Acquisitions and Dispositions (Schedule of Major Classes of Assets and Liabilities Reported As Held for Sale in Discontinued Operations) (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Goodwill	$ 7,395	$ 7,395	[1]
Dominion Energy Gas Holdings, LLC | Gas, Transmission & Storage
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Cash, restricted cash and equivalents of discontinued operations	24	20
Goodwill	1,400	1,400
Current portions of long-term debt	1,200	699
Dominion Energy Gas Holdings, LLC | Gas, Transmission & Storage | Supply Header Project
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Property, plant and equipment	40
Asset retirement obligation, Current	47
Dominion Energy Gas Holdings, LLC | Q-Pipe Transaction
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Cash, restricted cash and equivalents of discontinued operations	25	11
Goodwill	$ 191	$ 191

[1] Dominion Energy’s Consolidated Balance Sheet at December 31, 2019 has been derived from the audited Consolidated Balance Sheet at that date.