Long-Term Debt and Liquidity Matters - Estimated Fair Value of Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Estimated fair value of long-term debt, including current maturities
Carrying Amount	$ 4,698,048	$ 4,146,785
Fair Value	5,063,258	4,425,789
Pinnacle West
Estimated fair value of long-term debt, including current maturities
Carrying Amount	125,000	125,000
Fair Value	125,000	125,000
Arizona Public Service Company
Estimated fair value of long-term debt, including current maturities
Carrying Amount	4,573,048	4,021,785
Fair Value	$ 4,938,258	$ 4,300,789