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

X

- 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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