Leases (Summary of Total Lease Cost) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Finance lease cost:
Finance lease cost, Amortization	$ 40	$ 33	$ 20
Finance lease cost, Interest	(3)		4
Operating lease cost	66	68	79
Short-term lease cost	32	20	26
Variable lease cost	5	8	5
Total lease cost	140	129	134
Virginia Electric and Power Company
Finance lease cost:
Finance lease cost, Amortization	12	7	3
Finance lease cost, Interest	1	1
Operating lease cost	30	36	41
Short-term lease cost	19	12	13
Variable lease cost	1	4	2
Total lease cost	$ 63	$ 60	$ 59