Long-Term and Short-Term Debt (Schedule of Line of Credit Facilities) (Detail) - Joint Revolving Credit Facility	Jun. 30, 2025 USD ($)	[1]
Debt Instrument [Line Items]
Maximum Facility Sub-Limit	$ 1,000,000,000
Outstanding Commercial Paper	239,000,000
Outstanding Letters of Credit	$ 0

[1] 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.