Related-Party Transactions (Dominion Energy Gas) (Narrative) (Details) - Dominion Energy Gas Holdings, LLC - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Short term demand note	$ 34	$ 118	[1]
Revolving Credit Facility | IRCA
Related Party Transaction [Line Items]
Short term demand note	34	118
Pension Benefits | Amounts Associated with the Dominion Pension Plan
Related Party Transaction [Line Items]
Amounts due from Dominion, noncurrent	725	697
Dominion Retiree Health and Welfare plan | Amounts Associated with the Dominion Retiree Health and Welfare Plan
Related Party Transaction [Line Items]
Amounts due from Dominion, noncurrent	$ 6	$ 2

[1] Dominion Energy Gas’ Consolidated Balance Sheet at December 31, 2016 has been derived from the audited Consolidated Balance Sheet at that date.