Asset Retirement Obligations (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) turbine_unit
ARIZONA PUBLIC SERVICE COMPANY
Change in asset retirement obligations
Asset retirement obligations at the beginning of year	$ 624,475	$ 443,576
Changes attributable to:
Accretion expense	33,104	26,656
Settlements	0	(15,732)
Estimated cash flow revisions	21,950	151,046
Newly incurred or acquired obligations	0	18,929
Asset retirement obligations at the end of year	679,529	$ 624,475
Navajo Generating Station | ARIZONA PUBLIC SERVICE COMPANY
Asset Retirement Obligations
Increase in regulatory asset	2,000
Decrease in regulatory liability	20,000
Changes attributable to:
Newly incurred or acquired obligations	$ 22,000
Ocotillo Steam Units | ARIZONA PUBLIC SERVICE COMPANY
Asset Retirement Obligations
Number of constructed turbine units | turbine_unit		5
Changes attributable to:
Newly incurred or acquired obligations		$ 10,000
El Paso's Share of Four Corners Units 4 & 5 | 4CA
Changes attributable to:
Newly incurred or acquired obligations		9,000
Four Corners | ARIZONA PUBLIC SERVICE COMPANY
Changes attributable to:
Settlements		(16,000)
Palo Verde Nuclear Generating Station | ARIZONA PUBLIC SERVICE COMPANY
Asset Retirement Obligations
Decrease in regulatory liability		20,000
Increase in plant services		131,000
Changes attributable to:
Estimated cash flow revisions		$ 151,000