Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 5,135,730	$ 4,935,912
Reclassification of income tax effect related to tax reform	0
Balance at end of period	5,153,671	4,965,940
Pension and Other Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(42,440)	(39,070)
OCI (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	900	522
Reclassification of income tax effect related to tax reform	(7,954)
Balance at end of period	(49,494)	(38,548)
Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(2,562)	(4,752)
OCI (loss) before reclassifications	(96)	(770)
Amounts reclassified from accumulated other comprehensive loss	409	1,207
Reclassification of income tax effect related to tax reform	(598)
Balance at end of period	(2,847)	(4,315)
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(45,002)	(43,822)
OCI (loss) before reclassifications	(96)	(770)
Amounts reclassified from accumulated other comprehensive loss	1,309	1,729
Reclassification of income tax effect related to tax reform	(8,552)
Balance at end of period	(52,341)	(42,863)
Arizona Public Service Company
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	5,385,869	5,037,970
Balance at end of period	5,401,512	5,067,052
Arizona Public Service Company | Pension and Other Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(24,421)	(20,671)
OCI (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	857	611
Reclassification of income tax effect related to tax reform	(4,440)
Balance at end of period	(28,004)	(20,060)
Arizona Public Service Company | Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(2,562)	(4,752)
OCI (loss) before reclassifications	(96)	(770)
Amounts reclassified from accumulated other comprehensive loss	409	1,207
Reclassification of income tax effect related to tax reform	(598)
Balance at end of period	(2,847)	(4,315)
Arizona Public Service Company | Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(26,983)	(25,423)
OCI (loss) before reclassifications	(96)	(770)
Amounts reclassified from accumulated other comprehensive loss	1,266	1,818
Reclassification of income tax effect related to tax reform	(5,038)
Balance at end of period	$ (30,851)	$ (24,375)