Long-Term Debt and Liquidity Matters - Estimated Fair Value of Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Estimated fair value of long-term debt, including current maturities
Carrying Amount	$ 6,913,146	$ 6,314,266
Fair Value	7,732,053	7,612,841
APS
Estimated fair value of long-term debt, including current maturities
Carrying Amount	6,266,212	5,817,945
Fair Value	7,080,893	7,103,791
Pinnacle West
Estimated fair value of long-term debt, including current maturities
Carrying Amount	646,934	496,321
Fair Value	$ 651,160	$ 509,050