Long-Term Debt and Liquidity Matters - Estimated Fair Value of Long-Term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Estimated fair value of long-term debt, including current maturities
Carrying Amount	$ 5,922,161	$ 5,632,558
Fair Value	6,894,289	6,194,392
Pinnacle West
Estimated fair value of long-term debt, including current maturities
Carrying Amount	496,610	449,425
Fair Value	507,850	450,822
APS
Estimated fair value of long-term debt, including current maturities
Carrying Amount	5,425,551	5,183,133
Fair Value	$ 6,386,439	$ 5,743,570