Regulatory Matters Regulatory Matters - Deferred Fuel and Purchased Power Regulatory Asset (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in regulatory asset
Deferred fuel and purchased power	$ 48,405	$ 60,303	$ (14,997)
Deferred fuel and purchased power amortization	14,767	(38,152)	(1,617)
ARIZONA PUBLIC SERVICE COMPANY
Change in regulatory asset
Deferred fuel and purchased power	48,405	60,303	(14,997)
Deferred fuel and purchased power amortization	14,767	(38,152)	(1,617)
ACC | ARIZONA PUBLIC SERVICE COMPANY | Power Supply Adjustor (PSA)
Change in regulatory asset
Beginning balance	12,465	(9,688)
Deferred fuel and purchased power	48,405	60,303
Deferred fuel and purchased power amortization	14,767	(38,150)
Ending balance	$ 75,637	$ 12,465	$ (9,688)