Significant Financing Transactions (Details)	6 Months Ended
	Jun. 30, 2017 USD ($) Facility
Line of Credit Facility [Line Items]
Facility Limit	$ 1,000,000,000	[1]
Outstanding Commercial Paper	135,000,000	[1]
Outstanding Letters of Credit	0
Credit Facility $5 Billion
Line of Credit Facility [Line Items]
Facility Limit	500,000,000	[1]
Outstanding Commercial Paper	135,000,000	[1]
Outstanding Letters of Credit	0	[1]
Credit Facility $500 Million
Line of Credit Facility [Line Items]
Facility Limit	500,000,000	[1]
Outstanding Commercial Paper	0	[1]
Outstanding Letters of Credit	$ 0	[1]
Joint Revolving Credit Facility $5 Billion and Joint Revolving Credit Facility $500 Million
Line of Credit Facility [Line Items]
Number of joint revolving credit facility | Facility	2
Facility Limit	$ 1,000,000,000
Joint Revolving Credit Facility $5 Billion and Joint Revolving Credit Facility $500 Million | Line of Credit
Line of Credit Facility [Line Items]
Amount of sub-limit	250,000,000
Joint Revolving Credit Facility $5 Billion and Joint Revolving Credit Facility $500 Million | Letter of Credit
Line of Credit Facility [Line Items]
Facility Limit	$ 1,000,000,000

[1] A maximum of a combined $1.0 billion of the facilities is available to Questar Gas, assuming adequate capacity is available after giving effect to uses by co-borrowers Dominion Energy, Virginia Power and Dominion Energy Gas. Sub-limits for Questar Gas are set within the facility limit but can be changed at the option of the borrowers multiple times per year. At June 30, 2017, the sub-limit for Questar Gas was an aggregate $250 million. If Questar Gas has liquidity needs in excess of its sub-limit, the sub-limit may be changed or such needs may be satisfied through short-term intercompany borrowings from Dominion Energy. The maturity date for these facilities is April 2020. These credit facilities can be used to support bank borrowings and the issuance of commercial paper, as well as to support up to $1.0 billion (or the sub-limit, whichever is less) of letters of credit.