Name:	mga_EmployeeBenefitPlanForfeitedNonvestedAccountServiceBreakPeriod
Namespace Prefix:	mga_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the number of consecutive one-year breaks in service for forfeiture in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

Name:	mga_EmployeeBenefitPlanNumberOfConsecutiveOneYearBreaksInServiceForForfeiture
Namespace Prefix:	mga_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the age of participant for vested benefits distribution under employee benefit plan.

No definition available.

Name:	mga_EmployeeBenefitPlanParticipantAgeForVestedBenefitsDistribution
Namespace Prefix:	mga_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the number of continuous years of service for vested benefits distribution under employee benefit plan.

No definition available.

Name:	mga_EmployeeBenefitPlanVestedBenefitsDistributionPeriodOfContinuousYearsOfService
Namespace Prefix:	mga_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

Name:	us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of plan asset, in forfeited nonvested account, no longer allocated to participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478873/962-325-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (j)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

Name:	us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccount
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of decrease in forfeited nonvested account of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) from reallocation to participant.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (j)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-04(5)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1