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Post-Employment and Other Long-Term Employees Benefits - Accumulated Other Comprehensive Income (Loss) Before Tax Effects (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]    
Other comprehensive loss, actuarial (gains)/losses, beginning balance $ 91us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax $ 209us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax
Net amount generated/arising in current year, actuarial (gains)/losses 76us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax (105)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax
Amortization, actuarial (gains)/losses (5)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax (15)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax
Foreign currency translation, actuarial (gains)/losses before tax (10)stm_OtherComprehensiveIncomeOfDefinedBenefitPlanForeignCurrencyTranslationForActuarialGainsLossesBeforeTax 2stm_OtherComprehensiveIncomeOfDefinedBenefitPlanForeignCurrencyTranslationForActuarialGainsLossesBeforeTax
Other comprehensive loss, actuarial (gains)/losses, ending balance 152us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax 91us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax
Other comprehensive loss, prior service cost, beginning balance 9us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax 9us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax
Net amount generated/arising in current year, prior service cost   5us-gaap_OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostCreditArisingDuringPeriodBeforeTax
Amortization, prior service cost (1)us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax (5)us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax
Foreign currency translation adjustment, prior service cost (1)us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesPlanAssets  
Other comprehensive loss, prior service cost, ending balance 7us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax 9us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax
Other comprehensive loss, Total, beginning balance 100us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax 218us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
Net amount generated/arising in current year, Total 76stm_OtherComprehensiveIncomeNetGainLossGeneratedArisingBeforeTax (100)stm_OtherComprehensiveIncomeNetGainLossGeneratedArisingBeforeTax
Amortization, Total (6)stm_OtherComprehensiveIncomeAmortizationOfDefinedBenefitPlanBeforeTax (20)stm_OtherComprehensiveIncomeAmortizationOfDefinedBenefitPlanBeforeTax
Foreign currency translation adjustment, Total (11)stm_OtherComprehensiveIncomeOfDefinedBenefitPlanForeignCurrencyTranslationBeforeTax 2stm_OtherComprehensiveIncomeOfDefinedBenefitPlanForeignCurrencyTranslationBeforeTax
Other comprehensive loss, Total, ending balance $ 159us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax $ 100us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax