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Interest Expense, Net - Additional Information (Detail) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Net Investment Income [Line Items]      
Capitalized borrowing cost $ 0us-gaap_InterestExpenseShortTermBorrowings $ 0us-gaap_InterestExpenseShortTermBorrowings $ 0us-gaap_InterestExpenseShortTermBorrowings
Senior Unsecured Convertible Debt [Member]      
Net Investment Income [Line Items]      
Interest expense 12,000,000us-gaap_InterestExpenseDebt
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= stm_SeniorUnsecuredConvertibleDebtMember		    
Non-cash interest expense accretion of discount on liability component 10,000,000us-gaap_AccretionExpense
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= stm_SeniorUnsecuredConvertibleDebtMember		    
Issued date of senior unsecured convertible bonds Jul. 31, 2014    
Floating Rate Notes [Member]      
Net Investment Income [Line Items]      
Interest income (expense), net $ 2,400,000us-gaap_InvestmentIncomeNet
/ us-gaap_InvestmentTypeAxis
= stm_FloatingRateNotesMember		 $ 1,000,000us-gaap_InvestmentIncomeNet
/ us-gaap_InvestmentTypeAxis
= stm_FloatingRateNotesMember		 $ 2,000,000us-gaap_InvestmentIncomeNet
/ us-gaap_InvestmentTypeAxis
= stm_FloatingRateNotesMember