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, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Total Derivative-Hedging Activities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	$ 68	$ 73	$ 83	$ 83
Total Derivative-Hedging Activities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	(7)	(5)	(2)	(5)
Investment Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	6	(2)	6	13
Investment Securities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	1	0	1	2
Pension and Other Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	538	456	449	445
Equity Method Investees
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	$ 0	$ 0	$ 0	$ 1