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Investments in Nuclear Decommissioning Trusts and Other Special Use Funds (Details) - ARIZONA PUBLIC SERVICE COMPANY - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Nuclear decommissioning trust fund assets |  |  |
Fair Value | $ 1,087,235 | $ 901,358 |
Total Unrealized Gains | 230,781 | 260,160 |
Total Unrealized Losses | (7,237) | (2,996) |
Amortized cost | 635,000 | 467,000 |
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |
Realized gains | 6,680 | 21,830 | $ 11,213
Realized losses | (13,552) | (13,155) | (10,106)
Proceeds from the sale of securities | 653,033 | 546,339 | 633,410
Equity securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 447,138 | 425,044 |
Total Unrealized Gains | 222,147 | 248,623 |
Total Unrealized Losses | (459) | 0 |
Fixed income securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 637,356 | 475,716 |
Total Unrealized Gains | 8,634 | 11,537 |
Total Unrealized Losses | (6,778) | (2,996) |
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 88,022 |  |
1 year - 5 years | 217,352 |  |
5 years - 10 years | 130,890 |  |
Greater than 10 years | 201,092 |  |
Total | 637,356 |  |
Other Receivables from Broker-Dealers and Clearing |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 2,741 | 598 |
Total Unrealized Gains | 0 | 0 |
Total Unrealized Losses | 0 | 0 |
Nuclear Decommissioning Trusts |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 851,134 | 871,000 |
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |
Realized gains | 6,679 | 21,813 | 11,213
Realized losses | (13,552) | (13,146) | (10,106)
Proceeds from the sale of securities | 554,385 | 542,246 | 633,410
Nuclear Decommissioning Trusts | Equity securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 402,008 | 424,614 |
Nuclear Decommissioning Trusts | Fixed income securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 446,978 | 446,277 |
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 26,819 |  |
1 year - 5 years | 97,566 |  |
5 years - 10 years | 128,379 |  |
Greater than 10 years | 194,214 |  |
Total | 446,978 |  |
Nuclear Decommissioning Trusts | Other Receivables from Broker-Dealers and Clearing |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 2,148 | 109 |
Coal Reclamation Escrow Accounts | Fixed income securities |  |  |
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 21,237 |  |
1 year - 5 years | 15,658 |  |
5 years - 10 years | 2,511 |  |
Greater than 10 years | 6,878 |  |
Total | 46,284 |  |
Active Union Medical Trust | Fixed income securities |  |  |
Fair value of fixed income securities, summarized by contractual maturities |  |  |
Less than one year | 39,966 |  |
1 year - 5 years | 104,128 |  |
5 years - 10 years | 0 |  |
Greater than 10 years | 0 |  |
Total | 144,094 |  |
Other Special Use Funds |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 236,101 | 30,358 |
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds |  |  |
Realized gains | 1 | 17 | 0
Realized losses | 0 | (9) | 0
Proceeds from the sale of securities | 98,648 | 4,093 | $ 0
Other Special Use Funds | Equity securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 45,130 | 430 |
Other Special Use Funds | Fixed income securities |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | 190,378 | 29,439 |
Other Special Use Funds | Other Receivables from Broker-Dealers and Clearing |  |  |
Nuclear decommissioning trust fund assets |  |  |
Fair Value | $ 593 | $ 489 |

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