Investments (Selected Information Regarding Equity and Fixed Income Securities) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		$ 1,267	$ 945	$ 2,081	$ 2,710
Realized gains	[1]	75	148	115	380
Realized losses	[1]	143	15	197	74
Virginia Electric and Power Company
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales		472	460	864	1,249
Realized gains	[1]	10	90	26	196
Realized losses	[1]	$ 33	$ 3	$ 52	$ 26

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