Investments (Selected Information Regarding Equity and Fixed Income Securities) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		$ 814	$ 1,765
Realized gains	[1]	40	232
Realized losses	[1]	54	59
Virginia Electric and Power Company
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		392	789
Realized gains	[1]	16	106
Realized losses	[1]	$ 19	$ 23

[1] Includes realized gains and losses recorded to the nuclear decommissioning trust regulatory liability.