Asset Retirement Obligations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs at beginning of year	$ 67.7	$ 67.2
Accretion	3.4	3.3
Liabilities incurred	3.3	6.0
Revisions in estimated cash flows	(2.7)	(6.9)
Liabilities settled	(2.4)	(1.9)
AROs at end of year	69.3	67.7
Asset Retirement Obligations By Line Of Business [Abstract]
AROs by line of business	69.3	67.7
Questar Gas [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs at end of year	0.6	0.6
Asset Retirement Obligations By Line Of Business [Abstract]
AROs by line of business	0.6	0.6
Wexpro [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs at end of year	66.3	64.9
Asset Retirement Obligations By Line Of Business [Abstract]
AROs by line of business	66.3	64.9
Questar Pipeline [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs at end of year	2.3	2.2
Asset Retirement Obligations By Line Of Business [Abstract]
AROs by line of business	2.3	2.2
Questar Corp [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs at end of year	0.1	0
Asset Retirement Obligations By Line Of Business [Abstract]
AROs by line of business	$ 0.1	$ 0

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Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848

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-Publisher FASB

-Name Accounting Standards Codification

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Amount of asset retirement obligations incurred during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

+ References

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

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Amount of the Increase or Decrease in the amount of the asset retirement obligation during the current period for changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

+ References

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

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-Section 50

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Noncurrent portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

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