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Investments in Nuclear Decommissioning Trusts and Other Special Use Funds (Details) - APS - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2022 | Mar. 31, 2021 | Dec. 31, 2021
Nuclear decommissioning trust fund assets |  |  |
Fair Value | $ 1,576,507 |  | $ 1,653,167
Total Unrealized Gains | 431,150 |  | 475,670
Total Unrealized Losses | (36,999) |  | (4,063)
Amortized cost | 991,000 |  | 972,000
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |
Realized gains | 1,023 | $ 2,968 |
Realized losses | (7,235) | (4,148) |
Proceeds from the sale of securities | 361,238 | 379,978 |
Equity securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Equity securities | 611,805 |  | 687,882
Total Unrealized Gains | 422,497 |  | 451,387
Total Unrealized Losses | (37) |  | 0
Available for sale-fixed income securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 963,112 |  | 992,131
Total Unrealized Gains | 8,653 |  | 24,283
Total Unrealized Losses | (36,962) |  | (4,063)
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 100,488 |  |
1 year – 5 years | 385,820 |  |
5 years – 10 years | 185,911 |  |
Greater than 10 years | 290,893 |  |
Total | 963,112 |  |
Other |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 1,590 |  | (26,846)
Total Unrealized Gains | 0 |  | 0
Total Unrealized Losses | 0 |  | 0
Nuclear Decommissioning Trusts |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 1,227,465 |  | 1,294,757
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |
Realized gains | 1,023 | 2,968 |
Realized losses | (7,235) | (4,148) |
Proceeds from the sale of securities | 319,693 | 234,728 |
Nuclear Decommissioning Trusts | Equity securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Equity securities | 584,737 |  | 640,312
Nuclear Decommissioning Trusts | Available for sale-fixed income securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 642,250 |  | 682,227
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 18,119 |  |
1 year – 5 years | 198,233 |  |
5 years – 10 years | 139,957 |  |
Greater than 10 years | 285,941 |  |
Total | 642,250 |  |
Nuclear Decommissioning Trusts | Other |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 478 |  | (27,782)
Other Special Use Funds |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 349,042 |  | 358,410
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |
Realized gains | 0 | 0 |
Realized losses | 0 | 0 |
Proceeds from the sale of securities | 41,545 | $ 145,250 |
Other Special Use Funds | Equity securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Equity securities | 27,068 |  | 47,570
Other Special Use Funds | Available for sale-fixed income securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 320,862 |  | 309,904
Other Special Use Funds | Other |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 1,112 |  | $ 936
Coal Reclamation Escrow Account | Available for sale-fixed income securities |  |  |
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 41,906 |  |
1 year – 5 years | 35,749 |  |
5 years – 10 years | 1,749 |  |
Greater than 10 years | 4,952 |  |
Total | 84,356 |  |
Active Union Employee Medical Account | Available for sale-fixed income securities |  |  |
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 40,463 |  |
1 year – 5 years | 151,838 |  |
5 years – 10 years | 44,205 |  |
Greater than 10 years | 0 |  |
Total | $ 236,506 |  |

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