Long-Term Debt and Liquidity Matters - Fair Value of Long-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Estimated fair value of long-term debt, including current maturities
Carrying Amount	$ 4,871,713	$ 4,146,785
Fair Value	5,304,956	4,425,789
Pinnacle West
Estimated fair value of long-term debt, including current maturities
Carrying Amount	298,421	125,000
Fair Value	298,608	125,000
ARIZONA PUBLIC SERVICE COMPANY
Estimated fair value of long-term debt, including current maturities
Carrying Amount	4,573,292	4,021,785
Fair Value	$ 5,006,348	$ 4,300,789