Related-Party Transaction (Details) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($) mdth	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Related Party Transaction [Line Items]
Oil and NGL income sharing (in millions)	$ 0.0	$ 0.0	$ 0.6
Questar Gas [Member] \| Sales [Member] \| Questar Pipeline [Member]
Related Party Transaction [Line Items]
Related Party Revenue	74.7	73.3	76.3
Questar Gas [Member] \| General and Administrative Expense [Member] \| Questar Pipeline [Member]
Related Party Transaction [Line Items]
Related Party Expense	3.6	3.8	3.5
Questar Corp [Member] \| General and Administrative Expense [Member] \| Questar Gas [Member]
Related Party Transaction [Line Items]
Related Party Expense	52.9	47.8	48.4
Questar Corp [Member] \| General and Administrative Expense [Member] \| Questar Pipeline [Member]
Related Party Transaction [Line Items]
Related Party Expense	27.1	25.8	28.2
Questar Corp [Member] \| Interest Expense [Member] \| Questar Gas [Member]
Related Party Transaction [Line Items]
Related Party Expense	0.4	0.1	0.5
Questar Corp [Member] \| Interest Income [Member] \| Questar Pipeline [Member]
Related Party Transaction [Line Items]
Related Party Revenue	0.1	0.1	0.2
Questar And Other Affiliates [Member] \| General and Administrative Expense [Member] \| Questar Gas [Member]
Related Party Transaction [Line Items]
Related Party Expense	6.7	6.1	6.7
Questar And Other Affiliates [Member] \| General and Administrative Expense [Member] \| Questar Pipeline [Member]
Related Party Transaction [Line Items]
Related Party Expense	$ 4.0	5.0	4.9
Questar Pipeline [Member] \| Questar Gas [Member]
Related Party Transaction [Line Items]
Amount of Mdth per day reserved transportation capacity on Questar Pipeline - peak months \| mdth	916
Amount of Mdth per day reserved transportation capacity on Questar Pipeline - off-peak months \| mdth	841
Questar Pipeline [Member] \| General and Administrative Expense [Member] \| Questar Gas [Member]
Related Party Transaction [Line Items]
Related Party Expense	$ 2.8	3.7	3.7
Questar Pipeline [Member] \| Cost of Sales [Member] \| Questar Gas [Member]
Related Party Transaction [Line Items]
Related Party Expense	73.0	72.9	73.0
Wexpro [Member] \| Sales [Member] \| Questar Gas [Member]
Related Party Transaction [Line Items]
Oil and NGL income sharing (in millions)	0.0	0.0	0.6
Wexpro [Member] \| Cost of Sales [Member] \| Questar Gas [Member]
Related Party Transaction [Line Items]
Related Party Expense	$ 319.0	$ 349.7	$ 294.6

Amount Of Mdth Per Day Reserved Transportation Capacity - Off-Peak Months

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Amount Of Mdth Per Day Reserved Transportation Capacity - Peak Months

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The amount of operating income received by subsidiary from operations as outlined by the agreement.

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Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Related Parties
-URI http://asc.fasb.org/extlink&oid=16382449

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07.1(c))
-URI http://asc.fasb.org/extlink&oid=6488393&loc=d3e606610-122999

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