Fair Value Measurements - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
ASSETS
Cash equivalents	$ 4,518	$ 10
Nuclear decommissioning trusts:	1,300,012	1,201,246
Nuclear decommissioning trust, other	414,905	408,849
Other special use funds	387,499	362,781
Other special use funds, other	1,760	2,196
Total assets	1,692,670	1,570,845
Total assets, other	414,814	409,356
Commodity contracts
ASSETS
Commodity contracts, assets	641	6,808
Commodity contracts assets, other	(1,851)	(1,689)
LIABILITIES
Gross derivative liability, other	(7,015)	4,823
Interest rate swaps	(108,532)	(123,888)
Equity securities
ASSETS
Nuclear decommissioning trusts:	18,528	10,297
Nuclear decommissioning trust, other	1,608	(767)
Other special use funds	55,736	43,187
Other special use funds, other	1,760	2,196
U.S. commingled equity funds
ASSETS
Nuclear decommissioning trusts:	413,297	409,616
U.S. Treasury debt
ASSETS
Nuclear decommissioning trusts:	366,093	319,734
Other special use funds	331,763	319,594
Corporate debt
ASSETS
Nuclear decommissioning trusts:	217,396	188,317
Mortgage-backed securities
ASSETS
Nuclear decommissioning trusts:	216,113	208,306
Municipal bonds
ASSETS
Nuclear decommissioning trusts:	41,634	59,323
Other fixed income
ASSETS
Nuclear decommissioning trusts:	26,951	5,653
Level 1
ASSETS
Cash equivalents	4,518	10
Nuclear decommissioning trusts:	383,013	330,798
Other special use funds	385,739	360,585
Total assets	773,270	691,393
Level 1 | Commodity contracts
ASSETS
Commodity contracts, assets	0	0
LIABILITIES
Gross derivative liability	0	0
Level 1 | Equity securities
ASSETS
Nuclear decommissioning trusts:	16,920	11,064
Other special use funds	53,976	40,991
Level 1 | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trusts:	0	0
Level 1 | U.S. Treasury debt
ASSETS
Nuclear decommissioning trusts:	366,093	319,734
Other special use funds	331,763	319,594
Level 1 | Corporate debt
ASSETS
Nuclear decommissioning trusts:	0	0
Level 1 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trusts:	0	0
Level 1 | Municipal bonds
ASSETS
Nuclear decommissioning trusts:	0	0
Level 1 | Other fixed income
ASSETS
Nuclear decommissioning trusts:	0	0
Level 2
ASSETS
Cash equivalents	0	0
Nuclear decommissioning trusts:	502,094	461,599
Other special use funds	0	0
Total assets	504,530	463,480
Level 2 | Commodity contracts
ASSETS
Commodity contracts, assets	2,436	1,881
LIABILITIES
Gross derivative liability	(83,373)	(127,016)
Level 2 | Equity securities
ASSETS
Nuclear decommissioning trusts:	0	0
Other special use funds	0	0
Level 2 | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trusts:	0	0
Level 2 | U.S. Treasury debt
ASSETS
Nuclear decommissioning trusts:	0	0
Other special use funds	0	0
Level 2 | Corporate debt
ASSETS
Nuclear decommissioning trusts:	217,396	188,317
Level 2 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trusts:	216,113	208,306
Level 2 | Municipal bonds
ASSETS
Nuclear decommissioning trusts:	41,634	59,323
Level 2 | Other fixed income
ASSETS
Nuclear decommissioning trusts:	26,951	5,653
Level 3
ASSETS
Cash equivalents	0	0
Nuclear decommissioning trusts:	0	0
Other special use funds	0	0
Total assets	56	6,616
Level 3 | Commodity contracts
ASSETS
Commodity contracts, assets	56	6,616
LIABILITIES
Gross derivative liability	(18,144)	(1,695)
Level 3 | Equity securities
ASSETS
Nuclear decommissioning trusts:	0	0
Other special use funds	0	0
Level 3 | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trusts:	0	0
Level 3 | U.S. Treasury debt
ASSETS
Nuclear decommissioning trusts:	0	0
Other special use funds	0	0
Level 3 | Corporate debt
ASSETS
Nuclear decommissioning trusts:	0	0
Level 3 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trusts:	0	0
Level 3 | Municipal bonds
ASSETS
Nuclear decommissioning trusts:	0	0
Level 3 | Other fixed income
ASSETS
Nuclear decommissioning trusts:	0	0
Fair Value Measured at Net Asset Value Per Share | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trusts:	$ 413,297	$ 409,616