Quarterly Financial Information (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Selected Quarterly Financial Information [Abstract]
Revenues	$ 354.8	$ 146.7	$ 222.9	$ 470.0	$ 362.7	$ 145.2	$ 201.1	$ 414.6	$ 1,194.4	$ 1,123.6	$ 1,109.9
Operating Income	106.6	63.8	73.7	122.8	107.8	54.4	56.3	124.8	366.9	343.3	328.2
Income from continuing operations	61.6	36.1	40.3	69.9	63.7	27.7	28.7	72.2	207.9	192.3	180.5
Discontinued operations, net of income taxes					0	0	68.8	78.1	0	146.9	212.8
Net income attributable to Questar	$ 61.6	$ 36.1	$ 40.3	$ 69.9	$ 63.7	$ 27.7	$ 97.5	$ 150.3	$ 207.9	$ 339.2	$ 393.3
Per share information attributable to Questar
Basic EPS from continuing operations	$ 0.34	$ 0.21	$ 0.22	$ 0.40	$ 0.36	$ 0.15	$ 0.17	$ 0.41	$ 1.17	$ 1.09	$ 1.03
Basic EPS attributable to Questar	$ 0.34	$ 0.21	$ 0.22	$ 0.40	$ 0.36	$ 0.15	$ 0.56	$ 0.86	$ 1.17	$ 1.93	$ 2.26
Diluted EPS from continuing operations	$ 0.34	$ 0.20	$ 0.22	$ 0.39	$ 0.36	$ 0.15	$ 0.16	$ 0.41	$ 1.16	$ 1.08	$ 1.02
Diluted EPS attributable to Questar	$ 0.34	$ 0.20	$ 0.22	$ 0.39	$ 0.36	$ 0.15	$ 0.55	$ 0.85	$ 1.16	$ 1.91	$ 2.23

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

The amount of net income or loss for the period per each share of common stock outstanding during the reporting period.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 21

-Article 9

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 128

-Paragraph 36, 37, 38

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 20

-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 18

-Article 7

+ Details

Name:	us-gaap_EarningsPerShareBasic
Namespace Prefix:	us-gaap_
Data Type:	us-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of net income or loss for the period per each share of common stock and dilutive common stock equivalents outstanding during the reporting period.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 128

-Paragraph 11, 12, 36

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 20

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 18

-Article 7

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 21

-Article 9

+ Details

Name:	us-gaap_EarningsPerShareDiluted
Namespace Prefix:	us-gaap_
Data Type:	us-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the income or loss from continuing operations attributable to the reporting entity which may also be defined as revenue less expenses and taxes from ongoing operations before extraordinary items and cumulative effects of changes in accounting principles, but after deduction of those portions of income or loss from continuing operations that are allocable to noncontrolling interests, if any.

+ References

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

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph 29

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

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph 28

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph 38

-Subparagraph b(1)

+ Details

Name:	us-gaap_IncomeLossFromContinuingOperations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of income (loss) from continuing operations per each share of common stock outstanding during the reporting period.

+ References

+ Details

Name:	us-gaap_IncomeLossFromContinuingOperationsPerBasicShare
Namespace Prefix:	us-gaap_
Data Type:	us-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of income (loss) from continuing operations available to each share of common stock outstanding during the reporting period and each share that would have been outstanding assuming the issuance of common shares for all dilutive potential common shares outstanding during the reporting period.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 21

-Article 9

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 128

-Paragraph 11, 12, 36, 37, 38

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 128

-Paragraph 40

-Subparagraph a

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 20

-Article 5

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 18

-Article 7

+ Details

Name:	us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare
Namespace Prefix:	us-gaap_
Data Type:	us-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the overall income (loss) from a disposal group apportioned to the parent that is classified as a component of the entity, net of income tax, reported as a separate component of income before extraordinary items and the cumulative effect of accounting changes after deduction or consideration of the amount which may be allocable to noncontrolling interests, if any. Includes the following (net of tax): income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

+ References

+ Details

Name:	us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The portion of consolidated profit or loss for the period, net of income taxes, which is attributable to the parent. If the entity does not present consolidated financial statements, the amount of profit or loss for the period, net of income taxes.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 19

-Article 5

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

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph 38

-Subparagraph d

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph A7

-Appendix A

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph 38

-Subparagraph a

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 20

-Article 9

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 130

-Paragraph 10, 15

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 87-21

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 28, 29, 30

+ Details

Name:	us-gaap_NetIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

Name:	us-gaap_OperatingIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Aggregate revenue recognized during the period (derived from goods sold, services rendered, insurance premiums, or other activities that constitute an entity's earning process). For financial services companies, also includes investment and interest income, and sales and trading gains.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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