Asset Retirement Obligations (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018
Asset Retirement Obligations [Line Items]
Nuclear decommissioning trust funds	$ 6,192		$ 4,938
Asset Retirement Obligation, Liabilities Incurred	2,413	[1]	20
Virginia Electric and Power Company
Asset Retirement Obligations [Line Items]
Nuclear decommissioning trust funds	2,881		2,369
Asset Retirement Obligation, Liabilities Incurred	2,408	[1]	14
D Virginia Electric And Power Company [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Liabilities Incurred	1,700		1,600
D Virginia Electric And Power Company [Member] | Future Decommissioning Of Nuclear Facilities [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Liabilities Incurred	800		$ 900
D Virginia Electric And Power Company [Member] | D Cost Of Landfills And Beneficial Reuse [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Liabilities Incurred	$ 2,600

[1] Reflects future ash pond and landfill closure costs at certain utility generation facilities. See Note 23 for further information.