Acquisitions and Dispositions (Acquisition of Dominion Energy Questar) (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		1 Months Ended			3 Months Ended	9 Months Ended
	Sep. 16, 2016	Sep. 30, 2016	Aug. 31, 2016	Apr. 30, 2016	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Issuance of common stock						$ 1,232	$ 2,079
Borrowing under term loan							1,200
Issuance of common stock						$ 1,233	$ 2,079
Dominion Energy Questar Corporation
Business Acquisition [Line Items]
Price per share	$ 25.00
Total consideration	$ 4,400
Number of shares of Dominion Questar outstanding at closing	175.5
August 2016 issuance of senior notes			$ 1,300
Increase to goodwill related modifications to valuation amounts					$ 6
Dominion Energy Questar Corporation | Term loan agreement
Business Acquisition [Line Items]
Borrowing under term loan		$ 1,200
Dominion Energy Questar Corporation | Underwritten Public Offering
Business Acquisition [Line Items]
Issuance of common stock				$ 500
Dominion Energy Questar Corporation | Series A RSNs
Business Acquisition [Line Items]
Issuance of common stock			$ 1,400