Investments (Portion of Unrealized Gains and Losses Relates to Equity Securities) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Investment Holdings [Line Items]
Net gains (losses) recognized during the period		$ (712)	$ 352	$ (918)	$ 631
Less: Net (gains) losses recognized during the period on securities sold during the period		6	(134)	5	(312)
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	(706)	218	(913)	319
Virginia Electric and Power Company
Investment Holdings [Line Items]
Net gains (losses) recognized during the period		(361)	170	(463)	313
Less: Net (gains) losses recognized during the period on securities sold during the period			(85)	(4)	(173)
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	$ (361)	$ 85	$ (467)	$ 140

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