Investments (Selected Information Regarding Equity and Fixed Income Securities) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		$ 605	$ 614	$ 2,686	$ 3,324
Realized gains	[1]	17	25	132	405
Realized losses	[1]	50	7	247	81
Virginia Electric and Power Company
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		425	216	1,289	1,465
Realized gains	[1]	14	17	40	213
Realized losses	[1]	$ 33	$ 2	$ 85	$ 28

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