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Fair Value Measurements - Schedule of Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
ASSETS |  |
Cash equivalents | $ 1 | $ 23
Nuclear decommissioning trusts: | 1,393,446 | 1,282,845
Nuclear decommissioning trust, other | 489,772 | 426,404
Other special use funds: | 429,932 | 408,357
Other special use funds, other | 2,167 | 2,851
Total assets | 1,845,615 | 1,707,783
Total assets, other | 480,363 | 425,485
Commodity contracts |  |
ASSETS |  |
Commodity contracts | 22,236 | 16,558
Commodity contracts, other | (11,576) | (3,770)
LIABILITIES |  |
Derivative instruments, other | 5,785 | 817
Amounts Reported on Balance Sheets | (39,078) | (61,786)
Equity securities |  |
ASSETS |  |
Nuclear decommissioning trusts: | 21,241 | 15,736
Nuclear decommissioning trust, other | 2,091 | 3,335
Other special use funds: | 105,521 | 27,813
Other special use funds, other | 2,167 | 2,851
U.S. commingled equity funds |  |
ASSETS |  |
Nuclear decommissioning trusts: | 487,681 | 423,069
U.S. Treasury debt |  |
ASSETS |  |
Nuclear decommissioning trusts: | 352,998 | 367,396
Other special use funds: | 324,411 | 355,544
Corporate debt |  |
ASSETS |  |
Nuclear decommissioning trusts: | 237,191 | 203,180
Mortgage-backed securities |  |
ASSETS |  |
Nuclear decommissioning trusts: | 232,657 | 208,533
Municipal bonds |  |
ASSETS |  |
Nuclear decommissioning trusts: | 37,785 | 37,429
Other fixed income |  |
ASSETS |  |
Nuclear decommissioning trusts: | 23,893 | 27,502
Cash equivalents |  |
ASSETS |  |
Other special use funds: |  | 25,000
Other special use funds, other |  | 0
Level 1 |  |
ASSETS |  |
Cash equivalents | 1 | 23
Nuclear decommissioning trusts: | 372,148 | 379,255
Other special use funds: | 427,765 | 405,506
Total assets | 799,914 | 784,784
Level 1 | Pinnacle West Captive Insurance Cell |  |
ASSETS |  |
Other special use funds: | 39,400 | 34,200
Level 1 | Commodity contracts |  |
ASSETS |  |
Commodity contracts | 0 | 0
LIABILITIES |  |
Derivative instruments | 0 | 0
Level 1 | Equity securities |  |
ASSETS |  |
Nuclear decommissioning trusts: | 19,150 | 11,859
Other special use funds: | 103,354 | 24,962
Level 1 | Equity securities | Pinnacle West Captive Insurance Cell |  |
ASSETS |  |
Other special use funds: |  | 9,200
Level 1 | U.S. commingled equity funds |  |
ASSETS |  |
Nuclear decommissioning trusts: | 0 | 0
Level 1 | U.S. Treasury debt |  |
ASSETS |  |
Nuclear decommissioning trusts: | 352,998 | 367,396
Other special use funds: | 324,411 | 355,544
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 1 | Cash equivalents |  |
ASSETS |  |
Other special use funds: |  | 25,000
Level 1 | Cash equivalents | Pinnacle West Captive Insurance Cell |  |
ASSETS |  |
Other special use funds: |  | 25,000
Level 2 |  |
ASSETS |  |
Cash equivalents | 0 | 0
Nuclear decommissioning trusts: | 531,526 | 477,186
Other special use funds: | 0 | 0
Total assets | 563,969 | 490,338
Level 2 | Commodity contracts |  |
ASSETS |  |
Commodity contracts | 32,443 | 13,152
LIABILITIES |  |
Derivative instruments | (25,218) | (40,388)
Level 2 | Equity securities |  |
ASSETS |  |
Nuclear decommissioning trusts: | 0 | 542
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: | 237,191 | 203,180
Level 2 | Mortgage-backed securities |  |
ASSETS |  |
Nuclear decommissioning trusts: | 232,657 | 208,533
Level 2 | Municipal bonds |  |
ASSETS |  |
Nuclear decommissioning trusts: | 37,785 | 37,429
Level 2 | Other fixed income |  |
ASSETS |  |
Nuclear decommissioning trusts: | 23,893 | 27,502
Level 2 | Cash equivalents |  |
ASSETS |  |
Other special use funds: |  | 0
Level 3 |  |
ASSETS |  |
Cash equivalents | 0 | 0
Nuclear decommissioning trusts: | 0 | 0
Other special use funds: | 0 | 0
Total assets | 1,369 | 7,176
Level 3 | Commodity contracts |  |
ASSETS |  |
Commodity contracts | 1,369 | 7,176
LIABILITIES |  |
Derivative instruments | (19,645) | (22,215)
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
Level 3 | Cash equivalents |  |
ASSETS |  |
Other special use funds: |  | 0
Fair Value Measured at Net Asset Value Per Share | U.S. commingled equity funds |  |
ASSETS |  |
Nuclear decommissioning trusts: |  | $ 423,069
Nuclear decommissioning trust, other | $ 487,681 |

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