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Financial Instruments and Risk Management - Notional Amounts of Outstanding Derivative Instruments (Detail)
In Millions, unless otherwise specified
Dec. 31, 2014
Hedge on R&D and Other Operating Expense Forecasted [Member]
Foreign Exchange Forward [Member]
EUR (€)
Dec. 31, 2014
Hedge on R&D and Other Operating Expense Forecasted [Member]
Collars [Member]
EUR (€)
Dec. 31, 2014
Hedge on Manufacturing Cost Forecast [Member]
Foreign Exchange Forward [Member]
EUR (€)
Dec. 31, 2014
Hedge on Manufacturing Cost Forecast [Member]
Foreign Exchange Forward [Member]
SGD
Dec. 31, 2014
Hedge on Manufacturing Cost Forecast [Member]
Collars [Member]
EUR (€)
Derivative [Line Items]          
Notional amount € 211invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= stm_HedgeOnRdAndOtherOperatingExpenseForecastedMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeForwardMember		 € 221invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= stm_HedgeOnRdAndOtherOperatingExpenseForecastedMember
/ us-gaap_DerivativeInstrumentRiskAxis
= stm_CurrencyCollarsMember		 € 294invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= stm_HedgeOnManufacturingCostForecastMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeForwardMember		 136invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= stm_HedgeOnManufacturingCostForecastMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeForwardMember		 € 331invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= stm_HedgeOnManufacturingCostForecastMember
/ us-gaap_DerivativeInstrumentRiskAxis
= stm_CurrencyCollarsMember