Supplemental Gas and Oil Information - Unaudited Capitalized Costs of Cost-of-Service Activities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Capitalized Costs Relating to Cost-of-Service Gas and Oil Producing Activities, by Segment [Line Items]
Total capitalized costs of cost-of-service activities	$ 943.8	$ 788.2
Wexpro [Member]
Capitalized Costs Relating to Cost-of-Service Gas and Oil Producing Activities, by Segment [Line Items]
Total capitalized costs of cost-of-service activities	936.6	780.4
Questar Gas [Member]
Capitalized Costs Relating to Cost-of-Service Gas and Oil Producing Activities, by Segment [Line Items]
Total capitalized costs of cost-of-service activities	$ 7.2	$ 7.8