Other Expense, Net - Summary of Impairment Charges and Loss on Sale Recorded for Certain Investments (Detail) - Power & Vision [Member] $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($)
Impairments and loss on sale of equity-accounted investments [Line Items]
Impairments and loss on sale of equity-accounted investments	$ 347
Tax effect on Other expense, net	(53)
Loss attributable to non-controlling interests	(75)
Non-cash impairment charge included in Net income attributable to Magna International Inc.	219
Getrag (Jiangxi) Transmission Co., Ltd [GJT] [Member]
Impairments and loss on sale of equity-accounted investments [Line Items]
Impairment of equity-accounted investment	337
Dongfeng Getrag Transmission Co. Ltd ["DGT"] [Member]
Impairments and loss on sale of equity-accounted investments [Line Items]
Impairments and loss on sale of equity-accounted investments	$ 10

Gain loss on sale of equity method investments including impairment other.

No definition available.

Name:	mga_GainLossOnSaleOfEquityMethodInvestmentsIncludingImpairmentOtherThanTemporary
Namespace Prefix:	mga_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Impairment losses on equity method investments after tax attributable to parent.

No definition available.

Name:	mga_ImpairmentLossesOnEquityMethodInvestmentsAfterTaxAttributableToParent
Namespace Prefix:	mga_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Impairment losses on equity method investments attributable to non controlling interest.

No definition available.

Name:	mga_ImpairmentLossesOnEquityMethodInvestmentsAttributableToNonControllingInterest
Namespace Prefix:	mga_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Impairment of equity-accounted investment.

No definition available.

Name:	mga_ImpairmentOfEquityaccountedInvestment
Namespace Prefix:	mga_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Impairments And Loss On Sale Of Equity Accounted Investments

No definition available.

Name:	mga_ImpairmentsAndLossOnSaleOfEquityAccountedInvestmentsLineItems
Namespace Prefix:	mga_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Tax component of impairment losses of equity method investments.

No definition available.

Name:	mga_TaxComponentOfImpairmentLossesOfEquityMethodInvestments
Namespace Prefix:	mga_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Name:	us-gaap_StatementBusinessSegmentsAxis=mga_PowerAndVisionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=mga_GetragJiangxiTransmissionCoLtdMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=mga_DongfengGetragTransmissionCoLtdMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: