Long-Term and Short-Term Debt (Schedule of Line of Credit Facilities) (Parenthetical) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	[1],[2]
Joint Revolving Credit Facility
Debt Instrument [Line Items]
Facility limit	$ 1,000,000,000	$ 1,000,000,000
Line of credit facility maturity date	2023-03
Line of Credit Facility
Debt Instrument [Line Items]
Facility limit	$ 500,000,000
Letter of Credit
Debt Instrument [Line Items]
Facility limit	$ 1,000,000,000.0

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

[2] A maximum of $1.0 billion of the facility is available to DESC, less any amounts outstanding to co-borrowers. A 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 December 31, 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.