Related-Party Transaction (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Questar Gas [Member] | Questar Pipeline [Member]
Related Party Transaction [Line Items]
Amount of Mdth per day reserved transportation capacity on Questar Pipeline - peak months	916
Amount of Mdth per day reserved transportation capacity on Questar Pipeline - off-peak months	841
Revenues [Member] | Questar Gas [Member] | Wexpro [Member]
Related Party Transaction [Line Items]
Related Party Revenue	$ 2.5	$ 3.3	$ 1.1
Revenues [Member] | Questar Pipeline [Member] | Questar Gas [Member]
Related Party Transaction [Line Items]
Related Party Revenue	74.0	74.1	73.9
General and Administrative Expense [Member] | Questar Gas [Member] | Questar Corp [Member]
Related Party Transaction [Line Items]
Related Party Expense	42.1	46.9	13.2
General and Administrative Expense [Member] | Questar Gas [Member] | Questar And Other Affiliates [Member]
Related Party Transaction [Line Items]
Related Party Expense	13.6	14.0	25.9
General and Administrative Expense [Member] | Questar Pipeline [Member] | Questar Gas [Member]
Related Party Transaction [Line Items]
Related Party Expense	8.8	9.6	20.2
General and Administrative Expense [Member] | Questar Pipeline [Member] | Questar Corp [Member]
Related Party Transaction [Line Items]
Related Party Expense	22.0	22.2	7.0
Operating Lease Expense [Member] | Questar Gas [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Related Party Expense	0.4	1.1	2.5
Operating Lease Expense [Member] | Questar Pipeline [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Related Party Expense	0.3	0.9	0.8
Interest Expense [Member] | Questar Gas [Member] | Questar Corp [Member]
Related Party Transaction [Line Items]
Related Party Expense	0.6	0.3	0.4
Interest Expense [Member] | Questar Pipeline [Member] | Questar Corp [Member]
Related Party Transaction [Line Items]
Related Party Expense		0.1
Interest Income [Member] | Questar Pipeline [Member] | Questar Corp [Member]
Related Party Transaction [Line Items]
Related Party Revenue	0.1	2.5	0.3
Transportation Storage And Processing Expense [Member] | Questar Gas [Member] | Questar Pipeline [Member]
Related Party Transaction [Line Items]
Related Party Expense	73.6	73.7	73.5
Cost of Sales [Member] | Questar Gas [Member] | Wexpro [Member]
Related Party Transaction [Line Items]
Related Party Expense	$ 274.0	$ 253.4	$ 240.0