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Financial Instruments and Risk Management - Schedule of Assets (Liabilities) Measured at Fair Value on Non-Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) (Fair Value, Inputs, Level 3 [Member], USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets held for sale $ 11stm_FairValueMeasurementWithUnobservableInputsReconciliationNonrecurringBasisAssetAssetsHeldForSale  
Sale of assets (5)stm_FairValueMeasurementWithUnobservableInputsReconciliationNonrecurringBasisAssetSales  
Deconsolidation of assets (6)stm_FairValueMeasurementWithUnobservableInputsReconciliationNonrecurringBasisAssetDeconsolidationOfAssets  
Veredus asset group 16stm_FairValueMeasurementWithUnobservableInputsReconciliationNonrecurringBasisAssetPurchases  
Ending balance 16stm_FairValueMeasurementWithUnobservableInputsReconciliationNonecurringBasisAssetValue  
Amount of total losses for the period included in earnings attributable to assets still held at the reporting date (5)stm_FairValueMeasurementWithUnobservableInputsReconciliationNonRecurringBasisAssetStillHeldGainLossIncludedInEarningsAtReportingDate (3)stm_FairValueMeasurementWithUnobservableInputsReconciliationNonRecurringBasisAssetStillHeldGainLossIncludedInEarningsAtReportingDate
Veredus [Member]
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Sale of assets   (16)stm_FairValueMeasurementWithUnobservableInputsReconciliationNonrecurringBasisAssetSales
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= stm_VeredusMember
Veredus cost-method investment   3stm_FairValueMeasurementWithUnobservableInputsReconciliationNonrecurringBasisCostMethodInvestments
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= stm_VeredusMember
Other-then-temporary impairment on Veredus cost-method investment   $ (3)stm_FairValueMeasurementWithUnobservableInputsReconciliationNonRecurringBasisOtherThanTemporaryImpairmentOnEquitySecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= stm_VeredusMember