Related-Party Transactions (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Related Party Transaction [Line Items]
Capital expenditures		$ 1,103	$ 1,435
Virginia Electric and Power Company
Related Party Transaction [Line Items]
Commodity purchases from affiliates		398	212
Services provided by affiliates	[1]	120	112
Capital expenditures		570	647
Virginia Electric and Power Company | Affiliated Entity
Related Party Transaction [Line Items]
Sales of natural gas and transportation and storage services to affiliates and Services provided to related parties		6	5
Virginia Electric and Power Company | Affiliated Entity | Services provided by affiliates
Related Party Transaction [Line Items]
Capital expenditures		37	34
Dominion Energy Gas Holdings, LLC
Related Party Transaction [Line Items]
Commodity purchases from affiliates		3
Sales of natural gas and transportation and storage services to affiliates and Services provided to related parties	[2]	52	39
Capital expenditures		138	134
Other receivables	[3]	17		$ 12
Customer receivables from related parties				1
Affiliated notes receivable	[4]	19		20
Dominion Energy Gas Holdings, LLC | Services provided by affiliates
Related Party Transaction [Line Items]
Services provided by affiliates	[5]	33	35
Dominion Energy Gas Holdings, LLC | Affiliated Entity
Related Party Transaction [Line Items]
Sales of natural gas and transportation and storage services to affiliates and Services provided to related parties		18	18
Imbalances receivable from affiliates				$ 1
Dominion Energy Gas Holdings, LLC | Affiliated Entity | Services provided by affiliates
Related Party Transaction [Line Items]
Capital expenditures		$ 10	$ 8

[1] Includes capitalized expenditures of $37 million and $34 million for the three months ended March 31, 2018 and 2017, respectively.

[2] Amounts primarily attributable to Atlantic Coast Pipeline, a related-party VIE.

[3] Represents amounts due from Atlantic Coast Pipeline, a related-party VIE.

[4] Amounts are presented in other deferred charges and other assets in Dominion Energy Gas' Consolidated Balance Sheets.

[5] Includes capitalized expenditures of $10 million and $8 million for the three months ended March 31, 2018 and 2017, respectively.