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Post-Employment and Other Long-Term Employees Benefits - Pension Plan Asset Allocation (Parenthetical) (Detail) | Dec. 31, 2014
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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

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- 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: |

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- 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: |