Investments (Selected Information Regarding Equity and Fixed Income Securities) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		$ 869	$ 605	$ 2,007	$ 2,686
Realized gains	[1]	5	17	48	132
Realized losses	[1]	33	50	110	247
Virginia Electric and Power Company
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		535	425	1,254	1,289
Realized gains	[1]	4	14	29	40
Realized losses	[1]	$ 16	$ 33	$ 61	$ 85

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