Asset Retirement Obligations - Narrative (Details) - Arizona Public Service Company - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2017
Asset Retirement Obligations
Newly incurred liabilities		$ 22,211
Navajo Generating Station
Asset Retirement Obligations
Newly incurred liabilities	$ 22,000

Amount of asset retirement obligations incurred during the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

Name:	us-gaap_AssetRetirementObligationLiabilitiesIncurred
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration