Long-Term and Short-Term Debt (Narrative) (Detail) - USD ($)			1 Months Ended		3 Months Ended		9 Months Ended
		Jan. 31, 2020	Mar. 31, 2020	Apr. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Debt Instrument [Line Items]
Commercial paper borrowing limit			$ 2,200,000,000
Commercial paper maturity period			2021-03
Short Term Borrowing Maturity Period		2 years
Interest charges	[1]				$ 57,000,000	$ 66,000,000	$ 173,000,000	$ 202,000,000
Interest income from money pool transactions					1,000,000	1,000,000	2,000,000	7,000,000
Interest expense from money pool transactions					1,000,000	1,000,000	2,000,000	7,000,000
Maximum [Member]
Debt Instrument [Line Items]
Short term commercial paper maturity period			1 year
Genco
Debt Instrument [Line Items]
Commercial paper borrowing limit			$ 200,000,000
Investments due from affiliates					9,000,000		9,000,000		$ 9,000,000
Genco | Maximum [Member]
Debt Instrument [Line Items]
Short term commercial paper maturity period			1 year
Fuel Company
Debt Instrument [Line Items]
Money pool borrowings due to affiliates					215,000,000		215,000,000		219,000,000
Dominion Energy
Debt Instrument [Line Items]
Short-term borrowings outstanding, maximum				$ 900,000,000
Short-term borrowings outstanding					229,000,000		229,000,000		$ 355,000,000
Interest charges					2,000,000	$ 1,000,000	7,000,000	$ 1,000,000
Joint Revolving Credit Facility
Debt Instrument [Line Items]
Facility limit	[2],[3]				1,000,000,000		1,000,000,000
Joint Revolving Credit Facility | Dominion Energy
Debt Instrument [Line Items]
Facility limit					6,000,000,000.0		6,000,000,000.0
Letter of Credit
Debt Instrument [Line Items]
Facility limit					1,000,000,000.0		1,000,000,000.0
Debt instrument, face amount					$ 68,000,000		$ 68,000,000

[1] See Note 14 for amounts attributable to affiliates.

[2] A maximum of $1.0 billion of the facility is available to DESC, assuming adequate capacity is available after giving effect to uses by co-borrowers Dominion Energy, Virginia Power and Questar Gas. The sub-limit for DESC is set within the facility limit but can be changed at the option of the co-borrowers multiple times per year. At September 30, 2020, the sub-limit for DESC was $500 million. If DESC has liquidity needs in excess of its sub-limit, the sub-limit may be changed or such needs may be satisfied through short-term borrowings from DESC's parent or from Dominion Energy. This credit facility matures in March 2023 and can be used to support bank borrowings and the issuance of commercial paper, as well as to support up to $1.0 billion (or the sub-limit, whichever is less) of letters of credit

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