Accumulated Other Comprehensive Income (Schedule of Reclassifications out of AOCI by Component Net of Tax) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue		$ (3,870)	$ (3,938)
Interest and related charges		53	432
Other income (expense)		(367)	454
Income tax expense (benefit)		212	(50)
Income (loss) including noncontrolling interests, net of tax		(980)	468
Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue	[1]	(1,830)	(1,930)
Interest and related charges	[1]	136	126
Other income (expense)		(32)	52
Income from operations before income tax expense		(444)	311
Income tax expense (benefit)		70	(31)
Deferred (Gains) and Losses on Derivatives-Hedging Activities | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income from operations before income tax expense		17	29
Income tax expense (benefit)		4	(7)
Income (loss) including noncontrolling interests, net of tax		13	22
Deferred (Gains) and Losses on Derivatives-Hedging Activities | Amounts Reclassified From AOCI | Commodity contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue			(6)
Purchased gas		1	3
Discontinued operations			(1)
Deferred (Gains) and Losses on Derivatives-Hedging Activities | Amounts Reclassified From AOCI | Interest rate contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and related charges		16	25
Discontinued operations			2
Deferred (Gains) and Losses on Derivatives-Hedging Activities | Amounts Reclassified From AOCI | Foreign currency
Accumulated Other Comprehensive Income (Loss) [Line Items]
Discontinued operations			6
Unrealized (gains) and losses on investment securities: | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Realized (gains) losses on sale of securities		1	(13)
Income from operations before income tax expense		1	(13)
Income tax expense (benefit)			4
Income (loss) including noncontrolling interests, net of tax		1	(9)
Unrealized (gains) and losses on investment securities: | Amounts Reclassified From AOCI | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Realized (gains) losses on sale of securities		1	2
Income from operations before income tax expense		1	2
Income tax expense (benefit)			(1)
Income (loss) including noncontrolling interests, net of tax		1	1
Amortization of prior-service costs (credits) | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income (expense)		(5)	(6)
Amortization of actuarial losses | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income (expense)		30	30
Unrecognized pension and other postretirement benefit costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrecognized pension and other postretirement benefit costs, before tax		25	24
Unrecognized pension and other postretirement benefit costs, income tax expense (benefit)		(7)	(5)
Unrecognized pension and other postretirement benefit costs, net of tax		18	19
Deferred Gains and Losses on Derivatives-Hedging Activities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrecognized pension and other postretirement benefit costs, net of tax	[2]	13	$ 22
Deferred Gains and Losses on Derivatives-Hedging Activities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrecognized pension and other postretirement benefit costs, net of tax	[3]	1
Deferred Gains and Losses on Derivatives-Hedging Activities | Amounts Reclassified From AOCI | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income from operations before income tax expense		1
Income (loss) including noncontrolling interests, net of tax		1
Deferred Gains and Losses on Derivatives-Hedging Activities | Amounts Reclassified From AOCI | Interest rate contracts | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and related charges		$ 1

[1] See Note 19 for amounts attributable to affiliates.

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

[3] See table below for details about these reclassifications