Long-Term Debt and Liquidity Matters - Estimated Fair Value of Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Estimated fair value of long-term debt, including current maturities
Carrying Amount	$ 6,316,420	$ 5,632,558
Fair Value	7,393,608	6,194,392
Pinnacle West
Estimated fair value of long-term debt, including current maturities
Carrying Amount	496,117	449,425
Fair Value	507,500	450,822
APS
Estimated fair value of long-term debt, including current maturities
Carrying Amount	5,820,303	5,183,133
Fair Value	$ 6,886,108	$ 5,743,570