Long-Term Debt and Liquidity Matters - Estimated Fair Value of Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Estimated fair value of long-term debt, including current maturities
Carrying Amount	$ 5,483,324	$ 5,632,558
Fair Value	6,082,714	6,194,392
Pinnacle West
Estimated fair value of long-term debt, including current maturities
Carrying Amount	449,581	449,425
Fair Value	448,449	450,822
APS
Estimated fair value of long-term debt, including current maturities
Carrying Amount	5,033,743	5,183,133
Fair Value	$ 5,634,265	$ 5,743,570