Accumulated Other Comprehensive Income (Schedule of Reclassifications out of AOCI by Component Net of Tax) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue		$ (3,607)	$ (3,782)	$ (10,651)	$ (10,506)
Interest and related charges		306	370	1,136	1,133
Other income		(281)	(129)	(327)	(526)
Income tax expense (benefit)		(110)	(84)	(123)	161
Income (loss) including noncontrolling interests, net of tax		(112)	(947)	(513)	160
Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue	[1]	(2,248)	(2,264)	(5,983)	(6,167)
Interest and related charges	[1]	135	138	398	408
Other income		(34)	(15)	(34)	(68)
Income from operations before income tax expense		(586)	(697)	(825)	(840)
Income tax expense (benefit)		111	95	140	118
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		251	(7)	287	(77)
Income tax expense (benefit)		63	1	(72)	19
Income (loss) including noncontrolling interests, net of tax		188	(6)	215	(58)
Deferred (Gains) and Losses on Derivatives-Hedging Activities | Amounts Reclassified From AOCI | Commodity contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue		(8)	(34)	(22)	(123)
Purchased gas			2	3	1
Discontinued operations			(1)	(2)	(4)
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		(23)	12	66	35
Discontinued operations		230	2	236	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	12	6	14
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		(3)	(5)	(21)	(6)
Income from operations before income tax expense		(3)	(5)	(21)	(6)
Income tax expense (benefit)		2	1	6	1
Income (loss) including noncontrolling interests, net of tax		(1)	(4)	(15)	(5)
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)		(3)
Income from operations before income tax expense		(1)		(3)
Income tax expense (benefit)		0		1
Income (loss) including noncontrolling interests, net of tax		(1)		(2)
Amortization of prior-service costs (credits) | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income		(5)	(5)	(16)	(18)
Amortization of actuarial losses | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income		36	31	97	85
Unrecognized pension and other postretirement benefit costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrecognized pension and other postretirement benefit costs, before tax		31	26	81	67
Unrecognized pension and other postretirement benefit costs, income tax expense (benefit)		(8)	(6)	(21)	(17)
Unrecognized pension and other postretirement benefit costs, net of tax		23	20	60	50
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]	188	(6)	215	(58)
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	$ 0	1	$ 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		2
Income tax expense (benefit)		0		(1)
Income (loss) including noncontrolling interests, net of tax		1		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		$ 2

[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. Virginia Power’s reclassifications out of AOCI were immaterial for both the three and nine months ended September 30, 2019