Related-Party Transactions (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Virginia Electric and Power Company
Related Party Transaction [Line Items]
Commodity purchases from affiliates		$ 139	$ 137	$ 537	$ 349
Services provided by affiliates	[1]	112	112	232	224
Virginia Electric and Power Company | Affiliated Entity
Related Party Transaction [Line Items]
Services provided to related parties		5	7	11	12
Dominion Energy Gas Holdings, LLC
Related Party Transaction [Line Items]
Commodity purchases from affiliates			1	1
Services provided by affiliates	[2]	33	36	66	73
Services provided to related parties	[3]	61	36	113	75
Commodity purchases from affiliates		(2)
Other receivables	[4]	19		19		$ 12
Customer receivables from related parties						1
Affiliated notes receivable	[5]	18		18		20
Dominion Energy Gas Holdings, LLC | Affiliated Entity
Related Party Transaction [Line Items]
Services provided to related parties		16	$ 18	34	$ 36
Imbalances receivable from affiliates						$ 1
Imbalances payable to affiliates	[6]	$ 5		$ 5

[1] Includes capitalized expenditures of $38 million and $37 million for the three months ended June 30, 2018 and 2017, respectively, and $75 million and $71 million for the six months ended June 30, 2018 and 2017, respectively.

[2] Includes capitalized expenditures of $7 million and $12 million for the three months ended June 30, 2018 and 2017, respectively, and $17 million and $20 million for the six months ended June 30, 2018 and 2017, respectively.

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

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

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

[6] Amounts are presented in other current liabilities in Dominion Energy Gas’ Consolidated Balance Sheets.