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Changes in Accumulated Other Comprehensive Income (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax $ 0us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax $ 0us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax 0us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesTax 1us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesTax
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax   0us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax   1us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax
Changes in Accumulated Other Comprehensive Income [Roll Forward]    
Accumulated Other Comprehensive Income (Loss), Net of Tax (21)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax (77)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
Other comprehensive income before reclassifications, net of tax (147)msc_OtherComprehensiveIncomeBeforeReclassificationsNetOfTax 37msc_OtherComprehensiveIncomeBeforeReclassificationsNetOfTax
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Reclassification Adjustments, Net of Tax (86)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeReclassificationAdjustmentsNetOfTax 50us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeReclassificationAdjustmentsNetOfTax
Amounts reclassified from Accumulated other comprehensive loss, net of tax 9msc_AmountsReclassifiedFromAccumulatedOtherComprehensiveLossNetOfTax 19msc_AmountsReclassifiedFromAccumulatedOtherComprehensiveLossNetOfTax
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax 0us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationReclassificationAdjustmentFromAOCIRealizedUponSaleOrLiquidationNetOfTax 0us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationReclassificationAdjustmentFromAOCIRealizedUponSaleOrLiquidationNetOfTax
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax   18us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansNetOfTax
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent (138)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent 56us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent
Accumulated Other Comprehensive Income (Loss), Net of Tax (159)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax (21)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
Pension Plan, Defined Benefit [Member]    
Changes in Accumulated Other Comprehensive Income [Roll Forward]    
Accumulated Other Comprehensive Income (Loss), Net of Tax (228)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ msc_ReclassificationsOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_PensionPlansDefinedBenefitMember		 (151)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ msc_ReclassificationsOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_PensionPlansDefinedBenefitMember
Foreign Currency Translation Gains Losses [Member]    
Changes in Accumulated Other Comprehensive Income [Roll Forward]    
Accumulated Other Comprehensive Income (Loss), Net of Tax 69us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ msc_ReclassificationsOutOfAccumulatedOtherComprehensiveIncomeAxis
= msc_ForeignCurrencyTranslationGainsLossesMember		 130us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ msc_ReclassificationsOutOfAccumulatedOtherComprehensiveIncomeAxis
= msc_ForeignCurrencyTranslationGainsLossesMember
Gains and Losses on Cash Flow Hedges [Member]    
Changes in Accumulated Other Comprehensive Income [Roll Forward]    
Accumulated Other Comprehensive Income (Loss), Net of Tax   (1)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= msc_GainsAndLossesOnCashFlowHedgesMember
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent   1us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= msc_GainsAndLossesOnCashFlowHedgesMember
Pension Plan, Defined Benefit [Member]    
Changes in Accumulated Other Comprehensive Income [Roll Forward]    
Accumulated Other Comprehensive Income (Loss), Net of Tax   (219)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_PensionPlansDefinedBenefitMember
Amounts reclassified from Accumulated other comprehensive loss, net of tax 9msc_AmountsReclassifiedFromAccumulatedOtherComprehensiveLossNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_PensionPlansDefinedBenefitMember		 18msc_AmountsReclassifiedFromAccumulatedOtherComprehensiveLossNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_PensionPlansDefinedBenefitMember
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent (77)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_PensionPlansDefinedBenefitMember		 68us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_PensionPlansDefinedBenefitMember
Income Tax Expense (Benefit) 0us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_PensionPlansDefinedBenefitMember		 (2)us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_PensionPlansDefinedBenefitMember
Amortization of prior service cost 0us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_PensionPlansDefinedBenefitMember		 [1] (1)us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_PensionPlansDefinedBenefitMember		 [1]
Amortization of net losses 9msc_AmortizationOfActuarialLosses
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_PensionPlansDefinedBenefitMember		 [1] 21msc_AmortizationOfActuarialLosses
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_PensionPlansDefinedBenefitMember		 [1]
Foreign Currency Translation Gains Losses [Member]    
Changes in Accumulated Other Comprehensive Income [Roll Forward]    
Accumulated Other Comprehensive Income (Loss), Net of Tax   143us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= msc_ForeignCurrencyTranslationGainsLossesMember
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent $ (61)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= msc_ForeignCurrencyTranslationGainsLossesMember		 $ (13)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= msc_ForeignCurrencyTranslationGainsLossesMember
[1] These accumulated other comprehensive income components are included in the computation of net pension and postretirement benefit expense (see Note 10).