Investments (Selected Information Regarding Equity and Fixed Income Securities) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		$ 945	$ 1,058	$ 2,710	$ 1,660
Realized gains	[1]	148	74	380	140
Realized losses	[1]	15	61	74	130
Virginia Electric and Power Company
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		460	236	1,249	530
Realized gains	[1]	90	24	196	55
Realized losses	[1]	$ 3	$ 17	$ 26	$ 48

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