2.4.0.82406402 - Disclosure - Fair Value Measurements (Details)truefalseIn Millions, unless otherwise specifiedfalse1false USDfalsefalse$I2013Q2_us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxis_us-gaap_CarryingReportedAmountFairValueDisclosureMemberhttp://www.sec.gov/CIK0000751652instant2013-06-30T00:00:000001-01-01T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$2false USDfalsefalse$I2012Q4_us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxis_us-gaap_CarryingReportedAmountFairValueDisclosureMemberhttp://www.sec.gov/CIK0000751652instant2012-12-31T00:00:000001-01-01T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$3false USDfalsefalse$I2012Q2_us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxis_us-gaap_CarryingReportedAmountFairValueDisclosureMemberhttp://www.sec.gov/CIK0000751652instant2012-06-30T00:00:000001-01-01T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$1false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse1false USDtruefalse$I2013Q2_us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxis_us-gaap_CarryingReportedAmountFairValueDisclosureMemberhttp://www.sec.gov/CIK0000751652instant2013-06-30T00:00:000001-01-01T00:00:00falsefalseCarrying Amount [Member]us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_CarryingReportedAmountFairValueDisclosureMemberus-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisexplicitMemberusdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Carrying Amount [Member]2true 4us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial assets [Abstract]3false 5us-gaap_CashAndCashEquivalentsFairValueDisclosureus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse00USD$falsetruefalse2truefalsefalse1680000016.8USD$falsetruefalse3truefalsefalse00USD$falsetruefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8 -Footnote 2 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 8, 9, 10 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Cash and cash equivalents4false 5us-gaap_InvestmentsFairValueDisclosureus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse1650000016.5USD$falsefalsefalse2truefalsefalse1550000015.5USD$falsefalsefalse3truefalsefalse1470000014.7USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents investment securities as of the balance sheet date which may include marketable securities, derivative financial instruments, and investments accounted for under the equity method.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 13 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 12 -Subparagraph a -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph a, f, g -Article 7 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=16383099&loc=d3e24584-111560 false2Long-term investment5true 4us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial liabilities [Abstract]6false 5str_ChecksOutstandingInExcessOfCashBalancesFairValueDisclosurestr_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse5000000.5USD$falsefalsefalse2truefalsefalse00USD$falsefalsefalse3truefalsefalse1180000011.8USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. This item represents checks outstanding in excess of cash balances as of the balance sheet date.No definition available.false2Checks outstanding in excess of cash balances7false 5us-gaap_ShorttermDebtFairValueus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse206000000206.0USD$falsefalsefalse2truefalsefalse263000000263.0USD$falsefalsefalse3truefalsefalse190000000190.0USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.No definition available.false2Short-term debt8false 5us-gaap_LongTermDebtFairValueus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse11000000001100.0USD$falsefalsefalse2truefalsefalse11409000001140.9USD$falsefalsefalse3truefalsefalse10834000001083.4USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.No definition available.false2Long-term debt, including current portion9false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4false USDtruefalse$I2013Q2_us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxis_us-gaap_EstimateOfFairValueFairValueDisclosureMember_us-gaap_FairValueByFairValueHierarchyLevelAxis_us-gaap_FairValueInputsLevel1Memberhttp://www.sec.gov/CIK0000751652instant2013-06-30T00:00:000001-01-01T00:00:00falsefalseEstimated Fair Value [Member]us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_EstimateOfFairValueFairValueDisclosureMemberus-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisexplicitMemberfalsefalseFair Value, Inputs, Level 1 [Member]us-gaap_FairValueByFairValueHierarchyLevelAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_FairValueInputsLevel1Memberus-gaap_FairValueByFairValueHierarchyLevelAxisexplicitMemberusdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]10true 4us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial assets [Abstract]11false 5us-gaap_CashAndCashEquivalentsFairValueDisclosureus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse00USD$falsefalsefalse2truefalsefalse1680000016.8USD$falsefalsefalse3truefalsefalse00USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8 -Footnote 2 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 8, 9, 10 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Cash and cash equivalents12false 5us-gaap_InvestmentsFairValueDisclosureus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse1650000016.5USD$falsefalsefalse2truefalsefalse1550000015.5USD$falsefalsefalse3truefalsefalse1470000014.7USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents investment securities as of the balance sheet date which may include marketable securities, derivative financial instruments, and investments accounted for under the equity method.