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Related Party Transactions - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Related Party Transaction [Line Items] |  |  |
Research and development expenses |  |  | $ 121.0
ST Foundation [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Contributed cash amounts to ST Foundation | $ 0.5 | $ 0.5 | 0.5
ST-Ericsson AT SA ("JVD") [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Research and development expenses |  |  | $ 121.0

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- Definition Research and development expenses from transactions with related party realized during the period. + References No definition available. + Details
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Namespace Prefix: | stm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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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
Name: | us-gaap_RelatedPartyTransactionLineItems
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
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=stm_StEricssonAtSAJvdMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |