Variable Interest Entities (Narrative) (Detail) $ in Millions		3 Months Ended		6 Months Ended		9 Months Ended
		Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) MW	Jun. 30, 2017 USD ($)	Sep. 30, 2017 generator	Dec. 31, 2017 USD ($)
Variable Interest Entity [Line Items]
Securities due within one year		$ 2,950		$ 2,950			$ 3,078	[1]
Long term debt		32,115		32,115			30,948	[1]
Virginia Electric and Power Company
Variable Interest Entity [Line Items]
Securities due within one year	[2]						850
Long term debt		11,091		11,091			10,496	[2]
Affiliated current borrowings		25		25			33	[2]
Dominion Energy Gas Holdings, LLC
Variable Interest Entity [Line Items]
Long term debt		4,062		4,062			3,570	[3]
Affiliated current borrowings		56		56			18	[3]
Variable Interest Entity, Primary Beneficiary | SBL Holdco
Variable Interest Entity [Line Items]
Securities due within one year		29		29
Long term debt		324		$ 324
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
Aggregate generation capacity from long-term power and capacity contracts (MW) | MW				218
Remaining purchase commitments		175		$ 175
Payment for electric capacity		12	$ 28	25	$ 56
Other energy-related purchases		5	7	10	15
Variable Interest Entity, Not Primary Beneficiary | Virginia Electric and Power Company | DES
Variable Interest Entity [Line Items]
Shared services purchased		83	83	172	168
Variable Interest Entity, Not Primary Beneficiary | Virginia Electric and Power Company | DES | Payables to Affiliates
Variable Interest Entity [Line Items]
Affiliated current borrowings		35		35			36
Variable Interest Entity, Not Primary Beneficiary | Dominion Energy Gas Holdings, LLC | DES
Variable Interest Entity [Line Items]
Shared services purchased		31	$ 31	63	$ 62
Variable Interest Entity, Not Primary Beneficiary | Dominion Energy Gas Holdings, LLC | DES | Payables to Affiliates
Variable Interest Entity [Line Items]
Affiliated current borrowings		$ 12		$ 12			$ 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.