Investments (Narrative) (Detail) - USD ($)		1 Months Ended	3 Months Ended		6 Months Ended
		Nov. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investees			$ 65,000,000	$ 2,000,000	$ 145,000,000	$ 5,000,000
Net losses from discontinued operations including noncontrolling interest	[1],[2]		26,000,000	(2,001,000,000)	54,000,000	(1,772,000,000)
Distributions received from investment					166,000,000	46,000,000
Equity method affiliates includes cash and accrued amounts of contributions					1,000,000,000.0	37,000,000
Other liabilities current	[2]		2,114,000,000		2,114,000,000		$ 1,933,000,000	[3]
Contributions to equity method affiliates					0	178,000,000
Carrying amount of investment that exceeded share of underlying equity			234,000,000		234,000,000		213,000,000
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			222,000,000	906,000,000	1,414,000,000	388,000,000
Contributions to equity method affiliates					983,000,000	39,000,000
Current liabilities			631,000,000		631,000,000		625,000,000	[3]
Credit facility, amount borrowed			250,000,000		250,000,000
Guarantee liability	[4]		3,781,000,000		3,781,000,000
Revenue			3,084,000,000	3,002,000,000	6,924,000,000	6,792,000,000
Assets			6,923,000,000		6,923,000,000		6,886,000,000	[3]
Liabilities			11,676,000,000		11,676,000,000		10,843,000,000	[3]
Retail Energy Marketing Operations
Schedule of Equity Method Investments [Line Items]
Assets			60,000,000		60,000,000		63,000,000
Liabilities			17,000,000		17,000,000		15,000,000
Cove Point
Schedule of Equity Method Investments [Line Items]
Ownership interest percentage of general partners		100.00%
Dominion Energy Transmission Inc
Schedule of Equity Method Investments [Line Items]
Other liabilities current				20,000,000		20,000,000
Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Net losses from discontinued operations including noncontrolling interest					(22,000,000)	(2,300,000,000)
Contributions to equity method affiliates			0	13,000,000	965,000,000	29,000,000
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			115,000,000		115,000,000		1,100,000,000
Atlantic Coast Pipeline | Dominion Energy Transmission Inc
Schedule of Equity Method Investments [Line Items]
Revenue				17,000,000		37,000,000
Cove Point
Schedule of Equity Method Investments [Line Items]
Distributions received from investment			77,000,000		150,000,000
Income loss from continuing operations before income taxes extraordinary items noncontrolling interest			136,000,000	$ 131,000,000	274,000,000	$ 264,000,000
Contributions to equity method affiliates			0		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			(17,000,000)		(17,000,000)		(41,000,000)
Finite Lived Equity Method Investment Basis Difference | Cove Point
Schedule of Equity Method Investments [Line Items]
Equity method investment goodwill			224,000,000		224,000,000		227,000,000
Trading Securities
Schedule of Equity Method Investments [Line Items]
Rabbi trust securities			$ 117,000,000		$ 117,000,000		$ 134,000,000

[1] Includes income tax expense (benefit) of $4 million and $(593) million for the three months ended June 30, 2021 and 2020, respectively, and $11 million and $(562) million for the six months ended June 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.