Long-Term and Short-Term Debt (Narrative) (Detail) - USD ($)		1 Months Ended		3 Months Ended		6 Months Ended
		Mar. 31, 2025	Jan. 31, 2025	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	May 31, 2025	Apr. 30, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Commercial paper borrowing limit		$ 1,800,000,000
Affiliated and related party payables and other				$ 132,000,000		$ 132,000,000				$ 201,000,000
Interest charges	[1]			70,000,000	$ 67,000,000	141,000,000	$ 134,000,000
Maximum [Member]
Debt Instrument [Line Items]
Short term commercial paper maturity period		1 year
Genco
Debt Instrument [Line Items]
Commercial paper borrowing limit		$ 300,000,000
Genco | Maximum [Member]
Debt Instrument [Line Items]
Short term commercial paper maturity period		1 year
DESC | First mortgage bonds
Debt Instrument [Line Items]
Debt instrument, face amount			$ 450,000,000
Interest rate percentage			5.30%
Debt Instrument, Maturity Year			2035
Dominion Energy
Debt Instrument [Line Items]
Affiliated and related party payables and other				672,000,000		672,000,000				942,000,000
Interest charges				11,000,000	$ 12,000,000	22,000,000	$ 22,000,000
Inter company credit facility maximum capacity				900,000,000		900,000,000
Dominion Energy | Genco
Debt Instrument [Line Items]
Inter company credit facility maximum capacity				300,000,000		300,000,000		$ 300,000,000	$ 200,000,000
Dominion Energy | Fuel company
Debt Instrument [Line Items]
Inter company credit facility maximum capacity				400,000,000		400,000,000
Joint Revolving Credit Facility
Debt Instrument [Line Items]
Maximum Facility Sub-Limit	[2]			1,000,000,000		1,000,000,000
Joint Revolving Credit Facility | Commercial Paper
Debt Instrument [Line Items]
Debt instrument, face amount				239,000,000		239,000,000
Joint Revolving Credit Facility | Dominion Energy
Debt Instrument [Line Items]
Maximum Facility Sub-Limit									$ 7,000,000,000
Industrial Revenue Bonds
Debt Instrument [Line Items]
Debt instrument, face amount				68,000,000		68,000,000				$ 68,000,000
Intercompany Credit Facility
Debt Instrument [Line Items]
Line of credit, outstanding				353,000,000		353,000,000
Intercompany Credit Facility | Genco
Debt Instrument [Line Items]
Line of credit, outstanding				59,000,000		59,000,000
Letter of Credit
Debt Instrument [Line Items]
Maximum Facility Sub-Limit				$ 3,000,000,000		$ 3,000,000,000

[1] The significant expense categories and amounts in the segment information presented above align with the segment-level information that is regularly provided to DESC’s CODM.

[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 and Virginia Power. 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 June 30, 2025, the sub-limit for DESC was $1.0 billion, which was increased from $500 million in April 2025. In July 2025, the sub-limit was decreased to $900 million. If DESC has liquidity needs in excess of its sub-limit, the sub-limit may be changed provided that it does not exceed $1.0 billion or such needs may be satisfied through short-term borrowings from Dominion Energy. This credit facility matures in April 2030, with the potential to be extended by the borrowers to April 2032. The credit facility can be used to support bank borrowings and the issuance of commercial paper, as well as to support up to $3.0 billion (or the sub-limit, whichever is less) of letters of credit.