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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	$ 36,641us-gaap_Revenues	$ 34,835us-gaap_Revenues	$ 30,837us-gaap_Revenues
General Motors [Member]
Revenue from External Customer [Line Items]
Revenue from external customers	6,734us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_GeneralMotorsMember	6,394us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_GeneralMotorsMember	5,704us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_GeneralMotorsMember
Fiat or Chrysler Group [Member]
Revenue from External Customer [Line Items]
Revenue from external customers	5,897us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_FiatOrChryslerGroupMember	5,137us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_FiatOrChryslerGroupMember	4,637us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_FiatOrChryslerGroupMember
Ford Motor Company [Member]
Revenue from External Customer [Line Items]
Revenue from external customers	4,714us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_FordMotorCompanyMember	4,450us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_FordMotorCompanyMember	3,848us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_FordMotorCompanyMember
BMW [Member]
Revenue from External Customer [Line Items]
Revenue from external customers	4,649us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_BmwMember	4,882us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_BmwMember	4,100us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_BmwMember
Daimler AG [Member]
Revenue from External Customer [Line Items]
Revenue from external customers	4,262us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_DaimlerAgMember	3,949us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_DaimlerAgMember	3,367us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_DaimlerAgMember
Volkswagen [Member]
Revenue from External Customer [Line Items]
Revenue from external customers	4,144us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_VolkswagenMember	4,047us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_VolkswagenMember	3,835us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_VolkswagenMember
Other Customers [Member]
Revenue from External Customer [Line Items]
Revenue from external customers	$ 6,241us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_OtherCustomersMember	$ 5,976us-gaap_Revenues / us-gaap_MajorCustomersAxis = mga_OtherCustomersMember	$ 5,346us-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

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