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, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Total Derivative-Hedging Activities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	$ 61	$ 58	$ 68	$ 73
Total Derivative-Hedging Activities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	(7)	(10)	(7)	(5)
Investment Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	0	5	6	(2)
Investment Securities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	0		1
Pension and Other Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount of tax	$ (9)	$ (9)	$ (10)	$ (14)