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Goodwill - Additional Information (Detail) (USD $) | 12 Months Ended | 3 Months Ended
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2014
Goodwill [Line Items] |  |  |
Accumulated impairment losses, net | $ 1,024,000,000us-gaap_GoodwillImpairedAccumulatedImpairmentLoss | $ 1,024,000,000us-gaap_GoodwillImpairedAccumulatedImpairmentLoss |
Impairment loss of goodwill | 0us-gaap_GoodwillImpairmentLoss | 38,000,000us-gaap_GoodwillImpairmentLoss |
Re-classification to AHFS |  | 10,000,000stm_GoodwillReclassifiedToAssetsHeldForSale |
Veredus [Member] |  |  |
Goodwill [Line Items] |  |  |
Minority interest ownership percentage |  | 67.00%us-gaap_MinorityInterestOwnershipPercentageByParent / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = stm_VeredusMember |
Re-classification to AHFS |  | 10,000,000stm_GoodwillReclassifiedToAssetsHeldForSale / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = stm_VeredusMember |
Sale of equity interest, percentage | 51.00%stm_PercentageOfEquityInterestSold / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = stm_VeredusMember |  |
Embedded Processing Solutions (EPS) [Member] |  |  |
Goodwill [Line Items] |  |  |
Accumulated impairment losses, net | 1,018,000,000us-gaap_GoodwillImpairedAccumulatedImpairmentLoss / us-gaap_StatementBusinessSegmentsAxis = stm_EmbeddedProcessingSolutionsMember | 1,018,000,000us-gaap_GoodwillImpairedAccumulatedImpairmentLoss / us-gaap_StatementBusinessSegmentsAxis = stm_EmbeddedProcessingSolutionsMember |
Impairment loss of goodwill |  | 38,000,000us-gaap_GoodwillImpairmentLoss / us-gaap_StatementBusinessSegmentsAxis = stm_EmbeddedProcessingSolutionsMember |
Embedded Processing Solutions (EPS) [Member] | Microcontrollers, Memory & Security ("MMS") [Member] |  |  |
Goodwill [Line Items] |  |  |
Impairment loss of goodwill |  |  | 0us-gaap_GoodwillImpairmentLoss / us-gaap_StatementBusinessSegmentsAxis = stm_EmbeddedProcessingSolutionsMember / us-gaap_SubsegmentsAxis = stm_MicrocontrollersNonFlashNonVolatileMemoryAndSmartCardProductsMember
Others [Member] |  |  |
Goodwill [Line Items] |  |  |
Accumulated impairment losses, net | 6,000,000us-gaap_GoodwillImpairedAccumulatedImpairmentLoss / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember | 6,000,000us-gaap_GoodwillImpairedAccumulatedImpairmentLoss / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember |
Digital Convergence Group ("DCG") [Member] |  |  |
Goodwill [Line Items] |  |  |
Impairment loss of goodwill |  | $ 38,000,000us-gaap_GoodwillImpairmentLoss / us-gaap_StatementBusinessSegmentsAxis = stm_DigitalConvergenceGroupMember |

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- Definition Goodwill Reclassified To Assets Held For Sale + References No definition available. + Details
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- Definition Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a,h) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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- Definition Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13854-109267 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13777-109266 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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- Definition The parent entity's interest in net assets of the subsidiary, expressed as a percentage. + References No definition available. + Details
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