Accumulated Other Comprehensive Income (Schedule of Changes in AOCI by Component Net of Tax) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[1]	$ 17,142
Cumulative-effect of changes in accounting principles		6
Ending balance		17,689
Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[2]	12,224
Cumulative-effect of changes in accounting principles		3
Ending balance		12,262
Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative-effect of changes in accounting principles		3
Deferred Gains and Losses on Derivatives-Hedging Activities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(302)	$ (280)
Other comprehensive income before reclassifications: gains (losses)		111	43
Amounts reclassified from AOCI: (gains) losses	[3]	8	(23)
Net current period other comprehensive income (loss)		119	20
Cumulative-effect of changes in accounting principles		(64)
Less other comprehensive income attributable to noncontrolling interest		1
Ending balance		(248)	(260)
Deferred Gains and Losses on Derivatives-Hedging Activities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(12)	(8)
Other comprehensive income before reclassifications: gains (losses)		5
Net current period other comprehensive income (loss)		5
Cumulative-effect of changes in accounting principles		(3)
Ending balance		(10)	(8)
Deferred Gains and Losses on Derivatives-Hedging Activities | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(23)	(24)
Other comprehensive income before reclassifications: gains (losses)		13	(9)
Amounts reclassified from AOCI: (gains) losses	[3]	(3)	11
Net current period other comprehensive income (loss)		10	2
Cumulative-effect of changes in accounting principles		(5)	0
Ending balance		(18)	(22)
Unrealized Gains and Losses on Investment Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		747	569
Other comprehensive income before reclassifications: gains (losses)		(13)	58
Amounts reclassified from AOCI: (gains) losses	[3]	1	(28)
Net current period other comprehensive income (loss)		(12)	30
Cumulative-effect of changes in accounting principles		(732)
Ending balance		3	599
Unrealized Gains and Losses on Investment Securities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		74	54
Other comprehensive income before reclassifications: gains (losses)			7
Amounts reclassified from AOCI: (gains) losses	[3]		(3)
Net current period other comprehensive income (loss)			4
Cumulative-effect of changes in accounting principles		(73)
Ending balance		1	58
Unrecognized Pension and Other Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(1,101)	(1,082)
Amounts reclassified from AOCI: (gains) losses	[3]	25	13
Net current period other comprehensive income (loss)		25	13
Cumulative-effect of changes in accounting principles		(227)
Ending balance		(1,303)	(1,069)
Unrecognized Pension and Other Postretirement Benefit Costs | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(75)	(99)
Other comprehensive income before reclassifications: gains (losses)		0	0
Amounts reclassified from AOCI: (gains) losses	[3]	1	0
Net current period other comprehensive income (loss)		1	0
Cumulative-effect of changes in accounting principles		(21)	0
Ending balance		(95)	(99)
Other Comprehensive Loss From Equity Method Investee
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(3)	(6)
Other comprehensive income before reclassifications: gains (losses)			1
Net current period other comprehensive income (loss)			1
Ending balance		(3)	(5)
Total
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(659)	(799)
Other comprehensive income before reclassifications: gains (losses)		98	102
Amounts reclassified from AOCI: (gains) losses	[3]	34	(38)
Net current period other comprehensive income (loss)		132	64
Cumulative-effect of changes in accounting principles		(1,023)
Less other comprehensive income attributable to noncontrolling interest		1
Ending balance		(1,551)	(735)
Total | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		62	46
Other comprehensive income before reclassifications: gains (losses)		5	7
Amounts reclassified from AOCI: (gains) losses	[3]		(3)
Net current period other comprehensive income (loss)		5	4
Cumulative-effect of changes in accounting principles		(76)
Ending balance		(9)	50
Total | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(98)	(123)
Other comprehensive income before reclassifications: gains (losses)		13	(9)
Amounts reclassified from AOCI: (gains) losses	[3]	(2)	11
Net current period other comprehensive income (loss)		11	2
Cumulative-effect of changes in accounting principles		(26)	0
Ending balance		$ (113)	$ (121)

[1] Dominion Energy’s Consolidated Balance Sheet at December 31, 2017 has been derived from the audited Consolidated Balance Sheet at that date.

[2] Virginia Power’s Consolidated Balance Sheet at December 31, 2017 has been derived from the audited Consolidated Balance Sheet at that date.

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