Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions	9 Months Ended
Sep. 30, 2021 USD ($)
Accounting Policies [Abstract]
Decrease to AROs associated with certain gas distribution pipelines	$ 23
Decrease to utility plant, net	$ 20

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