Significant Accounting Policies (Schedule of Supplemental Cash Flow Information) (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Schedule Of Supplemental Cash Flow Information [Line Items]
Financing leases	$ 6	$ 2
Operating Leases	18	7
Virginia Electric and Power Company
Schedule Of Supplemental Cash Flow Information [Line Items]
Financing leases	4	$ 1
Operating Leases	$ 17