Accumulated Other Comprehensive Income (Schedule of Changes in AOCI by Component Net of Tax) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[1]			$ 17,142
Total other comprehensive income (loss)		$ 13	$ 53	145	$ 117
Cumulative-effect of changes in accounting principles				6
Ending balance		18,064		18,064
Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[2]			12,224
Total other comprehensive income (loss)			1	5	5
Cumulative-effect of changes in accounting principles				3
Ending balance		12,497		12,497
Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss)		(5)	1	6	3
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		(248)	(260)	(302)	(280)
Other comprehensive income before reclassifications: gains (losses)		(33)	28	78	71
Amounts reclassified from AOCI: (gains) losses	[3]	33	(18)	41	(41)
Net current period other comprehensive income (loss)			10	119	30
Cumulative-effect of changes in accounting principles				(64)
Less other comprehensive income attributable to noncontrolling interest				1
Ending balance		(248)	(250)	(248)	(250)
Deferred Gains and Losses on Derivatives-Hedging Activities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(10)	(8)	(12)	(8)
Other comprehensive income before reclassifications: gains (losses)		2	(3)	7	(3)
Amounts reclassified from AOCI: (gains) losses	[3]		1		1
Total other comprehensive income (loss)		2	(2)	7	(2)
Cumulative-effect of changes in accounting principles				(3)
Ending balance		(8)	(10)	(8)	(10)
Deferred Gains and Losses on Derivatives-Hedging Activities | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(18)	(22)	(23)	(24)
Other comprehensive income before reclassifications: gains (losses)		(20)	11	(7)	2
Amounts reclassified from AOCI: (gains) losses	[3]	14	(12)	11	(1)
Total other comprehensive income (loss)		(6)	(1)	4	1
Cumulative-effect of changes in accounting principles				(5)
Ending balance		(24)	(23)	(24)	(23)
Unrealized Gains and Losses on Investment Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		3	599	747	569
Other comprehensive income before reclassifications: gains (losses)		(5)	35	(18)	93
Amounts reclassified from AOCI: (gains) losses	[3]		(4)	1	(32)
Net current period other comprehensive income (loss)		(5)	31	(17)	61
Cumulative-effect of changes in accounting principles				(732)
Ending balance		(2)	630	(2)	630
Unrealized Gains and Losses on Investment Securities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		1	58	74	54
Other comprehensive income before reclassifications: gains (losses)		(2)	4	(2)	11
Amounts reclassified from AOCI: (gains) losses	[3]		(1)		(4)
Total other comprehensive income (loss)		(2)	3	(2)	7
Cumulative-effect of changes in accounting principles				(73)
Ending balance		(1)	61	(1)	61
Unrecognized Pension and Other Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(1,303)	(1,069)	(1,101)	(1,082)
Amounts reclassified from AOCI: (gains) losses	[3]	17	11	42	24
Net current period other comprehensive income (loss)		17	11	42	24
Cumulative-effect of changes in accounting principles				(227)
Ending balance		(1,286)	(1,058)	(1,286)	(1,058)
Unrecognized Pension and Other Postretirement Benefit Costs | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(95)	(99)	(75)	(99)
Other comprehensive income before reclassifications: gains (losses)		0	0	0	0
Amounts reclassified from AOCI: (gains) losses	[3]	1	2	2	2
Total other comprehensive income (loss)		1	2	2	2
Cumulative-effect of changes in accounting principles				(21)
Ending balance		(94)	(97)	(94)	(97)
Other Comprehensive Loss From Equity Method Investee
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(3)	(5)	(3)	(6)
Other comprehensive income before reclassifications: gains (losses)		1	1	1	2
Net current period other comprehensive income (loss)		1	1	1	2
Ending balance		(2)	(4)	(2)	(4)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(1,551)	(735)	(659)	(799)
Other comprehensive income before reclassifications: gains (losses)		(37)	64	61	166
Amounts reclassified from AOCI: (gains) losses	[3]	50	(11)	84	(49)
Total other comprehensive income (loss)				144	117
Net current period other comprehensive income (loss)		13	53	145	117
Cumulative-effect of changes in accounting principles				(1,023)
Less other comprehensive income attributable to noncontrolling interest				1
Ending balance		(1,538)	(682)	(1,538)	(682)
Accumulated Other Comprehensive Income (Loss) | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(9)	50	62	46
Other comprehensive income before reclassifications: gains (losses)			1	5	8
Amounts reclassified from AOCI: (gains) losses	[3]				(3)
Total other comprehensive income (loss)			1	5	5
Cumulative-effect of changes in accounting principles				(76)
Ending balance		(9)	51	(9)	51
Accumulated Other Comprehensive Income (Loss) | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(113)	(121)	(98)	(123)
Other comprehensive income before reclassifications: gains (losses)		(20)	11	(7)	2
Amounts reclassified from AOCI: (gains) losses	[3]	15	(10)	13	1
Total other comprehensive income (loss)		(5)	1	6	3
Cumulative-effect of changes in accounting principles				(26)
Ending balance		$ (118)	$ (120)	$ (118)	$ (120)

[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.