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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, 2023 | Mar. 31, 2022 | Dec. 31, 2022
Nuclear decommissioning trust fund assets |  |  |
Fair Value | $ 1,478,494 |  | $ 1,420,641
Total Unrealized Gains | 374,520 |  | 337,994
Total Unrealized Losses | (54,228) |  | (69,091)
Amortized cost | 981,000 |  | 927,000
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |
Realized gains | 1,210 | $ 1,023 |
Realized losses | (5,694) | (7,235) |
Proceeds from the sale of securities | 226,626 | 361,238 |
Nuclear Decommissioning Trusts |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 1,125,617 |  | 1,073,410
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |
Realized gains | 1,210 | 1,023 |
Realized losses | (5,694) | (7,235) |
Proceeds from the sale of securities | 136,185 | 319,693 |
Other Special Use Funds |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 352,877 |  | 347,231
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 | 90,441 | $ 41,545 |
Equity securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Equity securities | 545,013 |  | 554,214
Total Unrealized Gains | 367,791 |  | 334,817
Total Unrealized Losses | (39) |  | (267)
Equity securities | Nuclear Decommissioning Trusts |  |  |
Nuclear decommissioning trust fund assets |  |  |
Equity securities | 517,371 |  | 487,240
Equity securities | Other Special Use Funds |  |  |
Nuclear decommissioning trust fund assets |  |  |
Equity securities | 27,642 |  | 66,974
Available for sale-fixed income securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 933,575 |  | 861,637
Total Unrealized Gains | 6,728 |  | 3,177
Total Unrealized Losses | (54,178) |  | (68,795)
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 143,097 |  |
1 year – 5 years | 321,766 |  |
5 years – 10 years | 182,543 |  |
Greater than 10 years | 286,169 |  |
Total | 933,575 |  |
Available for sale-fixed income securities | Nuclear Decommissioning Trusts |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 609,381 |  | 582,343
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 14,591 |  |
1 year – 5 years | 174,911 |  |
5 years – 10 years | 137,708 |  |
Greater than 10 years | 282,171 |  |
Total | 609,381 |  |
Available for sale-fixed income securities | Other Special Use Funds |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 324,194 |  | 279,294
Available for sale-fixed income securities | Coal Reclamation Escrow Account |  |  |
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 53,718 |  |
1 year – 5 years | 36,821 |  |
5 years – 10 years | 0 |  |
Greater than 10 years | 3,998 |  |
Total | 94,537 |  |
Available for sale-fixed income securities | Active Union Employee Medical Account |  |  |
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 74,788 |  |
1 year – 5 years | 110,034 |  |
5 years – 10 years | 44,835 |  |
Greater than 10 years | 0 |  |
Total | 229,657 |  |
Other |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | (94) |  | 4,790
Total Unrealized Gains | 1 |  | 0
Total Unrealized Losses | (11) |  | (29)
Other | Nuclear Decommissioning Trusts |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | (1,135) |  | 3,827
Other | Other Special Use Funds |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | $ 1,041 |  | $ 963

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