Investments (Portion of Unrealized Gains and Losses Relates to Equity Securities) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Net gains (losses) recognized during the period		$ 1,072	$ 512	$ 919
Less: Net gains recognized during the period on securities sold during the period		(346)	(16)	(80)
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	726	496	839
Virginia Electric and Power Company
Investment Holdings [Line Items]
Net gains (losses) recognized during the period		552	224	423
Less: Net gains recognized during the period on securities sold during the period		(190)	(6)	(20)
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	$ 362	$ 218	$ 403

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