Related-Party Transactions (Narrative) (Detail) - USD ($)	1 Months Ended		12 Months Ended
	Sep. 30, 2020	Aug. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Derivative Asset			$ 397,000,000	$ 93,000,000
Derivative Liabilities			486,000,000	$ 740,000,000
Issuance of common stock (in shares)	4,100,000	18,500,000		6,100,000
Virginia Electric and Power Company
Related Party Transaction [Line Items]
Derivative Asset			181,000,000	$ 24,000,000
Derivative Liabilities			405,000,000	466,000,000
Payable to affiliates			380,000,000	107,000,000
Outstanding borrowings, net of repayments, under money pool for non-regulated subsidiaries			$ 0	$ 0
Issuance of common stock (in shares)			0	0	0
Virginia Electric and Power Company | Pension Benefits | Amounts Associated With Dominion Pension Plan
Related Party Transaction [Line Items]
Amounts due to Dominion, noncurrent			$ 436,000,000	$ 782,000,000
Virginia Electric and Power Company | Medical Coverage for Local retirees | Amounts Associated with the Dominion Retiree Health and Welfare Plan
Related Party Transaction [Line Items]
Amounts due from Dominion, noncurrent			354,000,000	287,000,000
Virginia Electric and Power Company | Affiliated Entity
Related Party Transaction [Line Items]
Derivative Asset			3,000,000	3,000,000
Derivative Liabilities			22,000,000	53,000,000
Virginia Electric and Power Company | Principal Owner | Short-Term Borrowing Arrangements
Related Party Transaction [Line Items]
Payable to affiliates			$ 380,000,000	$ 107,000,000
Weighted- average interest rate percentage			0.30%	3.22%