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Marketable Securities - Changes in Value of Marketable Securities Reported in Current Assets on Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Marketable Securities [Line Items]
Beginning Balance	$ 330	$ 431
Purchase			$ 99
Proceeds at maturity	(200)	(100)
Change in fair value included in OCI	3	(1)
Ending Balance	133	330	431
U.S. Treasury Debt Securities [Member]
Marketable Securities [Line Items]
Beginning Balance	330	431
Proceeds at maturity	(200)	(100)
Change in fair value included in OCI	3	(1)
Ending Balance	$ 133	$ 330	$ 431

X

- Definition

Other comprehensive income loss marketable securities adjustment before tax.

+ References

No definition available.

+ Details

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Namespace Prefix:	stm_
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Balance Type:	credit
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X

- Definition

Amount of investment in marketable security, classified as current.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=118951113&loc=d3e6676-107765

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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X

- 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.

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X

- Definition

Amount of cash outflow for purchase of marketable security.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26853-111562

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X

- Definition

The cash inflow associated with the aggregate amount received by the entity through sale or maturity of marketable securities (held-to-maturity or available-for-sale) during the period.

+ References

No definition available.

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