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v2.4.1.9

Goodwill - Goodwill by Segment (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013
Goodwill [Line Items] |  |
Goodwill, Beginning balance | $ 1,440 us-gaap_Goodwill | $ 1,473 us-gaap_Goodwill
Acquisitions | 3 us-gaap_GoodwillAcquiredDuringPeriod | 1 us-gaap_GoodwillAcquiredDuringPeriod
Impairments |  | (22)us-gaap_GoodwillImpairmentLoss
Foreign exchange and other | (93)us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments | (12)us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments
Goodwill, Ending balance | 1,350 us-gaap_Goodwill | 1,440 us-gaap_Goodwill
North America [Member] |  |
Goodwill [Line Items] |  |
Goodwill, Beginning balance | 656 us-gaap_Goodwill / us-gaap_StatementGeographicalAxis = us-gaap_NorthAmericaMember | 701 us-gaap_Goodwill / us-gaap_StatementGeographicalAxis = us-gaap_NorthAmericaMember
Acquisitions | 3 us-gaap_GoodwillAcquiredDuringPeriod / us-gaap_StatementGeographicalAxis = us-gaap_NorthAmericaMember | (24)us-gaap_GoodwillAcquiredDuringPeriod / us-gaap_StatementGeographicalAxis = us-gaap_NorthAmericaMember
Foreign exchange and other | (24)us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments / us-gaap_StatementGeographicalAxis = us-gaap_NorthAmericaMember | (21)us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments / us-gaap_StatementGeographicalAxis = us-gaap_NorthAmericaMember
Goodwill, Ending balance | 635 us-gaap_Goodwill / us-gaap_StatementGeographicalAxis = us-gaap_NorthAmericaMember | 656 us-gaap_Goodwill / us-gaap_StatementGeographicalAxis = us-gaap_NorthAmericaMember
Europe [Member] |  |
Goodwill [Line Items] |  |
Goodwill, Beginning balance | 655 us-gaap_Goodwill / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember | 611 us-gaap_Goodwill / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
Acquisitions |  | 22 us-gaap_GoodwillAcquiredDuringPeriod / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
Foreign exchange and other | (67)us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember | 22 us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
Goodwill, Ending balance | 588 us-gaap_Goodwill / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember | 655 us-gaap_Goodwill / us-gaap_StatementGeographicalAxis = us-gaap_EuropeMember
Asia [Member] |  |
Goodwill [Line Items] |  |
Goodwill, Beginning balance | 129 us-gaap_Goodwill / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember | 74 us-gaap_Goodwill / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember
Acquisitions |  | 3 us-gaap_GoodwillAcquiredDuringPeriod / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember
Reallocation between reporting segments |  | 51 us-gaap_GoodwillTransfers / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember
Foreign exchange and other | (2)us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember | 1 us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember
Goodwill, Ending balance | 127 us-gaap_Goodwill / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember | 129 us-gaap_Goodwill / us-gaap_StatementGeographicalAxis = us-gaap_AsiaMember
Rest of World [Member] |  |
Goodwill [Line Items] |  |
Goodwill, Beginning balance |  | 87 us-gaap_Goodwill / us-gaap_StatementGeographicalAxis = mga_RestOfWorldMember
Impairments |  | (22)us-gaap_GoodwillImpairmentLoss / us-gaap_StatementGeographicalAxis = mga_RestOfWorldMember
Reallocation between reporting segments |  | (51)us-gaap_GoodwillTransfers / us-gaap_StatementGeographicalAxis = mga_RestOfWorldMember
Foreign exchange and other |  | $ (14)us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments / us-gaap_StatementGeographicalAxis = mga_RestOfWorldMember

X
- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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- Definition Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13854-109267 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13777-109266 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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- Details
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- Definition Amount of transfers of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized among segments. + References No definition available. + Details
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Balance Type: | debit
Period Type: | duration

X
- Definition Amount of increase (decrease) from foreign currency translation adjustments and purchase accounting adjustments of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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Balance Type: | debit
Period Type: | duration

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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Namespace Prefix: |
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Balance Type: |
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