Related-Party Transaction (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Related Party Transaction [Line Items]
Operating Leases, Future Minimum Payments Due, Current	$ 3.4
Questar Pipeline [Member] | Questar Gas [Member] | Revenues [Member]
Related Party Transaction [Line Items]
Related Party Transaction Revenue From Transactions With Related Party	74.1	73.9	72.1
Questar Pipeline [Member] | Questar Gas [Member] | General and Administrative Expense [Member]
Related Party Transaction [Line Items]
Related Party Transaction Expense From Transactions With Related Party	9.6	20.2	20.4
Questar Pipeline [Member] | Questar Corp [Member] | General and Administrative Expense [Member]
Related Party Transaction [Line Items]
Related Party Transaction Expense From Transactions With Related Party	22.2	7.0	4.1
Questar Pipeline [Member] | Questar Corp [Member] | Interest Expense [Member]
Related Party Transaction [Line Items]
Related Party Transaction Expense From Transactions With Related Party	0.1
Questar Pipeline [Member] | Questar Corp [Member] | Interest Income [Member]
Related Party Transaction [Line Items]
Related Party Transaction Revenue From Transactions With Related Party	0.1	0.3	0.5
Questar Pipeline [Member] | Affiliated Entity [Member] | Operating Lease Expense [Member]
Related Party Transaction [Line Items]
Related Party Transaction Expense From Transactions With Related Party	0.9	0.8	0.8
Operating Leases, Future Minimum Payments Due, Current	0.3
Questar Gas [Member] | Questar Corp [Member] | General and Administrative Expense [Member]
Related Party Transaction [Line Items]
Related Party Transaction Expense From Transactions With Related Party	46.9	13.2	8.4
Questar Gas [Member] | Questar Corp [Member] | Interest Expense [Member]
Related Party Transaction [Line Items]
Related Party Transaction Expense From Transactions With Related Party	0.3	0.4	0.3
Questar Gas [Member] | Questar Corp [Member] | Interest Income [Member]
Related Party Transaction [Line Items]
Related Party Transaction Revenue From Transactions With Related Party			0.1
Questar Gas [Member] | Affiliated Entity [Member] | Operating Lease Expense [Member]
Related Party Transaction [Line Items]
Related Party Transaction Expense From Transactions With Related Party	1.1	2.5	2.5
Operating Leases, Future Minimum Payments Due, Current	0.4
Questar Gas [Member] | Questar And Other Affiliates [Member] | General and Administrative Expense [Member]
Related Party Transaction [Line Items]
Related Party Transaction Expense From Transactions With Related Party	14.0	25.9	25.6
Questar Gas [Member] | Questar Pipeline [Member]
Related Party Transaction [Line Items]
Amount Of Mdth Per Day Reserved Transportation Capacity On Questar Pipeline	881
Questar Gas [Member] | Questar Pipeline [Member] | Transportation Storage And Processing Expense [Member]
Related Party Transaction [Line Items]
Related Party Transaction Expense From Transactions With Related Party	73.7	73.5	71.8
Questar Gas [Member] | Wexpro [Member] | Revenues [Member]
Related Party Transaction [Line Items]
Related Party Transaction Revenue From Transactions With Related Party	3.3	1.1	1.0
Questar Gas [Member] | Wexpro [Member] | Cost of Sales [Member]
Related Party Transaction [Line Items]
Related Party Transaction Expense From Transactions With Related Party	$ 253.4	$ 240.0	$ 225.0