Supplemental Gas and Oil Information - Unaudited Capitalized Cost (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Capitalized Costs Relating to Gas and Oil Producing Activities, by Segment [Line Items]
Total Wexpro capitalized costs	$ 1,688.4	$ 1,626.4
Accumulated depreciation, depletion and amortization	(757.3)	(689.8)
Net capitalized costs	937.5	943.8
Wexpro [Member]
Capitalized Costs Relating to Gas and Oil Producing Activities, by Segment [Line Items]
Proved properties	1,675.6	1,625.5
Unproved properties	12.8	0.9
Total Wexpro capitalized costs	1,688.4	1,626.4
Accumulated depreciation, depletion and amortization	(757.3)	(689.8)
Net capitalized costs	931.1	936.6
Questar Gas [Member]
Capitalized Costs Relating to Gas and Oil Producing Activities, by Segment [Line Items]
Net capitalized costs	$ 6.4	$ 7.2