Investments (Narrative) (Detail) - USD ($)		1 Months Ended	3 Months Ended
		Sep. 30, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Equity in earnings(losses) on investments			$ 80,000,000	$ 4,000,000
Net income (loss) from discontinued operations including noncontrolling interest	[1],[2]		28,000,000	229,000,000
Distributions received from investment			73,000,000	5,000,000
Carrying amount of investment that exceeded share of underlying equity			224,000,000		$ 213,000,000
Equity method investment goodwill			27,000,000		27,000,000
Income loss from continuing operations before income taxes extraordinary items noncontrolling interest			1,192,000,000	(518,000,000)
Contributions to equity method affiliates			977,000,000	11,000,000
Current liabilities			625,000,000		625,000,000	[3]
Guarantee liability	[4]		3,498,000,000
Revenue			3,840,000,000	3,827,000,000
Assets			6,662,000,000		6,886,000,000	[3]
Liabilities			11,836,000,000		10,843,000,000	[3]
Retail Energy Marketing Operations
Schedule of Equity Method Investments [Line Items]
Assets			72,000,000		63,000,000
Liabilities			15,000,000		15,000,000
Cove Point
Schedule of Equity Method Investments [Line Items]
Ownership interest percentage of limited partner interests		100.00%
Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Net income (loss) from discontinued operations including noncontrolling interest			(8,000,000)	35,000,000
Contributions to equity method affiliates			965,000,000	16,000,000
Atlantic Coast Pipeline | DETI
Schedule of Equity Method Investments [Line Items]
Revenue				20,000,000
Atlantic Coast Pipeline | Financial Guarantee
Schedule of Equity Method Investments [Line Items]
Guarantee liability					6,000,000
Atlantic Coast Pipeline | Revolving Credit Facility
Schedule of Equity Method Investments [Line Items]
Credit facility, amount borrowed					1,800,000,000
Atlantic Coast Pipeline | Other Current Liabilities
Schedule of Equity Method Investments [Line Items]
Current liabilities			97,000,000		1,100,000,000
Cove Point
Schedule of Equity Method Investments [Line Items]
Distributions received from investment			73,000,000
Income loss from continuing operations before income taxes extraordinary items noncontrolling interest			138,000,000	$ 133,000,000
Contributions to equity method affiliates			0
Cove Point | Cove Point | GT&S Transaction
Schedule of Equity Method Investments [Line Items]
Percentage of limited partner interest sold		25.00%
Percentage of noncontrolling limited partnership interest retained		50.00%
Finite Lived Equity Method Investment Basis Difference
Schedule of Equity Method Investments [Line Items]
Equity method investment goodwill			(29,000,000)		(41,000,000)
Finite Lived Equity Method Investment Basis Difference | Cove Point
Schedule of Equity Method Investments [Line Items]
Equity method investment goodwill			226,000,000		227,000,000
Trading Securities
Schedule of Equity Method Investments [Line Items]
Rabbi trust securities			$ 139,000,000		$ 134,000,000

[1] Includes income tax expense of $7 million and $31 million for the three months ended March 31, 2021 and 2020, respectively.

[2] See Note 10 for amounts attributable to related parties.

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

[4] Excludes Dominion Energy's guarantees for the new corporate office properties and an offshore wind installation vessel discussed in Note 15 to the Consolidated Financial Statements in the Companies’ Annual Report on Form 10-K for the year ended December 31, 2020 and in Note 14 in this report.