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Financial Instruments and Risk Management - Effect on Consolidated Statements of Income of Derivative Instruments Not Designated as Hedge (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Derivative Instruments, Gain (Loss) [Line Items]    
Foreign exchange forward contracts $ 10us-gaap_DerivativeGainLossOnDerivativeNet $ 10us-gaap_DerivativeGainLossOnDerivativeNet
Forward Contracts [Member] | Other Income and Expenses, Net [Member] | Not Designated as Hedging Instrument [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Foreign exchange forward contracts $ 10us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForwardContractsMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_NondesignatedMember
/ us-gaap_IncomeStatementLocationAxis
= stm_OtherIncomeAndExpensesNetMember		 $ 10us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForwardContractsMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_NondesignatedMember
/ us-gaap_IncomeStatementLocationAxis
= stm_OtherIncomeAndExpensesNetMember