Accumulated Other Comprehensive Income (Schedule of Changes in AOCI by Component Net of Tax) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[1]			$ 17,142
Total other comprehensive income (loss)		$ 18	$ 54	163	$ 171
Cumulative-effect of changes in accounting principles				6
Ending balance		18,470		18,470
Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[2]			12,224
Total other comprehensive income (loss)		3	4	8	9
Cumulative-effect of changes in accounting principles				3
Ending balance		12,917		12,917
Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss)		10	(2)	16	1
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)	(250)	(302)	(280)
Other comprehensive income before reclassifications: gains (losses)		(27)	11	51	82
Amounts reclassified from AOCI: (gains) losses	[3]	30	(15)	71	(56)
Net current period other comprehensive income (loss)		3	(4)	122	26
Cumulative-effect of changes in accounting principles				(64)
Less other comprehensive income attributable to noncontrolling interest				1
Ending balance		(245)	(254)	(245)	(254)
Deferred Gains and Losses on Derivatives-Hedging Activities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(8)	(10)	(12)	(8)
Other comprehensive income before reclassifications: gains (losses)		3	(2)	10	(5)
Amounts reclassified from AOCI: (gains) losses	[3]				1
Total other comprehensive income (loss)		3	(2)	10	(4)
Cumulative-effect of changes in accounting principles				(3)
Ending balance		(5)	(12)	(5)	(12)
Deferred Gains and Losses on Derivatives-Hedging Activities | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(24)	(23)	(23)	(24)
Other comprehensive income before reclassifications: gains (losses)		3	1	(4)	3
Amounts reclassified from AOCI: (gains) losses	[3]	5	(4)	16	(5)
Total other comprehensive income (loss)		8	(3)	12	(2)
Cumulative-effect of changes in accounting principles				(5)
Ending balance		(16)	(26)	(16)	(26)
Unrealized Gains and Losses on Investment Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(2)	630	747	569
Other comprehensive income before reclassifications: gains (losses)		(6)	48	(24)	141
Amounts reclassified from AOCI: (gains) losses	[3]	3	(4)	4	(36)
Net current period other comprehensive income (loss)		(3)	44	(20)	105
Cumulative-effect of changes in accounting principles				(732)
Ending balance		(5)	674	(5)	674
Unrealized Gains and Losses on Investment Securities | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(1)	61	74	54
Other comprehensive income before reclassifications: gains (losses)			6	(2)	17
Amounts reclassified from AOCI: (gains) losses	[3]				(4)
Total other comprehensive income (loss)			6	(2)	13
Cumulative-effect of changes in accounting principles				(73)
Ending balance		(1)	67	(1)	67
Unrecognized Pension and Other Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(1,286)	(1,058)	(1,101)	(1,082)
Amounts reclassified from AOCI: (gains) losses	[3]	18	14	60	38
Net current period other comprehensive income (loss)		18	14	60	38
Cumulative-effect of changes in accounting principles				(227)
Ending balance		(1,268)	(1,044)	(1,268)	(1,044)
Unrecognized Pension and Other Postretirement Benefit Costs | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(94)	(97)	(75)	(99)
Other comprehensive income before reclassifications: gains (losses)		0	0	0	0
Amounts reclassified from AOCI: (gains) losses	[3]	2	1	4	3
Total other comprehensive income (loss)		2	1	4	3
Cumulative-effect of changes in accounting principles				(21)
Ending balance		(92)	(96)	(92)	(96)
Other Comprehensive Loss From Equity Method Investee
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(2)	(4)	(3)	(6)
Other comprehensive income before reclassifications: gains (losses)				1	2
Net current period other comprehensive income (loss)				1	2
Ending balance		(2)	(4)	(2)	(4)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(1,538)	(682)	(659)	(799)
Other comprehensive income before reclassifications: gains (losses)		(33)	59	28	225
Amounts reclassified from AOCI: (gains) losses	[3]	51	(5)	135	(54)
Total other comprehensive income (loss)				162	171
Net current period other comprehensive income (loss)		18	54	163	171
Cumulative-effect of changes in accounting principles				(1,023)
Less other comprehensive income attributable to noncontrolling interest				1
Ending balance		(1,520)	(628)	(1,520)	(628)
Accumulated Other Comprehensive Income (Loss) | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(9)	51	62	46
Other comprehensive income before reclassifications: gains (losses)		3	4	8	12
Amounts reclassified from AOCI: (gains) losses	[3]				(3)
Total other comprehensive income (loss)		3	4	8	9
Cumulative-effect of changes in accounting principles				(76)
Ending balance		(6)	55	(6)	55
Accumulated Other Comprehensive Income (Loss) | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(118)	(120)	(98)	(123)
Other comprehensive income before reclassifications: gains (losses)		3	1	(4)	3
Amounts reclassified from AOCI: (gains) losses	[3]	7	(3)	20	(2)
Total other comprehensive income (loss)		10	(2)	16	1
Cumulative-effect of changes in accounting principles				(26)
Ending balance		$ (108)	$ (122)	$ (108)	$ (122)

[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.