Related Party Transactions (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) MMBTU	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Related Party Transaction [Line Items]
Current receivable from affiliates	$ 72,600,000		$ 72,600,000		$ 0	[1]
Affiliated Entity | Technical Services Provided to Affiliates
Related Party Transaction [Line Items]
Revenue from affiliated companies	1,300,000	$ 1,100,000	4,500,000	$ 4,800,000
Affiliated Entity | Charges for Certain Administrative Functions
Related Party Transaction [Line Items]
Operating expenses from affiliated companies	22,700,000	13,800,000	$ 41,000,000	42,900,000
Affiliated Entity | Questar Pipeline | Reserved Transportation Capacity | Reserved Transportation Capacity on Pipeline System during Heating Season
Related Party Transaction [Line Items]
Reserved transportation capacity (Mdth per day) | MMBTU			956,000
Affiliated Entity | Questar Pipeline | Reserved Transportation Capacity | Reserved Transportation Capacity on Pipeline System during Off-Peak Months
Related Party Transaction [Line Items]
Reserved transportation capacity (Mdth per day) | MMBTU			841,000
Affiliated Entity | Questar Pipeline | Transportation, Storage and Processing Services provided by Related Parties
Related Party Transaction [Line Items]
Cost of natural gas sold from affiliated companies	17,300,000	17,500,000	$ 53,900,000	54,300,000
Affiliated Entity | Wexpro | Payments to Related Party for Operation of Cost of Service Gas Properties
Related Party Transaction [Line Items]
Cost of natural gas sold from affiliated companies	77,700,000	80,700,000	236,400,000	241,000,000
Dominion Questar Corporation | Dominion Questar Corporation | Merger and Restructuring Costs from Dominion Questar Combination
Related Party Transaction [Line Items]
Merger and restructuring costs	9,700,000	$ 0	9,700,000	$ 0
Dominion Questar Corporation | Dominion Questar Corporation | Participation in Dominion Questar Benefit Plans
Related Party Transaction [Line Items]
Current receivable from affiliates	$ 72,600,000		$ 72,600,000
Noncurrent receivable from affiliates					$ 67,500,000

[1] Derived from 2015 audited financial statements