Investments (Narrative) (Detail) - USD ($)		1 Months Ended		3 Months Ended		9 Months Ended
		Nov. 30, 2020	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Schedule Of Debt And Equity Securities [Line Items]
Earnings (loss) from equity method investees				$ 69,000,000	$ (5,000,000)	$ 214,000,000	$ 0
Net losses from discontinued operations including noncontrolling interest	[1],[2]			65,000,000	19,000,000	119,000,000	(1,753,000,000)
Distributions received from investment						263,000,000	25,000,000
Equity method affiliates includes cash and accrued amounts of contributions						1,000,000,000.0	93,000,000
Acquisition of equity method affiliates							178,000,000
Equity method investment goodwill				27,000,000		27,000,000		$ 27,000,000
Income loss from continuing operations before income taxes extraordinary items noncontrolling interest				636,000,000	2,000,000	2,050,000,000	390,000,000
Contributions to equity method affiliates						1,006,000,000	92,000,000
Current liabilities				1,050,000,000		1,050,000,000		625,000,000	[3]
Credit facility, amount borrowed				900,000,000		900,000,000
Guarantee liability	[4]			3,851,000,000		3,851,000,000
Revenue				3,434,000,000	$ 3,536,000,000	10,358,000,000	$ 10,350,000,000
Assets				9,298,000,000		9,298,000,000		6,886,000,000	[3]
Liabilities				13,223,000,000		13,223,000,000		10,843,000,000	[3]
Retail Energy Marketing Operations
Schedule Of Debt And Equity Securities [Line Items]
Assets				81,000,000		81,000,000		63,000,000
Liabilities				21,000,000		21,000,000		15,000,000
Cove Point
Schedule Of Debt And Equity Securities [Line Items]
Ownership interest percentage of general partners		100.00%
Fowler Ridge
Schedule Of Debt And Equity Securities [Line Items]
Percentage of equity interest sold to noncontrolling interest owners			50.00%		50.00%		50.00%
Net payment of long-term power and capacity contract			$ 150,000,000
Contract termination loss					$ 221,000,000		$ 221,000,000
Contract termination loss net of tax					165,000,000		165,000,000
Maximum
Schedule Of Debt And Equity Securities [Line Items]
Earnings (loss) from equity method investees							1,000,000
Atlantic Coast Pipeline
Schedule Of Debt And Equity Securities [Line Items]
Net losses from discontinued operations including noncontrolling interest						(19,000,000)	(2,300,000,000)
Contributions to equity method affiliates				0	45,000,000	965,000,000	74,000,000
Atlantic Coast Pipeline | Dominion Energy Transmission Inc
Schedule Of Debt And Equity Securities [Line Items]
Revenue					7,000,000		44,000,000
Atlantic Coast Pipeline | Financial Guarantee
Schedule Of Debt And Equity Securities [Line Items]
Guarantee liability								6,000,000
Atlantic Coast Pipeline | Revolving Credit Facility
Schedule Of Debt And Equity Securities [Line Items]
Credit facility, amount borrowed								1,800,000,000
Atlantic Coast Pipeline | Other Current Liabilities
Schedule Of Debt And Equity Securities [Line Items]
Current liabilities				112,000,000		112,000,000		1,100,000,000
Cove Point
Schedule Of Debt And Equity Securities [Line Items]
Distributions received from investment				85,000,000		235,000,000
Income loss from continuing operations before income taxes extraordinary items noncontrolling interest				136,000,000	$ 132,000,000	410,000,000	$ 396,000,000
Contributions to equity method affiliates				0		0
Cove Point | Cove Point | GT&S Transaction
Schedule Of Debt And Equity Securities [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 Debt And Equity Securities [Line Items]
Carrying amount of investment that exceeded share of underlying equity				231,000,000		231,000,000		213,000,000
Equity method investment goodwill				(18,000,000)		(18,000,000)		(41,000,000)
Finite Lived Equity Method Investment Basis Difference | Cove Point
Schedule Of Debt And Equity Securities [Line Items]
Equity method investment goodwill				222,000,000		222,000,000		227,000,000
Trading Securities
Schedule Of Debt And Equity Securities [Line Items]
Rabbi trust securities				$ 122,000,000		$ 122,000,000		$ 134,000,000

[1] Includes income tax expense (benefit) of $(6) million and $(10) million for the three months ended September 30, 2021 and 2020, respectively, and $5 million and $(572) million for the nine months ended September 30, 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 property 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.