Supplemental Gas and Oil Information - Unaudited Capitalized Cost (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Capitalized Costs Relating to Gas and Oil Producing Activities, by Segment [Line Items]
Total Wexpro capitalized costs	$ 1,654.4	$ 1,688.4
Accumulated depreciation, depletion and amortization	(789.9)	(757.3)
Net capitalized costs	870.3	937.5
Wexpro [Member]
Capitalized Costs Relating to Gas and Oil Producing Activities, by Segment [Line Items]
Proved properties	1,649.2	1,675.6
Unproved properties	5.2	12.8
Total Wexpro capitalized costs	1,654.4	1,688.4
Accumulated depreciation, depletion and amortization	(789.9)	(757.3)
Net capitalized costs	864.5	931.1
Questar Gas [Member]
Capitalized Costs Relating to Gas and Oil Producing Activities, by Segment [Line Items]
Net capitalized costs	$ 5.8	$ 6.4