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Segmented Information - Schedule of Aggregates External Revenues by Customer (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Revenue from External Customer [Line Items] |  |  |
Revenue from external customers | $ 36,641 us-gaap_Revenues | $ 34,835 us-gaap_Revenues | $ 30,837 us-gaap_Revenues
General Motors [Member] |  |  |
Revenue from External Customer [Line Items] |  |  |
Revenue from external customers | 6,734 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_GeneralMotorsMember | 6,394 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_GeneralMotorsMember | 5,704 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_GeneralMotorsMember
Fiat or Chrysler Group [Member] |  |  |
Revenue from External Customer [Line Items] |  |  |
Revenue from external customers | 5,897 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_FiatOrChryslerGroupMember | 5,137 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_FiatOrChryslerGroupMember | 4,637 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_FiatOrChryslerGroupMember
Ford Motor Company [Member] |  |  |
Revenue from External Customer [Line Items] |  |  |
Revenue from external customers | 4,714 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_FordMotorCompanyMember | 4,450 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_FordMotorCompanyMember | 3,848 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_FordMotorCompanyMember
BMW [Member] |  |  |
Revenue from External Customer [Line Items] |  |  |
Revenue from external customers | 4,649 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_BmwMember | 4,882 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_BmwMember | 4,100 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_BmwMember
Daimler AG [Member] |  |  |
Revenue from External Customer [Line Items] |  |  |
Revenue from external customers | 4,262 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_DaimlerAgMember | 3,949 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_DaimlerAgMember | 3,367 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_DaimlerAgMember
Volkswagen [Member] |  |  |
Revenue from External Customer [Line Items] |  |  |
Revenue from external customers | 4,144 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_VolkswagenMember | 4,047 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_VolkswagenMember | 3,835 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_VolkswagenMember
Other Customers [Member] |  |  |
Revenue from External Customer [Line Items] |  |  |
Revenue from external customers | $ 6,241 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_OtherCustomersMember | $ 5,976 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_OtherCustomersMember | $ 5,346 us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_OtherCustomersMember

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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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