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Investments - Company's Investment in ABCP (Detail) (ABCP [Member], USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
ABCP [Member] |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |
Balance, beginning of year | $ 90 | $ 82 | $ 84
Valuation adjustment | 8 | 15 | 0
Cash receipts | 0 | (9) | 0
Foreign exchange and other | (6) | 2 | (2)
Balance, end of year | $ 92 | $ 90 | $ 82

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- Definition Cash receipts. + References No definition available. + Details
Name: | mga_CashReceipts
Namespace Prefix: | mga_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Foreign exchange and other. + References No definition available. + Details
Name: | mga_ForeignExchangeAndOther
Namespace Prefix: | mga_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Investment Carrying Value. + References No definition available. + Details
Name: | mga_InvestmentCarryingValue
Namespace Prefix: | mga_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Valuation adjustment impairment. + References No definition available. + Details
Name: | mga_ValuationAdjustmentImpairment
Namespace Prefix: | mga_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_ScheduleOfEquityMethodInvestmentsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration