Investments (Selected Information Regarding Equity and Fixed Income Securities) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		$ 1,058	$ 376	$ 1,660	$ 882
Realized gains	[1]	74	56	140	99
Realized losses	[1]	61	27	130	50
Virginia Electric and Power Company
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		236	194	530	447
Realized gains	[1]	24	15	55	25
Realized losses	[1]	$ 17	$ 3	$ 48	$ 12

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