Leases (Summary of Total Lease Cost) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Finance lease cost:
Finance lease cost, Amortization	$ 20
Finance lease cost, Interest	4
Operating lease cost	87
Short-term lease cost	30
Variable lease cost	6
Total lease cost	147
Virginia Electric and Power Company
Finance lease cost:
Operating lease cost	41
Short-term lease cost	13
Variable lease cost	2
Total lease cost	56
Dominion Energy Gas Holdings, LLC
Finance lease cost:
Operating lease cost	7
Short-term lease cost	7
Total lease cost	$ 14