Supplemental Gas and Oil Information Capitalized Costs of Cost-of-Service Activities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Capitalized Costs Relating To Oil And Gas Producing Activities By Segment [Line Items]
Capitalized Costs, Oil and Gas Producing Activities, Net	$ 717.1	$ 630.7
Wexpro [Member]
Capitalized Costs Relating To Oil And Gas Producing Activities By Segment [Line Items]
Capitalized Costs, Oil and Gas Producing Activities, Net	708.6	621.3
Questar Gas [Member]
Capitalized Costs Relating To Oil And Gas Producing Activities By Segment [Line Items]
Capitalized Costs, Oil and Gas Producing Activities, Net	$ 8.5	$ 9.4