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Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Summary Of Accounting Policies [Line Items] |  |  |
Cumulative probability threshold for realization of income tax benefits | 50.00%stm_CumulativeProbabilityThresholdForRealizationOfIncomeTaxBenefits |  |
Minimum recognizable tax benefit | 50.00%stm_MinimumRecognizableTaxBenefit |  |
Sustainability threshold for uncertain tax position | 50.00%stm_SustainabilityThresholdForUncertainTaxPosition |  |
Employees average service period to grant awards | 3 years |  |
Advertising expenses | $ 8us-gaap_AdvertisingExpense | $ 11us-gaap_AdvertisingExpense | $ 12us-gaap_AdvertisingExpense
Minimum [Member] |  |  |
Summary Of Accounting Policies [Line Items] |  |  |
Equity investments, Ownership percentage | 20.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_RangeAxis = us-gaap_MinimumMember |  |
Maximum [Member] |  |  |
Summary Of Accounting Policies [Line Items] |  |  |
Equity investments, Ownership percentage | 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_RangeAxis = us-gaap_MaximumMember |  |
Trademarks and Licenses [Member] | Minimum [Member] |  |  |
Summary Of Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangible assets | 3 years |  |
Trademarks and Licenses [Member] | Maximum [Member] |  |  |
Summary Of Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangible assets | 7 years |  |
Capitalized Software [Member] | Maximum [Member] |  |  |
Summary Of Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangible assets | 4 years |  |

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- Definition Cumulative probability threshold for realization of income tax benefits. + References No definition available. + Details
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- Definition Minimum recognizable tax benefit. + References No definition available. + Details
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Balance Type: | na
Period Type: | duration

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- Details
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- Definition Sustainability Threshold for Uncertain Tax Position. + References No definition available. + Details
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- Definition Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 720 -SubTopic 35 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6420018&loc=d3e36677-107848 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571 + Details
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- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Details
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- Details
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- Details
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- Details
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