Supplemental Gas and Oil Information Capitalized Costs of Cost-of-Service Activities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Capitalized Costs Relating To Oil And Gas Producing Activities By Segment [Line Items]
Capitalized Costs, Oil and Gas Producing Activities, Net	$ 788.2	$ 717.1
Wexpro [Member]
Capitalized Costs Relating To Oil And Gas Producing Activities By Segment [Line Items]
Capitalized Costs, Oil and Gas Producing Activities, Net	780.4	708.6
Questar Gas [Member]
Capitalized Costs Relating To Oil And Gas Producing Activities By Segment [Line Items]
Capitalized Costs, Oil and Gas Producing Activities, Net	$ 7.8	$ 8.5