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Income Tax - Reconciliation of Beginning and Ending Amounts of Unrecognized Tax Benefits (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 255us-gaap_UnrecognizedTaxBenefits	$ 227us-gaap_UnrecognizedTaxBenefits	$ 148us-gaap_UnrecognizedTaxBenefits
Additions based on tax positions related to the current year	51us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	52us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	44us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions
Additions for tax positions of prior years	43us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	27us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	39us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions
Reduction for tax positions of prior years	(2)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	(48)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions
Reduction due to ST-Ericsson deconsolidation		(8)stm_UnrecognizedTaxBenefitsDecreasesResultingFromDeconsolidation
Settlements			(1)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities
Prepayment	(5)stm_UnrecognizedTaxBenefitsRecordedInOtherAsset	(1)stm_UnrecognizedTaxBenefitsRecordedInOtherAsset	(6)stm_UnrecognizedTaxBenefitsRecordedInOtherAsset
Foreign currency translation	(29)stm_UnrecognizedTaxBenefitsIncreasesDecreaseResultingFromForeignCurrencyTranslation	6stm_UnrecognizedTaxBenefitsIncreasesDecreaseResultingFromForeignCurrencyTranslation	3stm_UnrecognizedTaxBenefitsIncreasesDecreaseResultingFromForeignCurrencyTranslation
Balance at end of year	$ 313us-gaap_UnrecognizedTaxBenefits	$ 255us-gaap_UnrecognizedTaxBenefits	$ 227us-gaap_UnrecognizedTaxBenefits

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- Definition

Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Unrecognized Tax Benefit

-URI http://asc.fasb.org/extlink&oid=6527854



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

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- Definition

Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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-Publisher FASB

-Name Accounting Standards Codification

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-Section 50

-Paragraph 15A

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

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