Investments (Portion of Unrealized Gains and Losses Relates to Equity Securities) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-Sale [Line Items]
Net gains (losses) recognized during the period		$ 811	$ (848)	$ 1,072
Less: Net (gains) losses recognized during the period on securities sold during the period		(7)	8	(346)
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	804	(840)	726
Virginia Electric and Power Company
Debt Securities, Available-for-Sale [Line Items]
Net gains (losses) recognized during the period		420	(436)	552
Less: Net (gains) losses recognized during the period on securities sold during the period		7	(7)	(190)
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	$ 427	$ (443)	$ 362

[1] Included in other income and the nuclear decommissioning trust regulatory liability as discussed in Note 2.