Asset Retirement Obligations (Changes to AROs) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019
Asset Retirement Obligations [Line Items]
AROs, Beginning balance		$ 5,184	[1]	$ 2,444
Obligations incurred during the period		67		2,413	[2]
AROs acquired in the SCANA Combination				577
Obligations settled during the period		(114)		(134)
Revisions in estimated cash flows		228	[3]	(324)	[4]
Accretion		218		208
AROs, Ending balance	[1]	5,583		5,184
Virginia Electric and Power Company
Asset Retirement Obligations [Line Items]
AROs, Beginning balance		3,581		1,445
Obligations incurred during the period		48		2,408	[2]
Obligations settled during the period		(85)		(81)
Revisions in estimated cash flows		139	[5]	(323)	[4]
Accretion		137		132
AROs, Ending balance		$ 3,820		$ 3,581

[1] Includes $394 million and $179 million reported in other current liabilities at December 31, 2019 and 2020, respectively.

[2] Reflects future ash pond and landfill closure costs at certain utility generation facilities. See discussion below.

[3] Reflects revisions to future ash pond and landfill closure costs at certain utility generation facilities, asbestos abatement costs associated with certain utility facilities and from the completion of a nuclear decommissioning cost study related to Summer.

[4] Reflects revisions to future ash pond and landfill closure costs at certain utility generation facilities as well as revisions for 20-year license extensions for regulated nuclear power stations in Virginia.

[5] Reflects revisions to future ash pond and landfill closure costs at certain utility generation facilities and asbestos abatement costs associated with certain utility facilities.