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Investments in Nuclear Decommissioning Trusts and Other Special Use Funds (Details) - APS - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019
Nuclear decommissioning trust fund assets |  |  |  |  |
Fair Value | $ 1,338,129 |  | $ 1,338,129 |  | $ 1,255,870
Total Unrealized Gains | 406,270 |  | 406,270 |  | 363,476
Total Unrealized Losses | (710) |  | (710) |  | (669)
Amortized cost | 726,000 |  | 726,000 |  | 691,000
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |  |  |
Realized gains | 2,933 | $ 4,736 | 10,746 | $ 8,482 |
Realized losses | (765) | (2,360) | (4,613) | (5,465) |
Proceeds from the sale of securities | 216,026 | 211,641 | 607,885 | 520,996 |
Equity securities |  |  |  |  |
Nuclear decommissioning trust fund assets |  |  |  |  |
Equity securities | 578,472 |  | 578,472 |  | 536,858
Total Unrealized Gains | 359,112 |  | 359,112 |  | 337,681
Total Unrealized Losses | (36) |  | (36) |  | 0
Available for sale-fixed income securities |  |  |  |  |
Nuclear decommissioning trust fund assets |  |  |  |  |
Fair Value | 772,361 |  | 772,361 |  | 716,137
Total Unrealized Gains | 47,158 |  | 47,158 |  | 25,795
Total Unrealized Losses | (674) |  | (674) |  | (669)
Fair value of fixed income securities, summarized by contractual maturities |  |  |  |  |
Less than one year | 98,163 |  | 98,163 |  |
1 year – 5 years | 318,864 |  | 318,864 |  |
5 years – 10 years | 125,391 |  | 125,391 |  |
Greater than 10 years | 229,943 |  | 229,943 |  |
Total | 772,361 |  | 772,361 |  |
Other |  |  |  |  |
Nuclear decommissioning trust fund assets |  |  |  |  |
Other | (12,704) |  | (12,704) |  | 2,875
Total Unrealized Gains | 0 |  | 0 |  | 0
Total Unrealized Losses | 0 |  | 0 |  | 0
Nuclear Decommissioning Trust |  |  |  |  |
Nuclear decommissioning trust fund assets |  |  |  |  |
Fair Value | 1,069,837 |  | 1,069,837 |  | 1,010,775
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |  |  |
Realized gains | 2,933 | 4,732 | 10,746 | 8,478 |
Realized losses | (750) | (2,360) | (4,598) | (5,465) |
Proceeds from the sale of securities | 178,919 | 155,386 | 534,057 | 371,538 |
Nuclear Decommissioning Trust | Equity securities |  |  |  |  |
Nuclear decommissioning trust fund assets |  |  |  |  |
Equity securities | 570,382 |  | 570,382 |  | 529,716
Nuclear Decommissioning Trust | Available for sale-fixed income securities |  |  |  |  |
Nuclear decommissioning trust fund assets |  |  |  |  |
Fair Value | 513,603 |  | 513,603 |  | 478,658
Fair value of fixed income securities, summarized by contractual maturities |  |  |  |  |
Less than one year | 23,079 |  | 23,079 |  |
1 year – 5 years | 146,885 |  | 146,885 |  |
5 years – 10 years | 122,619 |  | 122,619 |  |
Greater than 10 years | 221,020 |  | 221,020 |  |
Total | 513,603 |  | 513,603 |  |
Nuclear Decommissioning Trust | Other |  |  |  |  |
Nuclear decommissioning trust fund assets |  |  |  |  |
Other | (14,148) |  | (14,148) |  | 2,401
Other Special Use Funds |  |  |  |  |
Nuclear decommissioning trust fund assets |  |  |  |  |
Fair Value | 268,292 |  | 268,292 |  | 245,095
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |  |  |
Realized gains | 0 | 4 | 0 | 4 |
Realized losses | (15) | 0 | (15) | 0 |
Proceeds from the sale of securities | 37,107 | $ 56,255 | 73,828 | $ 149,458 |
Other Special Use Funds | Equity securities |  |  |  |  |
Nuclear decommissioning trust fund assets |  |  |  |  |
Equity securities | 8,090 |  | 8,090 |  | 7,142
Other Special Use Funds | Available for sale-fixed income securities |  |  |  |  |
Nuclear decommissioning trust fund assets |  |  |  |  |
Fair Value | 258,758 |  | 258,758 |  | 237,479
Other Special Use Funds | Other |  |  |  |  |
Nuclear decommissioning trust fund assets |  |  |  |  |
Other | 1,444 |  | 1,444 |  | $ 474
Coal Mine Reclamation Escrow Account | Available for sale-fixed income securities |  |  |  |  |
Fair value of fixed income securities, summarized by contractual maturities |  |  |  |  |
Less than one year | 34,578 |  | 34,578 |  |
1 year – 5 years | 29,041 |  | 29,041 |  |
5 years – 10 years | 2,772 |  | 2,772 |  |
Greater than 10 years | 8,923 |  | 8,923 |  |
Total | 75,314 |  | 75,314 |  |
Active union medical trust | Available for sale-fixed income securities |  |  |  |  |
Fair value of fixed income securities, summarized by contractual maturities |  |  |  |  |
Less than one year | 40,506 |  | 40,506 |  |
1 year – 5 years | 142,938 |  | 142,938 |  |
5 years – 10 years | 0 |  | 0 |  |
Greater than 10 years | 0 |  | 0 |  |
Total | $ 183,444 |  | $ 183,444 |  |

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