Fair Value Measurements - Fair Value of Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
ASSETS
Commodity contracts, assets	$ 132,229
Commodity contracts, liabilities	(21,163)
Nuclear decommissioning trust	1,073,410	$ 1,294,757
Nuclear decommissioning trust, other	476,409	567,266
Other special use fund	347,231	358,410
Other special use funds, other	963	936
Total assets	1,552,870	1,763,556
Total assets, other	456,209	$ 563,512
LIABILITIES
Derivative instruments, other	15,357
Derivative instruments, total	(42,446)
Total liabilities	(42,446)
Total liabilities other	$ 15,357
DerivativeLiabilityStatementOfFinancialPositionExtensibleEnumerationNotDisclosedFlag	Subtotal risk management activities - derivative instruments	Subtotal risk management activities - derivative instruments
Commodity Contracts
ASSETS
Commodity contracts, assets	$ 153,261	$ 115,079
LIABILITIES
Derivative instruments	(56,893)	(7,478)
Derivative instruments, total	(41,537)	(4,373)
Commodity contracts
ASSETS
Commodity contracts, assets	132,098	110,389
Commodity contracts, liabilities	(21,163)	(4,690)
LIABILITIES
Derivative instruments, other	15,357	3,105
Derivative instruments, total	(41,537)	(4,373)
Interest rate swaps
ASSETS
Commodity contracts, assets	131
Commodity contracts, liabilities	0
LIABILITIES
Derivative instruments, other	0
Derivative instruments, total	(909)
Equity securities
ASSETS
Nuclear decommissioning trust	18,485	17,482
Nuclear decommissioning trust, other	3,827	(27,782)
Other special use fund	67,937	48,506
Other special use funds, other	963	936
U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust	472,582	595,048
U.S. Treasury debt
ASSETS
Nuclear decommissioning trust	211,923	240,745
Other special use fund	275,267	298,170
Corporate debt
ASSETS
Nuclear decommissioning trust	149,226	203,454
Mortgage-backed securities
ASSETS
Nuclear decommissioning trust	147,938	155,574
Municipal bonds
ASSETS
Nuclear decommissioning trust	64,881	72,189
Other special use fund	4,027	11,734
Other fixed income
ASSETS
Nuclear decommissioning trust	8,375	10,265
Level 1
ASSETS
Commodity contracts, assets	0
Nuclear decommissioning trust	226,581	286,009
Other special use fund	342,241	345,740
Total assets	568,822	631,749
LIABILITIES
Derivative instruments	0
Total liabilities	0
Level 1 | Commodity contracts
ASSETS
Commodity contracts, assets	0	0
LIABILITIES
Derivative instruments	0	0
Level 1 | Interest rate swaps
ASSETS
Commodity contracts, assets	0
LIABILITIES
Derivative instruments	0
Level 1 | Equity securities
ASSETS
Nuclear decommissioning trust	14,658	45,264
Other special use fund	66,974	47,570
Level 1 | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust	0	0
Level 1 | U.S. Treasury debt
ASSETS
Nuclear decommissioning trust	211,923	240,745
Other special use fund	275,267	298,170
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 fund	0	0
Level 1 | Other fixed income
ASSETS
Nuclear decommissioning trust	0	0
Level 2
ASSETS
Commodity contracts, assets	127,260
Nuclear decommissioning trust	370,420	441,482
Other special use fund	4,027	11,734
Total assets	501,707	568,295
LIABILITIES
Derivative instruments	(26,783)
Total liabilities	(26,783)
Level 2 | Commodity contracts
ASSETS
Commodity contracts, assets	127,129	115,079
LIABILITIES
Derivative instruments	(25,874)	(4,740)
Level 2 | Interest rate swaps
ASSETS
Commodity contracts, assets	131
LIABILITIES
Derivative instruments	(909)
Level 2 | Equity securities
ASSETS
Nuclear decommissioning trust	0	0
Other special use fund	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 fund	0	0
Level 2 | Corporate debt
ASSETS
Nuclear decommissioning trust	149,226	203,454
Level 2 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trust	147,938	155,574
Level 2 | Municipal bonds
ASSETS
Nuclear decommissioning trust	64,881	72,189
Other special use fund	4,027	11,734
Level 2 | Other fixed income
ASSETS
Nuclear decommissioning trust	8,375	10,265
Level 3
ASSETS
Commodity contracts, assets	26,132
Nuclear decommissioning trust	0	0
Other special use fund	0	0
Total assets	26,132	0
LIABILITIES
Derivative instruments	(31,020)
Total liabilities	(31,020)
Level 3 | Commodity contracts
ASSETS
Commodity contracts, assets	26,132	0
LIABILITIES
Derivative instruments	(31,020)	(2,738)
Level 3 | Interest rate swaps
ASSETS
Commodity contracts, assets	0
LIABILITIES
Derivative instruments	0
Level 3 | Equity securities
ASSETS
Nuclear decommissioning trust	0	0
Other special use fund	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 fund	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 fund	0	0
Level 3 | Other fixed income
ASSETS
Nuclear decommissioning trust	0	0
Level 3 | Forward Contracts | Commodity Contracts
ASSETS
Total assets	26,132	0
LIABILITIES
Total liabilities	(31,020)	(2,738)
Level 3 | Forward Contracts | Natural Gas: | Commodity Contracts | Discounted Cash Flows
ASSETS
Total assets	0	0
LIABILITIES
Total liabilities	(29,261)	(2,738)
NAV | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust	$ 472,582	$ 595,048