Long-Term Debt and Liquidity Matters - Estimated Fair Value of Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Estimated fair value of long-term debt, including current maturities
Carrying Amount	$ 5,434,996	$ 5,138,232
Fair Value	6,067,397	5,233,563
Pinnacle West
Estimated fair value of long-term debt, including current maturities
Carrying Amount	449,268	448,796
Fair Value	449,670	443,955
APS
Estimated fair value of long-term debt, including current maturities
Carrying Amount	4,985,728	4,689,436
Fair Value	$ 5,617,727	$ 4,789,608