Amount of natural gas bought under previous purchase agreements.

No definition available.

Name:	str_NaturalGasPurchasedUnderAgreements
Namespace Prefix:	str_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_LongTermPurchaseCommitmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum amount of purchase arrangement maturing in the fifth fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligationDueInFifthYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum amount of purchase arrangement maturing in the fourth fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligationDueInFourthYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum amount of purchase arrangement maturing in the next fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligationDueInNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum amount of purchase arrangement maturing in the second fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligationDueInSecondYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum amount of purchase arrangement maturing in the third fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligationDueInThirdYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Contingencies, Commitments and Leases Commitments (Details) (Questar Gas [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Long-term Purchase Commitment [Line Items]
Natural gas purchased under agreements	$ 135.8str_NaturalGasPurchasedUnderAgreements	$ 186.5str_NaturalGasPurchasedUnderAgreements	$ 104.1str_NaturalGasPurchasedUnderAgreements
Gas purchase agreements [Member]
Long-term Purchase Commitment [Line Items]
2015	18.3
2016	15.2
2017	18.2
2018	21.2
2019	21.2
Transportation and storage commitments - Related party [Member]
Long-term Purchase Commitment [Line Items]
2015	74.4
2016	73.4
2017	46.7
2018	13.4
2019	5.2
Transportation and gathering commitments - Third party [Member]
Long-term Purchase Commitment [Line Items]
2015	29.0
2016	29.0
2017	29.0
2018	26.3
2019	$ 24.9