Long-Term Debt and Liquidity Matters - Estimated Fair Value of Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Estimated fair value of long-term debt, including current maturities
Carrying Amount	$ 5,136,108	$ 5,138,232
Fair Value	5,388,892	5,233,563
Pinnacle West
Estimated fair value of long-term debt, including current maturities
Carrying Amount	448,953	448,796
Fair Value	446,835	443,955
APS
Estimated fair value of long-term debt, including current maturities
Carrying Amount	4,687,155	4,689,436
Fair Value	$ 4,942,057	$ 4,789,608