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Segmented Information - Summary of External Revenues by Automotive Products and Services (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Segment Reporting Information [Line Items] |  |  |
Revenue from external customers | $ 36,641 us-gaap_Revenues | $ 34,835 us-gaap_Revenues | $ 30,837 us-gaap_Revenues
Exterior and Interior Systems [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue from external customers | 12,840 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_ExteriorAndInteriorSystemsMember | 12,308 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_ExteriorAndInteriorSystemsMember | 11,673 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_ExteriorAndInteriorSystemsMember
Body Systems and Chassis Systems [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue from external customers | 8,079 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_BodySystemsAndChassisSystemsMember | 7,874 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_BodySystemsAndChassisSystemsMember | 7,123 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_BodySystemsAndChassisSystemsMember
Powertrain Systems [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue from external customers | 4,954 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_PowertrainSystemsMember | 4,634 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_PowertrainSystemsMember | 3,825 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_PowertrainSystemsMember
Complete Vehicle Assembly [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue from external customers | 3,067 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_CompleteVehicleAssemblyMember | 3,062 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_CompleteVehicleAssemblyMember | 2,561 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_CompleteVehicleAssemblyMember
Tooling, Engineering and Other [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue from external customers | 2,971 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_ToolingEngineeringAndOtherMember | 2,823 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_ToolingEngineeringAndOtherMember | 2,317 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_ToolingEngineeringAndOtherMember
Vision and Electronic Systems [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue from external customers | 2,644 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_VisionAndElectronicSystemsMember | 2,193 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_VisionAndElectronicSystemsMember | 2,132 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_VisionAndElectronicSystemsMember
Closure Systems [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue from external customers | $ 2,086 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_ClosureSystemsMember | $ 1,941 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_ClosureSystemsMember | $ 1,206 us-gaap_Revenues / us-gaap_ProductOrServiceAxis = mga_ClosureSystemsMember

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- Definition Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Article 5 + Details
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