Investments (Portion of Unrealized Gains and Losses Relates to Equity Securities) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Debt Securities, Available-for-Sale [Line Items]
Net gains (losses) recognized during the period		$ (150)	$ (205)	$ 370	$ (1,123)
Less: Net (gains) losses recognized during the period on securities sold during the period		1	(2)	4	3
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	(149)	(207)	374	(1,120)
Virginia Electric and Power Company
Debt Securities, Available-for-Sale [Line Items]
Net gains (losses) recognized during the period		(80)	(118)	189	(581)
Less: Net (gains) losses recognized during the period on securities sold during the period		(1)	(4)	2	(8)
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	$ (81)	$ (122)	$ 191	$ (589)

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