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 13 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 12 -Subparagraph a -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph a, f, g -Article 7 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=16383099&loc=d3e24584-111560 false2Long-term investment13true 4us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial liabilities [Abstract]14false 5str_ChecksOutstandingInExcessOfCashBalancesFairValueDisclosurestr_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse5000000.5USD$falsefalsefalse2truefalsefalse00USD$falsefalsefalse3truefalsefalse1180000011.8USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. This item represents checks outstanding in excess of cash balances as of the balance sheet date.No definition available.false2Checks outstanding in excess of cash balances15false 5us-gaap_ShorttermDebtFairValueus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse206000000206.0USD$falsefalsefalse2truefalsefalse263000000263.0USD$falsefalsefalse3truefalsefalse190000000190.0USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.No definition available.false2Short-term debt16false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse7false USDtruefalse$I2013Q2_us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxis_us-gaap_EstimateOfFairValueFairValueDisclosureMember_us-gaap_FairValueByFairValueHierarchyLevelAxis_us-gaap_FairValueInputsLevel2Memberhttp://www.sec.gov/CIK0000751652instant2013-06-30T00:00:000001-01-01T00:00:00falsefalseEstimated Fair Value [Member]us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_EstimateOfFairValueFairValueDisclosureMemberus-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisexplicitMemberfalsefalseFair Value, Inputs, Level 2 [Member]us-gaap_FairValueByFairValueHierarchyLevelAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_FairValueInputsLevel2Memberus-gaap_FairValueByFairValueHierarchyLevelAxisexplicitMemberusdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]17true 4us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial liabilities [Abstract]18false 5us-gaap_LongTermDebtFairValueus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse12003000001200.3USD$falsefalsefalse2truefalsefalse13031000001303.1USD$falsefalsefalse3truefalsefalse12455000001245.5USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.No definition available.false2Long-term debt, including current portion19false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse10false USDtruefalse$I2013Q2_dei_LegalEntityAxis_str_QuestarGasMember_us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxis_us-gaap_CarryingReportedAmountFairValueDisclosureMemberhttp://www.sec.gov/CIK0000751652instant2013-06-30T00:00:000001-01-01T00:00:00falsefalseQuestar Gas [Member]dei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldistr_QuestarGasMemberdei_LegalEntityAxisexplicitMemberfalsefalseCarrying Amount [Member]us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_CarryingReportedAmountFairValueDisclosureMemberus-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisexplicitMemberusdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Questar Gas [Member] | Carrying Amount [Member]20true 4us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial assets [Abstract]21false 5us-gaap_CashAndCashEquivalentsFairValueDisclosureus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse00USD$falsefalsefalse2truefalsefalse14000001.4USD$falsefalsefalse3truefalsefalse00USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8 -Footnote 2 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 8, 9, 10 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Cash and cash equivalents22true 4us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial liabilities [Abstract]23false 5str_ChecksOutstandingInExcessOfCashBalancesFairValueDisclosurestr_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse34000003.4USD$falsefalsefalse2truefalsefalse00USD$falsefalsefalse3truefalsefalse54000005.4USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. This item represents checks outstanding in excess of cash balances as of the balance sheet date.No definition available.false2Checks outstanding in excess of cash balances24false 5str_NotesPayableAffiliatedFairValueDisclosurestr_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse137300000137.3USD$falsefalsefalse2truefalsefalse166100000166.1USD$falsefalsefalse3truefalsefalse102100000102.1USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents affiliated notes payable as of the balance sheet date.No definition available.false2Notes payable to Questar25false 5us-gaap_LongTermDebtFairValueus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse386500000386.5USD$falsefalsefalse2truefalsefalse426500000426.5USD$falsefalsefalse3truefalsefalse368000000368.0USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.No definition available.false2Long-term debt, including current portion26false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse13false USDtruefalse$I2013Q2_dei_LegalEntityAxis_str_QuestarGasMember_us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxis_us-gaap_EstimateOfFairValueFairValueDisclosureMember_us-gaap_FairValueByFairValueHierarchyLevelAxis_us-gaap_FairValueInputsLevel1Memberhttp://www.sec.gov/CIK0000751652instant2013-06-30T00:00:000001-01-01T00:00:00falsefalseQuestar Gas [Member]dei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldistr_QuestarGasMemberdei_LegalEntityAxisexplicitMemberfalsefalseEstimated Fair Value [Member]us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_EstimateOfFairValueFairValueDisclosureMemberus-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisexplicitMemberfalsefalseFair Value, Inputs, Level 1 [Member]us-gaap_FairValueByFairValueHierarchyLevelAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_FairValueInputsLevel1Memberus-gaap_FairValueByFairValueHierarchyLevelAxisexplicitMemberusdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Questar Gas [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]27true 4us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial assets [Abstract]28false 5us-gaap_CashAndCashEquivalentsFairValueDisclosureus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse00USD$falsefalsefalse2truefalsefalse14000001.4USD$falsefalsefalse3truefalsefalse00USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8 -Footnote 2 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 8, 9, 10 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Cash and cash equivalents29true 4us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial liabilities [Abstract]30false 5str_ChecksOutstandingInExcessOfCashBalancesFairValueDisclosurestr_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse34000003.4USD$falsefalsefalse2truefalsefalse00USD$falsefalsefalse3truefalsefalse54000005.4USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. This item represents checks outstanding in excess of cash balances as of the balance sheet date.No definition available.false2Checks outstanding in excess of cash balances31false 5str_NotesPayableAffiliatedFairValueDisclosurestr_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse137300000137.3USD$falsefalsefalse2truefalsefalse166100000166.1USD$falsefalsefalse3truefalsefalse102100000102.1USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents affiliated notes payable as of the balance sheet date.No definition available.false2Notes payable to Questar32false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse16false USDtruefalse$I2013Q2_dei_LegalEntityAxis_str_QuestarGasMember_us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxis_us-gaap_EstimateOfFairValueFairValueDisclosureMember_us-gaap_FairValueByFairValueHierarchyLevelAxis_us-gaap_FairValueInputsLevel2Memberhttp://www.sec.gov/CIK0000751652instant2013-06-30T00:00:000001-01-01T00:00:00falsefalseQuestar Gas [Member]dei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldistr_QuestarGasMemberdei_LegalEntityAxisexplicitMemberfalsefalseEstimated Fair Value [Member]us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_EstimateOfFairValueFairValueDisclosureMemberus-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisexplicitMemberfalsefalseFair Value, Inputs, Level 2 [Member]us-gaap_FairValueByFairValueHierarchyLevelAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_FairValueInputsLevel2Memberus-gaap_FairValueByFairValueHierarchyLevelAxisexplicitMemberusdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Questar Gas [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]33true 4us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial liabilities [Abstract]34false 5us-gaap_LongTermDebtFairValueus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse433300000433.3USD$falsefalsefalse2truefalsefalse503700000503.7USD$falsefalsefalse3truefalsefalse449100000449.1USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.No definition available.false2Long-term debt, including current portion35false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse19false USDtruefalse$I2013Q2_dei_LegalEntityAxis_str_QuestarPipelineMember_us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxis_us-gaap_CarryingReportedAmountFairValueDisclosureMemberhttp://www.sec.gov/CIK0000751652instant2013-06-30T00:00:000001-01-01T00:00:00falsefalseQuestar Pipeline [Member]dei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldistr_QuestarPipelineMemberdei_LegalEntityAxisexplicitMemberfalsefalseCarrying Amount [Member]us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_CarryingReportedAmountFairValueDisclosureMemberus-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisexplicitMemberusdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Questar Pipeline [Member] | Carrying Amount [Member]36true 4us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial assets [Abstract]37false 5us-gaap_CashAndCashEquivalentsFairValueDisclosureus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse57000005.7USD$falsefalsefalse2truefalsefalse71000007.1USD$falsefalsefalse3truefalsefalse3000000.3USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8 -Footnote 2 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 8, 9, 10 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Cash and cash equivalents38false 5str_NotesReceivableAffiliatedFairValueDisclosurestr_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse3440000034.4USD$falsefalsefalse2truefalsefalse3870000038.7USD$falsefalsefalse3truefalsefalse1880000018.8USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. An amount representing an agreement for an unconditional promise by the maker to pay the affiliated Company (holder) a definite sum of money at a future date(s).No definition available.false2Notes receivable from Questar39true 4us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial liabilities [Abstract]40false 5us-gaap_LongTermDebtFairValueus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse458900000458.9USD$falsefalsefalse2truefalsefalse458900000458.9USD$falsefalsefalse3truefalsefalse459000000459.0USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.No definition available.false2Long-term debt, including current portion41false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse22false USDtruefalse$I2013Q2_dei_LegalEntityAxis_str_QuestarPipelineMember_us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxis_us-gaap_EstimateOfFairValueFairValueDisclosureMember_us-gaap_FairValueByFairValueHierarchyLevelAxis_us-gaap_FairValueInputsLevel1Memberhttp://www.sec.gov/CIK0000751652instant2013-06-30T00:00:000001-01-01T00:00:00falsefalseQuestar Pipeline [Member]dei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldistr_QuestarPipelineMemberdei_LegalEntityAxisexplicitMemberfalsefalseEstimated Fair Value [Member]us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_EstimateOfFairValueFairValueDisclosureMemberus-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisexplicitMemberfalsefalseFair Value, Inputs, Level 1 [Member]us-gaap_FairValueByFairValueHierarchyLevelAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_FairValueInputsLevel1Memberus-gaap_FairValueByFairValueHierarchyLevelAxisexplicitMemberusdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Questar Pipeline [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]42true 4us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial assets [Abstract]43false 5us-gaap_CashAndCashEquivalentsFairValueDisclosureus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse57000005.7USD$falsefalsefalse2truefalsefalse71000007.1USD$falsefalsefalse3truefalsefalse3000000.3USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8 -Footnote 2 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 8, 9, 10 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Cash and cash equivalents44false 5str_NotesReceivableAffiliatedFairValueDisclosurestr_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse3440000034.4USD$falsefalsefalse2truefalsefalse3870000038.7USD$falsefalsefalse3truefalsefalse1880000018.8USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. An amount representing an agreement for an unconditional promise by the maker to pay the affiliated Company (holder) a definite sum of money at a future date(s).No definition available.false2Notes receivable from Questar45false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse25false USDtruefalse$I2013Q2_dei_LegalEntityAxis_str_QuestarPipelineMember_us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxis_us-gaap_EstimateOfFairValueFairValueDisclosureMember_us-gaap_FairValueByFairValueHierarchyLevelAxis_us-gaap_FairValueInputsLevel2Memberhttp://www.sec.gov/CIK0000751652instant2013-06-30T00:00:000001-01-01T00:00:00falsefalseQuestar Pipeline [Member]dei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldistr_QuestarPipelineMemberdei_LegalEntityAxisexplicitMemberfalsefalseEstimated Fair Value [Member]us-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_EstimateOfFairValueFairValueDisclosureMemberus-gaap_FairValueByBalanceSheetGroupingDisclosureItemAmountsAxisexplicitMemberfalsefalseFair Value, Inputs, Level 2 [Member]us-gaap_FairValueByFairValueHierarchyLevelAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_FairValueInputsLevel2Memberus-gaap_FairValueByFairValueHierarchyLevelAxisexplicitMemberusdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Questar Pipeline [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]46true 4us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Financial liabilities [Abstract]47false 5us-gaap_LongTermDebtFairValueus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse508100000508.1USD$falsetruefalse2truefalsefalse536600000536.6USD$falsetruefalse3truefalsefalse535900000535.9USD$falsetruefalsexbrli:monetaryItemTypemonetaryThe fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.No definition available.false2Long-term debt, including current portionfalseFair Value Measurements (Details) (USD $)HundredThousandsUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.questar.com/role/FairValueMeasurementsDetails347