Share-Based Compensation Restricted stock units (Details) (USD $)	12 Months Ended
Dec. 31, 2014
Restricted Stock Units [Member]
Transactions under the terms of the LTSIP - shares [Roll Forward]
Balance at December 31, 2013	316,268
Granted	351,066
Vested	(131,007)
Forfeited	(10,225)
Balance at December 31, 2014	526,102
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at December 31, 2013	$ 23.62
Granted	$ 23.59
Vested	$ 23.64
Forfeited	$ 23.60
Balance at December 31, 2014	$ 23.60
Share-based awards other than options, additional disclosures [Abstract]
Weighted-average remaining vesting period of share-based awards issued (in months)	12 months
Number of shares of common stock to be issued for each vested restricted stock unit (RSU)	1
Vesting period for share-based award (in years)	3 years
Deferred Restricted Stock Units (RSUs) [Member]
Transactions under the terms of the LTSIP - shares [Roll Forward]
Balance at December 31, 2014	21,860
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at December 31, 2014	$ 23.61
Share-based awards other than options, additional disclosures [Abstract]
Weighted-average remaining vesting period of share-based awards issued (in months)	2 months
Number of shares of common stock to be issued for each vested restricted stock unit (RSU)	1
Vesting period for share-based award (in years)	1 year
Minimum [Member] \| Restricted Stock Units [Member]
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at December 31, 2013	$ 22.17
Granted	$ 22.14
Vested	$ 22.17
Forfeited	$ 23.60
Balance at December 31, 2014	$ 22.14
Maximum [Member] \| Restricted Stock Units [Member]
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at December 31, 2013	$ 25.44
Granted	$ 24.70
Vested	$ 25.44
Forfeited	$ 23.62
Balance at December 31, 2014	$ 24.70
Questar Gas [Member] \| Restricted Stock Units [Member]
Transactions under the terms of the LTSIP - shares [Roll Forward]
Balance at December 31, 2014	82,351
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at December 31, 2014	$ 23.61
Share-based awards other than options, additional disclosures [Abstract]
Weighted-average remaining vesting period of share-based awards issued (in months)	12 months
Questar Gas [Member] \| Minimum [Member] \| Restricted Stock Units [Member]
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at December 31, 2014	$ 23.09
Questar Gas [Member] \| Maximum [Member] \| Restricted Stock Units [Member]
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at December 31, 2014	$ 23.62
Questar Pipeline [Member] \| Restricted Stock Units [Member]
Transactions under the terms of the LTSIP - shares [Roll Forward]
Balance at December 31, 2014	95,841
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at December 31, 2014	$ 23.59
Share-based awards other than options, additional disclosures [Abstract]
Weighted-average remaining vesting period of share-based awards issued (in months)	12 months
Questar Pipeline [Member] \| Minimum [Member] \| Restricted Stock Units [Member]
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at December 31, 2014	$ 23.09
Questar Pipeline [Member] \| Maximum [Member] \| Restricted Stock Units [Member]
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]
Balance at December 31, 2014	$ 23.62

Number of shares of common stock to be issued for each vested restricted stock unit (RSU)

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

-Section 50

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-Subparagraph (c)(1)(iv)(3)

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(3)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

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-Paragraph 2

-Subparagraph (c)(2)(iii)(1)

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(i)-(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(i)-(ii)

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- Definition

Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (e)(1)

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(2)

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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(2)

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