Variable Interest Entities (Narrative) (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($) generator	Sep. 30, 2018 USD ($) MW	Sep. 30, 2017 USD ($) generator	Dec. 31, 2017 USD ($)
Variable Interest Entity [Line Items]
Securities due within one year	$ 3,101		$ 3,101		$ 3,078	[1]
Long term debt	32,188		32,188		30,948	[1]
Virginia Electric and Power Company
Variable Interest Entity [Line Items]
Securities due within one year	350		350		850	[2]
Long term debt	10,742		10,742		10,496	[2]
Affiliated current borrowings	15		15		33	[2]
Dominion Energy Gas Holdings, LLC
Variable Interest Entity [Line Items]
Long term debt	4,061		4,061		3,570	[3]
Affiliated current borrowings	24		24		18	[3]
Variable Interest Entity, Primary Beneficiary | SBL Holdco
Variable Interest Entity [Line Items]
Securities due within one year	27		27
Long term debt	326		$ 326
Variable Interest Entity (VIE) or Potential VIE, Information Unavailability | Virginia Electric and Power Company
Variable Interest Entity [Line Items]
Long term capacity contract non utility generators (generators) | generator				3
Number of expired non-utility generators | generator		2		2
Aggregate generation capacity from long-term power and capacity contracts (MW) | MW			218
Remaining purchase commitments	163		$ 163
Payment for electric capacity	13	$ 17	38	$ 73
Other energy-related purchases	4	5	14	20
Variable Interest Entity, Not Primary Beneficiary | Virginia Electric and Power Company | DES
Variable Interest Entity [Line Items]
Shared services purchased	79	83	251	251
Variable Interest Entity, Not Primary Beneficiary | Virginia Electric and Power Company | DES | Payables to Affiliates
Variable Interest Entity [Line Items]
Affiliated current borrowings	23		23		36
Variable Interest Entity, Not Primary Beneficiary | Dominion Energy Gas Holdings, LLC | DES
Variable Interest Entity [Line Items]
Shared services purchased	31	$ 31	94	$ 93
Variable Interest Entity, Not Primary Beneficiary | Dominion Energy Gas Holdings, LLC | DES | Payables to Affiliates
Variable Interest Entity [Line Items]
Affiliated current borrowings	$ 11		$ 11		$ 14

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