Investments (Portion of Unrealized Gains and Losses Relates to Equity Securities) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Investment Holdings [Line Items]
Net gains (losses) recognized during the period		$ (206)	$ 279
Less: Net (gains) losses recognized during the period on securities sold during the period		(1)	(178)
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	(207)	101
Virginia Electric and Power Company
Investment Holdings [Line Items]
Net gains (losses) recognized during the period		(102)	143
Less: Net (gains) losses recognized during the period on securities sold during the period		(4)	(88)
Unrealized gains (losses) recognized during the period on securities still held at period end	[1]	$ (106)	$ 55

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