Asset Retirement Obligations - Narrative (Details) - APS $ in Millions	3 Months Ended
Jun. 30, 2020 USD ($)
Four Corners
Asset Retirement Obligations
Asset retirement obligation, period increase (decrease)	$ (11)
Navajo Generating Station
Asset Retirement Obligations
Asset retirement obligation, period increase (decrease)	$ 5

Amount of increase (decrease) in asset retirement obligations.

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

Name:	us-gaap_AssetRetirementObligationPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration