0
LIABILITIES
Gross derivative liability	0	0
Fair Value Measured at Net Asset Value Per Share | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust:	$ 507,706	$ 472,582