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Investments in Nuclear Decommissioning Trusts and Other Special Use Funds (Tables) | 12 Months Ended
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Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract] |
Schedule of Fair Value of APS's Nuclear Decommissioning Trust Fund Assets | The following tables present the unrealized gains and losses based on the original cost of the investment and summarizes the fair value of APS’s nuclear decommissioning trusts and other special use fund assets (dollars in thousands):
| December 31, 2023
| Fair Value |  | Total Unrealized Gains |  | Total Unrealized Losses
Investment Type: | Nuclear Decommissioning Trusts |  | Other Special Use Funds |  | Total |  |
Equity securities | $ | 420,680 |  |  | $ | 40,991 |  |  | $ | 461,671 |  |  | $ | 336,555 |  |  | $ | — |
Available for sale-fixed income securities | 781,333 |  |  | 319,594 |  |  | 1,100,927 |  | (a) | 21,518 |  |  | (40,868) |
Other | (767) |  |  | 2,196 |  |  | 1,429 |  | (b) | 39 |  |  | — |
Total | $ | 1,201,246 |  |  | $ | 362,781 |  |  | $ | 1,564,027 |  |  | $ | 358,112 |  |  | $ | (40,868) |
(a)As of December 31, 2023, the amortized cost basis of these available-for-sale investments is $1,120 million. (b)Represents net pending securities sales and purchases.
| December 31, 2022
| Fair Value |  | Total Unrealized Gains |  | Total Unrealized Losses
Investment Type: | Nuclear Decommissioning Trusts |  | Other Special Use Funds |  | Total |  |
Equity securities | $ | 487,240 |  |  | $ | 66,974 |  |  | $ | 554,214 |  |  | $ | 334,817 |  |  | $ | (267) |
Available for sale-fixed income securities | 582,343 |  |  | 279,294 |  |  | 861,637 |  | (a) | 3,177 |  |  | (68,795) |
Other | 3,827 |  |  | 963 |  |  | 4,790 |  | (b) | — |  |  | (29) |
Total | $ | 1,073,410 |  |  | $ | 347,231 |  |  | $ | 1,420,641 |  |  | $ | 337,994 |  |  | $ | (69,091) |
(a)As of December 31, 2022, the amortized cost basis of these available-for-sale investments is $927 million. (b)Represents net pending securities sales and purchases.
Schedule of Realized Gains and Losses and Proceeds from the Sale of Securities by the Nuclear Decommissioning Trust Funds | The following table sets forth APS’s realized gains and losses relating to the sale and maturity of available-for-sale debt securities and equity securities, and the proceeds from the sale and maturity of these investment securities (dollars in thousands):
| Year Ended December 31,
| Nuclear Decommissioning Trusts |  | Other Special Use Funds |  | Total
2023 |  |  |  |  |
Realized gains | $ | 111,922 |  |  | $ | 172 |  |  | $ | 112,094 |
Realized losses | $ | (41,212) |  |  | $ | (568) |  |  | $ | (41,780) |
Proceeds from the sale of securities (a) | $ | 1,324,978 |  |  | $ | 354,744 |  |  | $ | 1,679,722 |
2022 |  |  |  |  |
Realized gains | $ | 9,017 |  |  | $ | 420 |  |  | $ | 9,437 |
Realized losses | $ | (40,239) |  |  | $ | — |  |  | $ | (40,239) |
Proceeds from the sale of securities (a) | $ | 979,639 |  |  | $ | 227,558 |  |  | $ | 1,207,197 |
2021 |  |  |  |  |
Realized gains | $ | 134,610 |  |  | $ | 49 |  |  | $ | 134,659 |
Realized losses | $ | (8,431) |  |  | $ | (7) |  |  | $ | (8,438) |
Proceeds from the sale of securities (a) | $ | 1,457,305 |  |  | $ | 263,661 |  |  | $ | 1,720,966 |
(a)Proceeds are reinvested in the nuclear decommissioning trusts and other special use funds, excluding amounts reimbursed to the Company for active union employee medical claims from the active union employee medical account.
Schedule of Fair Value of Fixed Income Securities, Summarized by Contractual Maturities | The fair value of APS’s fixed income securities, summarized by contractual maturities, at December 31, 2023, is as follows (dollars in thousands):
| Nuclear Decommissioning Trusts |  | Coal Reclamation Escrow Account |  | Active Union Employee Medical Account |  | Total
Less than one year | $ | 26,057 |  |  | $ | 58,692 |  |  | $ | 36,857 |  |  | $ | 121,606 |
1 year – 5 years | 225,891 |  |  | 46,120 |  |  | 152,761 |  |  | 424,772 |
5 years – 10 years | 176,288 |  |  | — |  |  | 25,164 |  |  | 201,452 |
Greater than 10 years | 353,097 |  |  | — |  |  | — |  |  | 353,097 |
Total | $ | 781,333 |  |  | $ | 104,812 |  |  | $ | 214,782 |  |  | $ | 1,100,927 |

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