Variable Interest Entities (Narrative) (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) MW generator	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)		Sep. 30, 2017 generator
Variable Interest Entity [Line Items]
Securities due within one year	$ 3,603		$ 3,078	[1]
Long term debt	31,120		30,948	[1]
Virginia Electric and Power Company
Variable Interest Entity [Line Items]
Securities due within one year	600		850	[2]
Long term debt	11,090		10,496	[2]
Affiliated current borrowings	11		33	[2]
Dominion Energy Gas Holdings, LLC
Variable Interest Entity [Line Items]
Long term debt	3,579		3,570	[3]
Affiliated current borrowings	41		18	[3]
Variable Interest Entity, Primary Beneficiary | SBL Holdco
Variable Interest Entity [Line Items]
Securities due within one year	30
Long term debt	$ 332
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
Long term capacity contract non utility generators expired | generator					2
Aggregate generation capacity from long-term power and capacity contracts (MW) | MW	218
Remaining purchase commitments	$ 188
Payment for electric capacity	13	$ 28
Payment for electric energy	5	8
Variable Interest Entity, Not Primary Beneficiary | Virginia Electric and Power Company | DES
Variable Interest Entity [Line Items]
Shared services purchased	89	85
Variable Interest Entity, Not Primary Beneficiary | Virginia Electric and Power Company | DES | Payables to Affiliates
Variable Interest Entity [Line Items]
Affiliated current borrowings	43		36
Variable Interest Entity, Not Primary Beneficiary | Dominion Energy Gas Holdings, LLC | DES
Variable Interest Entity [Line Items]
Shared services purchased	32	$ 31
Variable Interest Entity, Not Primary Beneficiary | Dominion Energy Gas Holdings, LLC | DES | Payables to Affiliates
Variable Interest Entity [Line Items]
Affiliated current borrowings	$ 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.