Acquisitions and Dispositions (Acquisition of Birdseye) (Narrative) (Detail) - USD ($) $ in Millions	1 Months Ended
	May 31, 2021	Sep. 30, 2021	Dec. 31, 2020	[1]
Business Acquisition And Dispositions [Line Items]
Goodwill		$ 7,405	$ 7,381
Birdseye
Business Acquisition And Dispositions [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired	100.00%
Business acquisition, total consideration	$ 46
Business acquisition, cash consideration	28
Business acquisition, fair value of consideration	18
Other deferred charges and other assets	25
Goodwill	$ 24

[1] Dominion Energy’s Consolidated Balance Sheet at December 31, 2020 has been derived from the audited Consolidated Balance Sheet at that date.