Investments (Narrative) (Detail)		1 Months Ended			3 Months Ended			9 Months Ended		12 Months Ended
		Sep. 30, 2020 USD ($)	Oct. 31, 2017 USD ($)	Sep. 30, 2014 mi	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2018	Jul. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Schedule of Equity Method Investments [Line Items]
Equity in earnings(losses) on investments									$ 5,000,000
Net income (loss) from discontinued operations including noncontrolling interest	[1],[2]				$ 19,000,000	$ 38,000,000		$ (1,753,000,000)	526,000,000
Distributions received from investment								25,000,000	28,000,000
Carrying amount of investment that exceeded share of underlying equity		$ (19,000,000)			(19,000,000)			(19,000,000)					$ (35,000,000)
Equity method investment goodwill		27,000,000			27,000,000			27,000,000					11,000,000
Current liabilities		6,880,000,000			6,880,000,000			6,880,000,000					1,039,000,000	[3]
Maximum obligation amount under credit facility	[4],[5]	6,000,000,000			6,000,000,000			6,000,000,000
Guarantee liability	[6]	5,717,000,000			5,717,000,000			5,717,000,000
Cumulative-effect of changes in accounting principles		4,035,000,000			4,035,000,000			4,035,000,000					7,576,000,000	[3]
Contributions to equity method affiliates								92,000,000	187,000,000
Other payables	[2]	2,376,000,000			2,376,000,000			2,376,000,000					1,738,000,000	[3]
Revenue					3,536,000,000	3,623,000,000		10,350,000,000	9,993,000,000
Other receivables		174,000,000			174,000,000			174,000,000					340,000,000	[3]
Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Equity in earnings(losses) on investments					(61,000,000)	31,000,000		(2,300,000,000)	84,000,000
Cost to acquire equity method investments												$ 184,000,000
Equity in earnings(losses) on investments after tax					(45,000,000)	31,000,000		(1,800,000,000)	85,000,000
Contributions to equity method affiliates					45,000,000	47,000,000		74,000,000	175,000,000
Atlantic Coast Pipeline | Financial Guarantee
Schedule of Equity Method Investments [Line Items]
Guarantee liability													14,000,000
Atlantic Coast Pipeline | Revolving Credit Facility
Schedule of Equity Method Investments [Line Items]
Maximum obligation amount under credit facility			$ 3,400,000,000								$ 1,900,000,000
Credit facility, maturity date			Oct. 31, 2021
Credit facility, amount borrowed		1,800,000,000			1,800,000,000			1,800,000,000
Atlantic Coast Pipeline | Revolving Credit Facility | Financial Guarantee | Cumulative Effect Period Of Adoption Adjustment
Schedule of Equity Method Investments [Line Items]
Cumulative-effect of changes in accounting principles		(48,000,000)			(48,000,000)			(48,000,000)
Atlantic Coast Pipeline | Other Current Liabilities
Schedule of Equity Method Investments [Line Items]
Current liabilities		1,100,000,000			1,100,000,000			1,100,000,000
Atlantic Coast Pipeline | Dominion Energy Gas Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage acquired												5.00%
Percentage ownership in total units												53.00%
Atlantic Coast Pipeline | DETI
Schedule of Equity Method Investments [Line Items]
Other payables		$ 15,000,000			15,000,000			15,000,000					7,000,000
Revenue					$ 7,000,000	$ 24,000,000		$ 44,000,000	81,000,000
Atlantic Coast Pipeline | Pipelines | Jointly Owned Natural Gas Pipeline | Distribution
Schedule of Equity Method Investments [Line Items]
Length of natural gas pipeline (in miles) | mi				600
Duration of contract				20 years
Blue Racer
Schedule of Equity Method Investments [Line Items]
Additional consideration including interest received in connection with sale							$ 151,000,000
Ownership interest percentage of limited partner interests										50.00%
Fowler Ridge
Schedule of Equity Method Investments [Line Items]
Percentage of interest held		50.00%			50.00%			50.00%
Net payment of long-term power and capacity contract		$ 150,000,000
Contract termination loss		221,000,000
Contract termination loss net of tax		165,000,000
Maximum
Schedule of Equity Method Investments [Line Items]
Equity in earnings(losses) on investments								$ 1,000,000
Maximum | Atlantic Coast Pipeline | DETI
Schedule of Equity Method Investments [Line Items]
Other receivables		1,000,000			$ 1,000,000			1,000,000					7,000,000
Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Net income (loss) from discontinued operations including noncontrolling interest								(2,300,000,000)	$ 84,000,000
Pivotal LNG | Dominion Energy Gas Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage acquired												100.00%
Pivotal LNG | JAX LNG LLC
Schedule of Equity Method Investments [Line Items]
Percentage of interest held												50.00%
Finite Lived Equity Method Investment Basis Difference
Schedule of Equity Method Investments [Line Items]
Equity method investment goodwill		(46,000,000)			(46,000,000)			(46,000,000)					(46,000,000)
Trading Securities
Schedule of Equity Method Investments [Line Items]
Rabbi trust securities		$ 132,000,000			$ 132,000,000			$ 132,000,000					$ 120,000,000

[1] Includes income tax expense (benefit) of $(10) million and $136 million for the three months ended September 30, 2020 and 2019, respectively and $(572) million and $47 million for the nine months ended September 30, 2020 and 2019, respectively.

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

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

[4] In October 2020, the joint revolving credit facility was amended to remove Dominion Energy Gas as a co-borrower.

[5] This credit facility matures in March 2023 and can be used by the borrowers under the credit facility to support bank borrowings and the issuance of commercial paper, as well as to support up to a combined $2.0 billion of letters of credit.

[6] Excludes Dominion Energy's guarantees for the new corporate office properties discussed in Note 15 to the Consolidated Financial Statements in the Companies’ Annual Report on Form 10-K for the year ended December 31, 2019 and in Note 14 in this report.