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Investments in Nuclear Decommissioning Trusts and Other Special Use Funds (Details) - USD ($) $ in Thousands | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017
Arizona Public Service Company |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | $ 1,077,239 |  | $ 901,358
Unrealized Gains | 250,485 |  | 260,160
Unrealized Losses | (8,606) |  | (2,996)
Available-for-sale securities, amortized cost basis | 642,000 |  | 467,000
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |
Realized gains | 815 | $ 2,367 |
Realized losses | (2,047) | (2,454) |
Proceeds from the sale of securities | 133,011 | 153,647 |
Arizona Public Service Company | Equity Securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 434,906 |  | 425,044
Unrealized Gains | 242,784 |  | 248,623
Unrealized Losses | (61) |  | 0
Arizona Public Service Company | Fixed income securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 640,942 |  | 475,716
Unrealized Gains | 7,701 |  | 11,537
Unrealized Losses | (8,545) |  | (2,996)
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 46,468 |  |
1 year – 5 years | 260,798 |  |
5 years – 10 years | 127,942 |  |
Greater than 10 years | 205,734 |  |
Total | 640,942 |  |
Arizona Public Service Company | Other |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 1,391 |  | 598
Unrealized Gains | 0 |  | 0
Unrealized Losses | 0 |  | 0
Nuclear Decommissioning Trusts | Arizona Public Service Company |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 861,439 |  | 871,000
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |
Realized gains | 814 | 2,367 |
Realized losses | (2,047) | (2,453) |
Proceeds from the sale of securities | 130,456 |  |
Nuclear Decommissioning Trusts | Arizona Public Service Company | Equity Securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 420,265 |  | 424,614
Nuclear Decommissioning Trusts | Arizona Public Service Company | Fixed income securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 441,241 |  | 446,277
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |
Proceeds from the sale of securities |  | 151,126 |
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 16,148 |  |
1 year – 5 years | 109,466 |  |
5 years – 10 years | 125,206 |  |
Greater than 10 years | 190,421 |  |
Total | 441,241 |  |
Nuclear Decommissioning Trusts | Arizona Public Service Company | Other |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | (67) |  | 109
Other Special Use Funds | Arizona Public Service Company |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 215,800 |  | 30,358
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |
Realized gains | 1 | 0 |
Realized losses | 0 | (1) |
Proceeds from the sale of securities | 2,555 |  |
Other Special Use Funds | Arizona Public Service Company | Equity Securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 14,641 |  | 430
Other Special Use Funds | Arizona Public Service Company | Fixed income securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 199,701 |  | 29,439
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |
Proceeds from the sale of securities |  | $ 2,521 |
Other Special Use Funds | Arizona Public Service Company | Other |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 1,458 |  | 489
Coal Reclamation Escrow Accounts | Arizona Public Service Company | Fixed income securities |  |  |
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 0 |  |
1 year – 5 years | 7,541 |  |
5 years – 10 years | 2,736 |  |
Greater than 10 years | 15,313 |  |
Total | 25,590 |  |
Coal Reclamation Escrow Accounts | 4CA |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 2,000 |  | $ 2,000
Active Union Medical Trust | Arizona Public Service Company | Fixed income securities |  |  |
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 30,320 |  |
1 year – 5 years | 143,791 |  |
5 years – 10 years | 0 |  |
Greater than 10 years | 0 |  |
Total | $ 174,111 |  |

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