Acquisitions and Dispositions (Schedule of Major Classes of Assets and Liabilities Reported As Held for Sale in Discontinued Operations) (Parenthetical) (Detail) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Goodwill	[1]	$ 7,381	$ 7,395	$ 4,859
Dominion Energy Gas Holdings, LLC | GT&S Transaction
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Cash and cash equivalents			20
Goodwill			1,400
Current portions of long-term debt			699
Dominion Energy Gas Holdings, LLC | Q-Pipe Transaction
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Cash and cash equivalents		7	11
Goodwill		$ 191	$ 191

[1] Goodwill amounts do not contain any accumulated impairment losses.