Long-Term Debt and Liquidity Matters - Estimated Fair Value of Long-Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Estimated fair value of long-term debt, including current maturities
Carrying Amount	$ 3,669	$ 3,415
Fair Value	3,994	3,839
Pinnacle West
Estimated fair value of long-term debt, including current maturities
Carrying Amount	125	125
Fair Value	125	125
Arizona Public Service Company
Estimated fair value of long-term debt, including current maturities
Carrying Amount	3,544	3,290
Fair Value	$ 3,869	$ 3,714