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Warranty - Schedule of Company's Warranty Accruals (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Guarantees [Abstract]
Balance, beginning of year	$ 91us-gaap_ProductWarrantyAccrual	$ 94us-gaap_ProductWarrantyAccrual	$ 76us-gaap_ProductWarrantyAccrual
Expense, net	47mga_ProductWarrantyIncomeExpenseNet	40mga_ProductWarrantyIncomeExpenseNet	43mga_ProductWarrantyIncomeExpenseNet
Settlements	(40)us-gaap_ProductWarrantyAccrualPayments	(46)us-gaap_ProductWarrantyAccrualPayments	(46)us-gaap_ProductWarrantyAccrualPayments
Acquisitions [note 6]		1us-gaap_ProductWarrantyAccrualAdditionsFromBusinessAcquisition	17us-gaap_ProductWarrantyAccrualAdditionsFromBusinessAcquisition
Foreign exchange and other	(10)us-gaap_ProductWarrantyAccrualCurrencyTranslationIncreaseDecrease	2us-gaap_ProductWarrantyAccrualCurrencyTranslationIncreaseDecrease	4us-gaap_ProductWarrantyAccrualCurrencyTranslationIncreaseDecrease
Balance, end of year	$ 88us-gaap_ProductWarrantyAccrual	$ 91us-gaap_ProductWarrantyAccrual	$ 94us-gaap_ProductWarrantyAccrual

X

- Definition

Product warranty income expense net.

+ References

No definition available.

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- Details

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- Definition

Carrying value as of the balance sheet date of obligations incurred through that date and payable for estimated claims under standard and extended warranty protection rights granted to customers.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.15(5))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 15

-Subparagraph 5

-Article 9



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph ((c)(5))

-URI http://asc.fasb.org/extlink&oid=6398077&loc=d3e12565-110249

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X

- Definition

Total liability for standard and extended product warranties acquired in a business acquisition.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6398077&loc=d3e12565-110249

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- Definition

Total Increase or Decrease in the standard and extended product warranty liability due to currency translation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6398077&loc=d3e12565-110249

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- Definition

Represents the aggregate decrease in the liability related to payments to satisfy claims for standard and extended product warranties.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph ((c)(2))

-URI http://asc.fasb.org/extlink&oid=6398077&loc=d3e12565-110249

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