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Financial Instruments and Risk Management - Notional Amounts of Outstanding Derivative Instruments (Detail) - Dec. 31, 2020 - Designated as Hedging Instrument [Member] | EUR (€) | SGD ($)
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Foreign Exchange Forward Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount of Derivative Instruments | € 215,000,000 |
Notional amount of Derivative Instruments | 341,000,000 | $ 157,000,000
Currency Collars [Member] |  |
Derivative [Line Items] |  |
Notional amount of Derivative Instruments | 237,000,000 |
Notional amount of Derivative Instruments | € 334,000,000 |

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- Definition Derivative notional Amount for hedge on forecasted manufacturing costs. + References No definition available. + Details
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Namespace Prefix: | stm_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

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- Definition Derivative notional amount for hedge on forecasted research and development and other operating expenses. + References No definition available. + Details
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Namespace Prefix: | stm_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

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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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- Details
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Namespace Prefix: |
Data Type: | na
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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_DerivativeInstrumentRiskAxis=stm_CurrencyCollarsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |