Related-Party Transactions (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Virginia Electric and Power Company
Related Party Transaction [Line Items]
Commodity purchases from affiliates		$ 196	$ 170	$ 733	$ 519
Services provided by affiliates	[1]	106	109	338	333
Virginia Electric and Power Company | Affiliated Entity
Related Party Transaction [Line Items]
Services provided to related parties		6	5	17	17
Dominion Energy Gas Holdings, LLC
Related Party Transaction [Line Items]
Commodity purchases from affiliates		1	2	2	4
Services provided by affiliates	[2]	32	36	98	106
Services provided to related parties	[3]	53	37	166	113
Other receivables	[4]	15		15		$ 12
Customer receivables from related parties		1		1		1
Affiliated notes receivable	[5]	17		17		20
Dominion Energy Gas Holdings, LLC | Affiliated Entity
Related Party Transaction [Line Items]
Services provided to related parties		17	$ 15	51	$ 51
Imbalances receivable from affiliates						$ 1
Imbalances payable to affiliates	[6]	$ 7		$ 7

[1] Includes capitalized expenditures of $34 million and $33 million for the three months ended September 30, 2018 and 2017, respectively, and $109 million and $104 million for the nine months ended September 30, 2018 and 2017, respectively.

[2] Includes capitalized expenditures of $10 million and $13 million for the three months ended September 30, 2018 and 2017, respectively, and $27 million and $33 million for the nine months ended September 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.