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Post-Employment and Other Long-Term Employees Benefits - Pension Plan Asset Allocation (Parenthetical) (Detail)	Dec. 31, 2014
Corporate Bonds [Member]
Investment in funds, percentage	55.00%stm_DefinedBenefitPlanPlanAssetAllocationsInFunds / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CorporateBondSecuritiesMember
U.S.Treasury Bonds [Member]
Investment in funds, percentage	35.00%stm_DefinedBenefitPlanPlanAssetAllocationsInFunds / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasuryBondSecuritiesMember
Municipal Bonds [Member]
Investment in funds, percentage	10.00%stm_DefinedBenefitPlanPlanAssetAllocationsInFunds / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_MunicipalBondsMember

X

- Definition

Defined benefit plan, percentage of investment in funds.

+ References

No definition available.

+ Details

Name:	stm_DefinedBenefitPlanPlanAssetAllocationsInFunds
Namespace Prefix:	stm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_MunicipalBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_USTreasuryBondSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: