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Fair Value Measurements - Fair Value of Assets and Liabilities (Details) - USD ($) $ in Thousands | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Assets |  |
Commodity contracts, assets | $ 110,389 | $ 4,749
Commodity contracts, liabilities | (4,690) | (4,271)
Nuclear decommissioning trust | 1,294,757 | 1,138,435
Nuclear decommissioning trust, other | 567,266 | 592,227
Other special use fund | 358,410 | 254,509
Other special use funds, other | 936 | 504
Total assets | 1,763,556 | 1,397,693
Total assets, other | 563,512 | 588,460
Liabilities |  |
Derivative instruments, other | 3,105 | 2,986
Derivative instruments, total | (4,373) | (18,619)
Equity securities |  |
Assets |  |
Nuclear decommissioning trust | 17,482 | 11,968
Nuclear decommissioning trust, other | (27,782) | (17,828)
Other special use fund | 48,506 | 37,841
Other special use funds, other | 936 | 504
U.S. commingled equity funds |  |
Assets |  |
Nuclear decommissioning trust | 595,048 | 610,055
U.S. Treasury debt |  |
Assets |  |
Nuclear decommissioning trust | 240,745 | 164,514
Other special use fund | 298,170 | 203,220
Corporate debt |  |
Assets |  |
Nuclear decommissioning trust | 203,454 | 149,509
Mortgage-backed securities |  |
Assets |  |
Nuclear decommissioning trust | 155,574 | 99,623
Municipal bonds |  |
Assets |  |
Nuclear decommissioning trust | 72,189 | 89,705
Other special use fund | 11,734 | 13,448
Other fixed income |  |
Assets |  |
Nuclear decommissioning trust | 10,265 | 13,061
Level 1 |  |
Assets |  |
Commodity contracts, assets | 0 | 0
Nuclear decommissioning trust | 286,009 | 194,310
Other special use fund | 345,740 | 240,557
Total assets | 631,749 | 434,867
Liabilities |  |
Derivative instruments | 0 | 0
Level 1 | Equity securities |  |
Assets |  |
Nuclear decommissioning trust | 45,264 | 29,796
Other special use fund | 47,570 | 37,337
Level 1 | U.S. commingled equity funds |  |
Assets |  |
Nuclear decommissioning trust | 0 | 0
Level 1 | U.S. Treasury debt |  |
Assets |  |
Nuclear decommissioning trust | 240,745 | 164,514
Other special use fund | 298,170 | 203,220
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 | 115,079 | 9,016
Nuclear decommissioning trust | 441,482 | 351,898
Other special use fund | 11,734 | 13,448
Total assets | 568,295 | 374,362
Liabilities |  |
Derivative instruments | (4,740) | (20,498)
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 | 203,454 | 149,509
Level 2 | Mortgage-backed securities |  |
Assets |  |
Nuclear decommissioning trust | 155,574 | 99,623
Level 2 | Municipal bonds |  |
Assets |  |
Nuclear decommissioning trust | 72,189 | 89,705
Other special use fund | 11,734 | 13,448
Level 2 | Other fixed income |  |
Assets |  |
Nuclear decommissioning trust | 10,265 | 13,061
Level 3 |  |
Assets |  |
Commodity contracts, assets | 0 | 4
Nuclear decommissioning trust | 0 | 0
Other special use fund | 0 | 0
Total assets | 0 | 4
Liabilities |  |
Derivative instruments | (2,738) | (1,107)
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
NAV | U.S. commingled equity funds |  |
Assets |  |
Nuclear decommissioning trust | $ 595,048 | $ 610,055

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