Related-Party Transactions (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Virginia Electric and Power Company
Related Party Transaction [Line Items]
Capital expenditures			$ 1,474	$ 1,079
Virginia Electric and Power Company | Services provided by affiliates | Affiliated Entity
Related Party Transaction [Line Items]
Capital expenditures	$ 34	$ 34	68	67
Dominion Energy Gas Holdings, LLC
Related Party Transaction [Line Items]
Capital expenditures			147	341
Dominion Energy Gas Holdings, LLC | Services provided by affiliates | Affiliated Entity
Related Party Transaction [Line Items]
Capital expenditures	$ 4	$ 5	$ 7	$ 11