Equity (Schedule of Reclassifications out of AOCI by Component Net of Tax) (Detail) - USD ($) $ in Millions			3 Months Ended								12 Months Ended
		Nov. 30, 2020	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Operating revenue			$ (3,521)	$ (3,607)	$ (3,106)	$ (3,938)	$ (3,895)	$ (3,782)	$ (3,443)	$ (3,281)	$ (14,172)		$ (14,401)		$ (11,199)
Interest and related charges											1,377		1,486		1,279
Income tax expense		$ 336									83		209		522
Income from continuing operations including noncontrolling interests			(815)	(112)	(869)	468	(820)	(947)	199	908	(1,328)		(660)		(2,097)
Other Income											(733)		(811)		(885)
Virginia Electric and Power Company
Accumulated Other Comprehensive Income Loss [Line Items]
Operating revenue			$ (1,780)	$ (2,248)	$ (1,805)	$ (1,930)	$ (1,941)	$ (2,264)	$ (1,938)	$ (1,965)	(7,763)	[1]	(8,108)	[1]	(7,619)	[1]
Interest and related charges	[1]										516		524		511
Income from operations before income tax expense											(1,250)		(1,413)		(1,582)
Income tax expense											229		264		300
Other Income											(80)		(98)		$ (22)
(Gains) Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income Loss [Line Items]
Unrecognized pension and other postretirement benefit costs, net of tax	[2]										227		(62)
(Gains) Losses on Cash Flow Hedges | Virginia Electric and Power Company
Accumulated Other Comprehensive Income Loss [Line Items]
Unrecognized pension and other postretirement benefit costs, net of tax	[2]										2		1
Amounts reclassified from AOCI | Deferred (Gains) and Losses on Derivatives-Hedging Activities
Accumulated Other Comprehensive Income Loss [Line Items]
Income from operations before income tax expense											302		(83)
Income tax expense											(75)		21
Income from continuing operations including noncontrolling interests											227		(62)
Amounts reclassified from AOCI | Deferred (Gains) and Losses on Derivatives-Hedging Activities | Commodity
Accumulated Other Comprehensive Income Loss [Line Items]
Operating revenue											(25)		(142)
Purchased gas											4		3
Discontinued operations											(2)		(4)
Amounts reclassified from AOCI | Deferred (Gains) and Losses on Derivatives-Hedging Activities | Interest rate
Accumulated Other Comprehensive Income Loss [Line Items]
Discontinued operations											236		5
Interest and related charges											83		49
Amounts reclassified from AOCI | Deferred (Gains) and Losses on Derivatives-Hedging Activities | Foreign currency contracts
Accumulated Other Comprehensive Income Loss [Line Items]
Discontinued operations											6		6
Amounts reclassified from AOCI | Unrealized (gains) and losses on investment securities
Accumulated Other Comprehensive Income Loss [Line Items]
Income from operations before income tax expense											(24)		(5)
Income tax expense											6		1
Income from continuing operations including noncontrolling interests											(18)		(4)
Realized (gain) loss on sale of securities											(24)		(5)
Amounts reclassified from AOCI | Unrealized (gains) and losses on investment securities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income Loss [Line Items]
Income from operations before income tax expense											(4)		(2)
Income tax expense											1		1
Income from continuing operations including noncontrolling interests											(3)		(1)
Realized (gain) loss on sale of securities											(4)		(2)
Amounts reclassified from AOCI | Amortization of prior-service costs (credits)
Accumulated Other Comprehensive Income Loss [Line Items]
Other Income											(84)		(24)
Amounts reclassified from AOCI | Amortization of actuarial losses
Accumulated Other Comprehensive Income Loss [Line Items]
Other Income											134		113
Amounts reclassified from AOCI | Unrecognized pension and other postretirement benefit costs
Accumulated Other Comprehensive Income Loss [Line Items]
Unrecognized pension and other postretirement benefit costs, before tax											50		89
Unrecognized pension and other postretirement benefit costs, income tax expense											(13)		(23)
Unrecognized pension and other postretirement benefit costs, net of tax											37		66
Amounts reclassified from AOCI | (Gains) Losses on Cash Flow Hedges | Virginia Electric and Power Company
Accumulated Other Comprehensive Income Loss [Line Items]
Income from operations before income tax expense											2		1
Income from continuing operations including noncontrolling interests											2		1
Amounts reclassified from AOCI | (Gains) Losses on Cash Flow Hedges | Interest rate | Virginia Electric and Power Company
Accumulated Other Comprehensive Income Loss [Line Items]
Interest and related charges											$ 2		$ 1

[1] See Note 25 for amounts attributable to affiliates.

[2] See table below for details about these reclassifications.