Equity (Schedule of Changes in AOCI by Component Net of Tax) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		$ 31,994
Total other comprehensive loss		76	$ (93)	$ (17)
Ending balance		26,117	31,994
Virginia Electric and Power Company
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		13,989	13,047	12,224
Total other comprehensive loss		(23)	(17)	2
Ending balance		14,557	13,989	13,047
Deferred Gains and Losses on Derivatives-Hedging Activities
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		(407)	(235)
Other comprehensive income before reclassifications: gains (losses)		(239)	(110)
Amounts reclassified from AOCI: (gains) losses	[1]	227	(62)
Total other comprehensive loss		(12)	(172)
Ending balance		(419)	(407)	(235)
Deferred Gains and Losses on Derivatives-Hedging Activities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		(34)	(13)
Other comprehensive income before reclassifications: gains (losses)		(28)	(22)
Amounts reclassified from AOCI: (gains) losses	[1]	2	1
Total other comprehensive loss		(26)	(21)
Ending balance		(60)	(34)	(13)
Unrealized Gains and Losses on Investment Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		37	2
Other comprehensive income before reclassifications: gains (losses)		43	39
Amounts reclassified from AOCI: (gains) losses	[1]	(18)	(4)
Total other comprehensive loss		25	35
Ending balance		62	37	2
Unrealized Gains and Losses on Investment Securities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		5	1
Other comprehensive income before reclassifications: gains (losses)		6	5
Amounts reclassified from AOCI: (gains) losses	[1]	(3)	(1)
Total other comprehensive loss		3	4
Ending balance		8	5	1
Unrecognized Pension and Other Postretirement Benefit Costs
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		(1,421)	(1,465)
Other comprehensive income before reclassifications: gains (losses)		25	(22)
Amounts reclassified from AOCI: (gains) losses	[1]	37	66
Total other comprehensive loss		62	44
Ending balance		(1,359)	(1,421)	(1,465)
Other Comprehensive Loss From Equity Method Investees
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		(2)	(2)
Other comprehensive income before reclassifications: gains (losses)		1
Total other comprehensive loss		1
Ending balance		(1)	(2)	(2)
AOCI
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		(1,793)	(1,700)
Other comprehensive income before reclassifications: gains (losses)		(170)	(93)
Amounts reclassified from AOCI: (gains) losses	[1]	246
Total other comprehensive loss		76	(93)	(18)
Ending balance		(1,717)	(1,793)	(1,700)
AOCI | Virginia Electric and Power Company
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		(29)	(12)	62
Other comprehensive income before reclassifications: gains (losses)		(22)	(17)
Amounts reclassified from AOCI: (gains) losses	[1]	(1)
Total other comprehensive loss		(23)	(17)	2
Ending balance		$ (52)	$ (29)	$ (12)

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