Long-Term Debt and Liquidity Matters - Estimated Fair Value of Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Estimated fair value of long-term debt, including current maturities
Carrying Amount	$ 4,872,533	$ 4,871,713
Fair Value	5,138,726	5,304,956
Pinnacle West
Estimated fair value of long-term debt, including current maturities
Carrying Amount	298,326	298,421
Fair Value	293,061	298,608
Arizona Public Service Company
Estimated fair value of long-term debt, including current maturities
Carrying Amount	4,574,207	4,573,292
Fair Value	$ 4,845,665	$ 5,006,348