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	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Total Derivative-Hedging Activities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	$ 87	$ 94	$ 119	$ 121	$ 125	$ 141
Total Derivative-Hedging Activities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	(4)		16	14	14	21
Investment Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	23	14	(10)	(11)	(12)	(21)
Investment Securities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	4	3	(2)	(2)	(2)	(3)
Pension and Other Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	367	376	396	448	$ 455	$ 478
Equity Method Investees
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	$ 1	$ 1	$ 1	$ 1