Significant Financing Transactions (Details)		3 Months Ended
		Mar. 31, 2018 USD ($) Facility	Sep. 30, 2018 USD ($)	Apr. 30, 2018 USD ($)
Joint Revolving Credit Facilities
Line of Credit Facility [Line Items]
Joint revolving credit facility, amount		$ 6,000,000,000
Credit Facility $1.0 Billion
Line of Credit Facility [Line Items]
Facility Limit	[1]		$ 1,000,000,000
Outstanding Commercial Paper	[1]		110,000,000
Outstanding Letters of Credit	[1]		0
Joint Revolving Credit Facility $1.0 Billion
Line of Credit Facility [Line Items]
Number of joint revolving credit facility | Facility		2
Facility Limit			1,000,000,000
Joint Revolving Credit Facility $1.0 Billion | Line of Credit
Line of Credit Facility [Line Items]
Amount of sub-limit			250,000,000
Joint Revolving Credit Facility $1.0 Billion | Letter of Credit
Line of Credit Facility [Line Items]
Facility Limit			$ 1,000,000,000
Private Placement Senior Note Payable at 3.30% | Private Placement Senior Note Payable
Line of Credit Facility [Line Items]
Amount of note				$ 50,000,000
Interest rate percentage				3.30%
Private Placement Senior Note Payable at 3.97% | Private Placement Senior Note Payable
Line of Credit Facility [Line Items]
Amount of note				$ 100,000,000
Interest rate percentage				3.97%

[1] A maximum of $1.0 billion of the facility 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. The sub-limit for Questar Gas is set within the facility limit but can be changed at the option of the borrowers multiple times per year. At September 30, 2018, the sub-limit for Questar Gas was $250.0 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 this facility is March 2023. This credit facility 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.