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Other Income and Expenses, Net - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Other Income and Expenses [Abstract] |  |
Income recognition accrual amount | $ 33 | $ 0

X
- Definition Income recognition accrual amount. + References No definition available. + Details
Name: | stm_IncomeRecognitionAccrualAmount
Namespace Prefix: | stm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_OtherIncomeAndExpensesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration