Investments (Portion of Unrealized Gains and Losses Relates to Equity Securities) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Investment Holdings [Line Items]
Net gains (losses) recognized during the period		$ (898)	$ 414
Less: Net (gains) losses recognized during the period on securities sold during the period		14	(19)
Unrealized gains (losses) recognized during the period on securities still held at March 31, 2020 and 2019	[1]	(884)	395
Virginia Electric and Power Company
Investment Holdings [Line Items]
Net gains (losses) recognized during the period		(423)	186
Less: Net (gains) losses recognized during the period on securities sold during the period		6	(1)
Unrealized gains (losses) recognized during the period on securities still held at March 31, 2020 and 2019	[1]	$ (417)	$ 185

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