Schedule of Valuation and Qualifying Accounts (Details) (Allowance for Bad Debt [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	$ 1.7	$ 3.1	$ 3.2
Amounts charged to expense	1.7	0.2	1.2
Deductions for accounts written off and other	(1.7)	(1.6)	(1.3)
Ending Balance	1.7	1.7	3.1
Questar Gas [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	1.4	2.8	2.9
Amounts charged to expense	1.7	0.2	1.1
Deductions for accounts written off and other	(1.7)	(1.6)	(1.2)
Ending Balance	1.4	1.4	2.8
Questar Pipeline [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	0.3	0.3	0.3
Amounts charged to expense	0	0	0.1
Deductions for accounts written off and other	0	0	(0.1)
Ending Balance	$ 0.3	$ 0.3	$ 0.3

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Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 09

-Article 12

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- Definition

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- Definition

Total of the deductions in a given period to allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs, representing receivables written off as uncollectible and portions of the reserves utilized, respectively.

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