Long-Term and Short-Term Debt (Narrative) (Detail) - USD ($)		3 Months Ended		12 Months Ended
		Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Sep. 30, 2023
Debt Instrument [Line Items]
Commercial paper borrowing limit				$ 2,200,000,000
Affiliated and related party payables and other		$ 133,000,000		$ 166,000,000
Interest charges	[1]	67,000,000	$ 59,000,000
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
Genco | Maximum [Member]
Debt Instrument [Line Items]
Short term commercial paper maturity period				1 year
Dominion Energy
Debt Instrument [Line Items]
Affiliated and related party payables and other		672,000,000		$ 442,000,000
Interest charges		10,000,000	$ 13,000,000
Inter company credit facility maximum capacity		900,000,000
Dominion Energy | Genco
Debt Instrument [Line Items]
Inter company credit facility maximum capacity		200,000,000
Dominion Energy | Fuel company
Debt Instrument [Line Items]
Inter company credit facility maximum capacity		400,000,000
Joint Revolving Credit Facility
Debt Instrument [Line Items]
Maximum Facility Sub-Limit	[2]	1,000,000,000
Joint Revolving Credit Facility | Commercial Paper
Debt Instrument [Line Items]
Debt instrument, face amount		210,000,000
Joint Revolving Credit Facility | Dominion Energy
Debt Instrument [Line Items]
Maximum Facility Sub-Limit					$ 6,000,000,000
Industrial Revenue Bonds
Debt Instrument [Line Items]
Debt instrument, face amount		68,000,000		$ 68,000,000
Intercompany Credit Facility
Debt Instrument [Line Items]
Line of credit, outstanding		371,000,000
Intercompany Credit Facility | Genco
Debt Instrument [Line Items]
Line of credit, outstanding		$ 23,000,000

[1] See Note 12 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. 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 March 31, 2024, 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 intercompany borrowings from Dominion Energy. This credit facility matures in June 2026, with the potential to be extended by the borrowers to June 2028. The credit facility 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.