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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

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- 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

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- References

No definition available.

+ Details

Name:	us-gaap_OtherIncomeAndExpensesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration