Investments (Selected Information Regarding Equity and Fixed Income Securities) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		$ 3,985	$ 4,278	$ 1,712
Realized gains	[1]	441	340	195
Realized losses	[1]	91	297	96
Virginia Electric and Power Company
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		1,791	884	858
Realized gains	[1]	228	88	58
Realized losses	[1]	$ 35	$ 68	$ 22

[1] Includes realized gains and losses recorded to the nuclear decommissioning trust regulatory liability as discussed in Note 2.