XML 88 R96.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Long-Term Employee Benefit Liabilities - Asset Allocation of Defined Benefit Pension Plans (Detail) (Pension Plan, Defined Benefit [Member]) | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2014 Subsequent [Member] Minimum [Member] | Dec. 31, 2014 Subsequent [Member] Maximum [Member]
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Equity securities | 58.00% | 57.00% | 55.00% | 75.00%
Fixed income securities | 41.00% | 42.00% | 25.00% | 45.00%
Cash and cash equivalents | 1.00% | 1.00% | 0.00% | 15.00%
Total | 100.00% | 100.00% |  | 100.00%

X
- Definition Defined benefit plan cash and cash equivalents. + References No definition available. + Details
Name: | mga_DefinedBenefitPlanCashAndCashEquivalents
Namespace Prefix: | mga_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Defined benefit plans target allocation percentage. + References No definition available. + Details
Name: | mga_DefinedBenefitPlansTargetAllocationPercentage
Namespace Prefix: | mga_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Defined Benefit Plan Target Allocation Percentage Of Assets Debt Fixed Income Securities + References No definition available. + Details
Name: | mga_DefinedBenefitPlanTargetAllocationPercentageOfAssetsDebtFixedIncomeSecurities
Namespace Prefix: | mga_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e2446-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant