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Other Non-Current Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Non-current assets sold without recourse	$ 118,000,000	$ 127,000,000
Minimum [Member]
Long-term receivables expected collection period	1 year
Maximum [Member]
Non-current assets sold , cost	$ 1,000,000	$ 1,000,000

X

- Definition

Amount of non current assets sold without recourse.

+ References

No definition available.

+ Details

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Namespace Prefix:	stm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Cost of non current assets sold without recourse.

+ References

No definition available.

+ Details

Name:	stm_CostOfNonCurrentAssetsSoldWithoutRecourse
Namespace Prefix:	stm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Long Term Receivables Collection Period

+ References

No definition available.

+ Details

Name:	stm_LongTermReceivablesCollectionPeriod
Namespace Prefix:	stm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: