1.0.0.3 false CONSOLIDATED STATEMENTS OF INCOME (Unaudited) (USD $) In Millions, except Per Share data false 1 $ false false u000 Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 u001 Standard http://www.xbrl.org/2003/instance shares xbrli 0 u002 Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 false 2 $ false false u000 Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 u001 Standard http://www.xbrl.org/2003/instance shares xbrli 0 u002 Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 false 3 $ false false u000 Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 u001 Standard http://www.xbrl.org/2003/instance shares xbrli 0 u002 Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 false 4 $ false false u000 Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 u001 Standard http://www.xbrl.org/2003/instance shares xbrli 0 u002 Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 5 REVENUES 3 us-gaap_RevenuesAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false 4 false false 0 0 false false No definition available. false 6 Market Resources 4 us-gaap_OilAndGasRevenue us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 true true 474900000 474.9 false false 2 true true 601000000 601.0 false false 3 true true 1379200000 1379.2 false false 4 true true 1789600000 1789.6 false false No definition available. No authoritative reference available. false 7 Questar Pipeline 4 us-gaap_GasDomesticRegulatedRevenue us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 42600000 42.6 false false 2 false true 43800000 43.8 false false 3 false true 126300000 126.3 false false 4 false true 131800000 131.8 false false No definition available. No authoritative reference available. false 8 Questar Gas 4 us-gaap_RefiningAndMarketingRevenue us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 82300000 82.3 false false 2 false true 115200000 115.2 false false 3 false true 626500000 626.5 false false 4 false true 664900000 664.9 false false No definition available. No authoritative reference available. false 9 Total Revenues 4 us-gaap_Revenues us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 599800000 599.8 false false 2 false true 760000000 760.0 false false 3 false true 2132000000 2132.0 false false 4 false true 2586300000 2586.3 false false No definition available. No authoritative reference available. true 10 OPERATING EXPENSES 3 us-gaap_OperatingExpensesAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false 4 false false 0 0 false false No definition available. false 11 Cost of natural gas and other products sold (excluding operating expenses shown separately) 4 us-gaap_CostOfGoodsSoldOilAndGas us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 80200000 80.2 false false 2 false true 131200000 131.2 false false 3 false true 483600000 483.6 false false 4 false true 761800000 761.8 false false No definition available. No authoritative reference available. false 12 Operating and maintenance 4 us-gaap_CostOfPropertyRepairsAndMaintenance us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 78500000 78.5 false false 2 false true 93200000 93.2 false false 3 false true 263000000 263.0 false false 4 false true 271700000 271.7 false false No definition available. No authoritative reference available. false 13 General and administrative 4 us-gaap_GeneralAndAdministrativeExpense us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 47800000 47.8 false false 2 false true 34000000 34.0 false false 3 false true 136400000 136.4 false false 4 false true 121300000 121.3 false false No definition available. No authoritative reference available. false 14 Production and other taxes 4 us-gaap_TaxesOther us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 21400000 21.4 false false 2 false true 47600000 47.6 false false 3 false true 75300000 75.3 false false 4 false true 137700000 137.7 false false No definition available. No authoritative reference available. false 15 Depreciation, depletion and amortization 4 us-gaap_DepreciationAndAmortization us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 168600000 168.6 false false 2 false true 126000000 126.0 false false 3 false true 510000000 510.0 false false 4 false true 351900000 351.9 false false No definition available. No authoritative reference available. false 16 Exploration 4 us-gaap_ExplorationExpense us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 6300000 6.3 false false 2 false true 7400000 7.4 false false 3 false true 18300000 18.3 false false 4 false true 14700000 14.7 false false No definition available. No authoritative reference available. false 17 Abandonment and impairment 4 us-gaap_ExplorationAbandonmentAndImpairmentExpense us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 5100000 5.1 false false 2 false true 4100000 4.1 false false 3 false true 12600000 12.6 false false 4 false true 20900000 20.9 false false No definition available. No authoritative reference available. false 18 Total Operating Expenses 4 us-gaap_OperatingExpenses us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 407900000 407.9 false false 2 false true 443500000 443.5 false false 3 false true 1499200000 1499.2 false false 4 false true 1680000000 1680.0 false false No definition available. No authoritative reference available. true 19 Net gain (loss) from asset sales 3 us-gaap_GainLossOnDispositionOfAssets us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -300000 -0.3 false false 2 false true 59000000 59.0 false false 3 false true 1400000 1.4 false false 4 false true 62400000 62.4 false false No definition available. No authoritative reference available. false 20 OPERATING INCOME 3 us-gaap_OperatingIncomeLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 191600000 191.6 false false 2 false true 375500000 375.5 false false 3 false true 634200000 634.2 false false 4 false true 968700000 968.7 false false No definition available. No authoritative reference available. true 21 Interest and other income 3 us-gaap_InvestmentIncomeNonoperating us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 3600000 3.6 false false 2 false true 6700000 6.7 false false 3 false true 12300000 12.3 false false 4 false true 17000000 17.0 false false No definition available. No authoritative reference available. false 22 Income from unconsolidated affiliates 3 us-gaap_IncomeLossFromEquityMethodInvestments us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 1800000 1.8 false false 2 false true 900000 0.9 false false 3 false true 4800000 4.8 false false 4 false true 1300000 1.3 false false No definition available. No authoritative reference available. false 23 Net mark-to-market gain (loss) on basis-only swaps 3 us-gaap_UnrealizedGainLossOnDerivatives us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -10700000 -10.7 false false 2 false true -22500000 -22.5 false false 3 false true -173400000 -173.4 false false 4 false true 7500000 7.5 false false No definition available. No authoritative reference available. false 24 Interest expense 3 us-gaap_InterestExpense us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -31400000 -31.4 false false 2 false true -32800000 -32.8 false false 3 false true -93600000 -93.6 false false 4 false true -90900000 -90.9 false false No definition available. No authoritative reference available. false 25 INCOME BEFORE INCOME TAXES 3 us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 154900000 154.9 false false 2 false true 327800000 327.8 false false 3 false true 384300000 384.3 false false 4 false true 903600000 903.6 false false No definition available. No authoritative reference available. true 26 Income taxes 3 us-gaap_IncomeTaxExpenseBenefit us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -56100000 -56.1 false false 2 false true -121200000 -121.2 false false 3 false true -139300000 -139.3 false false 4 false true -334100000 -334.1 false false No definition available. No authoritative reference available. false 27 NET INCOME 3 us-gaap_ProfitLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 98800000 98.8 false false 2 false true 206600000 206.6 false false 3 false true 245000000 245.0 false false 4 false true 569500000 569.5 false false No definition available. No authoritative reference available. true 28 Net income attributable to noncontrolling interest 3 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -600000 -0.6 false false 2 false true -2400000 -2.4 false false 3 false true -1700000 -1.7 false false 4 false true -6900000 -6.9 false false No definition available. No authoritative reference available. false 29 NET INCOME ATTRIBUTABLE TO QUESTAR 3 us-gaap_NetIncomeLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 true true 98200000 98.2 false false 2 true true 204200000 204.2 false false 3 true true 243300000 243.3 false false 4 true true 562600000 562.6 false false No definition available. No authoritative reference available. true 30 EARNINGS PER COMMON SHARE ATTRIBUTABLE TO QUESTAR 3 us-gaap_EarningsPerShareAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false 4 false false 0 0 false false No definition available. false 31 Basic 4 us-gaap_EarningsPerShareBasic us-gaap true na duration decimal No definition available. false false false false false false false false true 1 true true 0.57 0.57 false false 2 true true 1.18 1.18 false false 3 true true 1.40 1.40 false false 4 true true 3.26 3.26 false false No definition available. No authoritative reference available. false 32 Diluted 4 us-gaap_EarningsPerShareDiluted us-gaap true na duration decimal No definition available. false false false false false false false false true 1 true true 0.56 0.56 false false 2 true true 1.16 1.16 false false 3 true true 1.38 1.38 false false 4 true true 3.19 3.19 false false No definition available. No authoritative reference available. false 33 Weighted Average Number Of Common Shares Outstanding 3 us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false 4 false false 0 0 false false No definition available. false 34 Used in basic calculation 4 us-gaap_WeightedAverageNumberOfSharesOutstandingBasic us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 174300000 174.3 false false 2 false true 172900000 172.9 false false 3 false true 174000000 174.0 false false 4 false true 172700000 172.7 false false No definition available. No authoritative reference available. false 35 Used in diluted calculation 4 us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 176300000 176.3 false false 2 false true 176100000 176.1 false false 3 false true 176100000 176.1 false false 4 false true 176200000 176.2 false false No definition available. No authoritative reference available. false 36 Dividends per common share 3 us-gaap_CommonStockDividendsPerShareCashPaid us-gaap true na duration decimal No definition available. false false false false false false false false true 1 true true 0.125 0.125 false false 2 true true 0.1225 0.1225 false false 3 true true 0.375 0.375 false false 4 true true 0.3675 0.3675 false false No definition available. No authoritative reference available. false false 4 32 false HundredThousands HundredThousands NoRounding false true