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Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	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

X

- Definition

Cumulative probability threshold for realization of income tax benefits.

+ References

No definition available.

+ Details

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X

- Definition

Minimum recognizable tax benefit.

+ References

No definition available.

+ Details

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X

- Details

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X

- Definition

Sustainability Threshold for Uncertain Tax Position.

+ References

No definition available.

+ Details

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Namespace Prefix:	stm_
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X

- 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

X

- 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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X

- 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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- 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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X

- Details

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- Details

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X

- Details

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