Accumulated Other Comprehensive Income (Loss) (Schedule of Changes in AOCI Net of Tax and Reclassifications out of AOCI by Component) (Parenthetical) (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Total Derivative-Hedging Activities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	$ 107	$ 119	$ 123	$ 141
Total Derivative-Hedging Activities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	9	16	10	21
Investment Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	8	(10)	(11)	(21)
Investment Securities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	1	(2)	(2)	(3)
Pension and Other Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	380	396	$ 468	$ 478
Equity Method Investees
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	$ 1	$ 1