Related-Party Transactions (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Related Party Transaction [Line Items]
Capital expenditures	$ 1,462	$ 1,002
Virginia Electric and Power Company
Related Party Transaction [Line Items]
Capital expenditures	764	563
Virginia Electric and Power Company | Services provided by affiliates | Affiliated Entity
Related Party Transaction [Line Items]
Capital expenditures	34	33
Dominion Energy Gas Holdings, LLC
Related Party Transaction [Line Items]
Capital expenditures	76	150
Dominion Energy Gas Holdings, LLC | Services provided by affiliates | Affiliated Entity
Related Party Transaction [Line Items]
Capital expenditures	$ 3	$ 6