Investments (Portion of Unrealized Gains and Losses Relates to Equity Securities) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Investment Holdings [Line Items]
Net gains (losses) recognized during the period		$ (205)	$ (15)	$ (1,123)	$ 616
Less: Net (gains) losses recognized during the period on securities sold during the period		(2)	(11)	3	(323)
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	(207)	(26)	(1,120)	293
Virginia Electric and Power Company
Investment Holdings [Line Items]
Net gains (losses) recognized during the period		(118)	6	(581)	319
Less: Net (gains) losses recognized during the period on securities sold during the period		(4)	(9)	(8)	(182)
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	$ (122)	$ (3)	$ (589)	$ 137

[1] Included in other income and the nuclear decommissioning trust regulatory liability.