Accumulated Other Comprehensive Income (Loss) (Schedule of Reclassifications out of AOCI by Component Net of Tax) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue		$ (3,038)	$ (3,106)	$ (6,908)	$ (7,044)
Interest and related charges		518	398	571	830
Income tax expense (benefit)		(47)	37	165	(13)
Income (loss) including noncontrolling interests, net of tax		(269)	(869)	(1,249)	(401)
Other income (expense)		(312)	(498)	(599)	(41)
Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue	[1]	(1,741)	(1,805)	(3,571)	(3,735)
Interest and related charges	[1]	128	137	264	263
Income from operations before income tax expense		(483)	(550)	(927)	(239)
Income tax expense (benefit)		69	60	139	29
Other income (expense)		(40)	(52)	(72)
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		16	7	33	36
Income tax expense (benefit)		(4)	(2)	(8)	(9)
Income (loss) including noncontrolling interests, net of tax		12	5	25	27
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	1	(1)
Income tax expense (benefit)			(1)		(1)
Income (loss) including noncontrolling interests, net of tax				1
Deferred (Gains) and Losses on Derivatives-Hedging Activities | Amounts Reclassified From AOCI | Commodity contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue			(8)		(14)
Purchased gas				1	3
Discontinued operations			(1)		(2)
Deferred (Gains) and Losses on Derivatives-Hedging Activities | Amounts Reclassified From AOCI | Interest rate contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Discontinued operations			4		6
Interest and related charges		16	18	32	43
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	1
Deferred (Gains) and Losses on Derivatives-Hedging Activities | Amounts Reclassified From AOCI | Foreign Currency Contracts
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		(4)	(5)	(3)	(18)
Income from operations before income tax expense		(4)	(5)	(3)	(18)
Income tax expense (benefit)		1		1	4
Income (loss) including noncontrolling interests, net of tax		(3)	(5)	(2)	(14)
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)	(4)		(2)
Income from operations before income tax expense		(1)	(4)		(2)
Income tax expense (benefit)			2		1
Income (loss) including noncontrolling interests, net of tax		(1)	(2)		(1)
Amortization of prior-service costs (credits) | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income (expense)		(5)	(5)	(10)	(11)
Amortization of actuarial losses | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income (expense)		40	31	70	61
Unrecognized pension and other postretirement benefit costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrecognized pension and other postretirement benefit costs, before tax		35	26	60	50
Unrecognized pension and other postretirement benefit costs, income tax expense (benefit)		(9)	(8)	(16)	(13)
Unrecognized pension and other postretirement benefit costs, net of tax		$ 26	$ 18	$ 44	$ 37

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