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Income Tax - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	0 Months Ended		12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Loss Carryforwards [Line Items]
Netherlands statutory income taxes rate			25.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	25.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	25.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Significant losses in countries subject to tax holidays				$ 57stm_SignificantLossesInCountriesSubjectToTaxHolidays	$ 320stm_SignificantLossesInCountriesSubjectToTaxHolidays
Valuation allowance adjustments			26us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	(83)us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	(197)us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance
Effect of the tax benefits on basic earnings per share			$ 0.07us-gaap_IncomeTaxHolidayIncomeTaxBenefitsPerShare	$ 0.02us-gaap_IncomeTaxHolidayIncomeTaxBenefitsPerShare	$ 0.04us-gaap_IncomeTaxHolidayIncomeTaxBenefitsPerShare
Maximum percentage of tax reduction from tax holidays			100.00%stm_MaximumPercentageOfTaxReductionFromTaxHolidays	100.00%stm_MaximumPercentageOfTaxReductionFromTaxHolidays	100.00%stm_MaximumPercentageOfTaxReductionFromTaxHolidays
Income tax holiday expiration date			Dec. 31, 2022
Legal inflationary index					0.53%stm_LegalInflationaryIndex
Deferred tax benefit (expense) recorded as component of other comprehensive income (loss)			24us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	(31)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax
Cumulative amount of distributable earnings	775us-gaap_RetainedEarningsUnappropriated		775us-gaap_RetainedEarningsUnappropriated
Unrecognized tax benefits	238stm_UnrecognizedTaxBenefitsAgainstExistingNetOperatingLosses	229stm_UnrecognizedTaxBenefitsAgainstExistingNetOperatingLosses	238stm_UnrecognizedTaxBenefitsAgainstExistingNetOperatingLosses	229stm_UnrecognizedTaxBenefitsAgainstExistingNetOperatingLosses
Accrued interest and penalties related to uncertain tax positions	27us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued		27us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued
Interest and penalties of unrecognized tax benefits	32us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense	6us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense
Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Open tax year			1996
Latest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Open tax year			2014
STE Deconsolidation [Member]
Operating Loss Carryforwards [Line Items]
Valuation allowance adjustments				$ 32us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance / us-gaap_RestructuringCostAndReserveAxis = stm_DeconsolidationMember

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Maximum Percentage of Tax reduction from Tax holidays.

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Significant losses in countries subject to tax holidays.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Per share amount effect of the income tax benefit resulting from the income tax holidays granted by taxing jurisdictions.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in the valuation allowance for deferred tax assets.

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Tax year that remains open to examination under enacted tax laws, in CCYY format.

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Amount of tax (expense) benefit, after reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans.

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A segregation of retained earnings which is available for dividend distribution. Earnings not paid out as dividends but instead reinvested in the core business or used to pay off debt. Unappropriated profit is part of shareholder equity. Also called cumulative distributions or earned surplus or accumulated earnings or unappropriated profit.

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