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Shareholders' Equity - Summary of Stock Option Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Stockholders' Equity [Abstract]
Outstanding shares, beginning balance	8,290,251us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	16,690,472us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	26,453,152us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Options forfeited, shares	(8,285,951)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod	(8,400,221)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod	(9,762,680)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
Outstanding shares, ending balance	4,300us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	8,290,251us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	16,690,472us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Stock option plans, Lower price range, Beginning Outstanding options	$ 16.73stm_NotionalAmountOfForeignCurrencyCashFlowHedgeDerivativesShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit	$ 16.73stm_NotionalAmountOfForeignCurrencyCashFlowHedgeDerivativesShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit	$ 16.73stm_NotionalAmountOfForeignCurrencyCashFlowHedgeDerivativesShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit
Stock option plans, Upper price range, Beginning Outstanding options	$ 27.21stm_NotionalAmountOfForeignCurrencyCashFlowHedgeDerivativesShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit	$ 27.21stm_NotionalAmountOfForeignCurrencyCashFlowHedgeDerivativesShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit	$ 33.70stm_NotionalAmountOfForeignCurrencyCashFlowHedgeDerivativesShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit
Options forfeited, Lower Range, Price Per Share	$ 16.73stm_StockOptionPlansOptionsForfeitedLowerRangePricePerShare	$ 16.73stm_StockOptionPlansOptionsForfeitedLowerRangePricePerShare	$ 17.08stm_StockOptionPlansOptionsForfeitedLowerRangePricePerShare
Options forfeited, Upper Range, Price Per Share	$ 27.21stm_StockOptionPlansOptionsForfeitedUpperRangePricePerShare	$ 27.21stm_StockOptionPlansOptionsForfeitedUpperRangePricePerShare	$ 33.70stm_StockOptionPlansOptionsForfeitedUpperRangePricePerShare
Stock option plans, Lower price range, Ending Outstanding options	$ 16.73stm_NotionalAmountOfForeignCurrencyCashFlowHedgeDerivativesShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit	$ 16.73stm_NotionalAmountOfForeignCurrencyCashFlowHedgeDerivativesShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit	$ 16.73stm_NotionalAmountOfForeignCurrencyCashFlowHedgeDerivativesShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit
Stock option plans, Upper price range, Ending Outstanding options	$ 16.73stm_NotionalAmountOfForeignCurrencyCashFlowHedgeDerivativesShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit	$ 27.21stm_NotionalAmountOfForeignCurrencyCashFlowHedgeDerivativesShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit	$ 27.21stm_NotionalAmountOfForeignCurrencyCashFlowHedgeDerivativesShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit
Outstanding, Weighted Average Price Per Share, beginning	$ 22.64us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	$ 21.00us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	$ 24.51us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
Options forfeited, Weighted Average Price Per Share	$ 22.65us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice	$ 19.39us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice	$ 30.50us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice
Outstanding, Weighted Average Price Per Share, ending	$ 16.73us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	$ 22.64us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	$ 21.00us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice

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- Definition

Notional Amount Of Foreign Currency Cash Flow Hedge Derivatives Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Lower Range Limit.

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Notional Amount Of Foreign Currency Cash Flow Hedge Derivatives Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Upper Range Limit.

+ References

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Stock option plans, options forfeited, lower range, price per share.

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- Definition

The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iv)(3)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Number of options outstanding, including both vested and non-vested options.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(i)-(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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