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Accounting Policies - Schedule of Property, Plant and Equipment Useful Lives (Detail) | 12 Months Ended
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Dec. 31, 2018
Buildings [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful lives of Property, Plant and Equipment, Average | 33 years
Facilities and Leasehold Improvements [Member] | Minimum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful lives of Property, Plant and Equipment, Average | 5 years
Facilities and Leasehold Improvements [Member] | Maximum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful lives of Property, Plant and Equipment, Average | 10 years
Machinery and Equipment [Member] | Minimum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful lives of Property, Plant and Equipment, Average | 2 years
Machinery and Equipment [Member] | Maximum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful lives of Property, Plant and Equipment, Average | 10 years
Computer and R&D Equipment [Member] | Minimum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful lives of Property, Plant and Equipment, Average | 3 years
Computer and R&D Equipment [Member] | Maximum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful lives of Property, Plant and Equipment, Average | 6 years
Other [Member] | Minimum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful lives of Property, Plant and Equipment, Average | 2 years
Other [Member] | Maximum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful lives of Property, Plant and Equipment, Average | 5 years

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=stm_ComputerAndResearchAndDevelopmentEquipmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_PropertyPlantAndEquipmentOtherTypesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |