Debt instrument redemption price amount.

No definition available.

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash outflow to reacquire common stock during the period.

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Name:	us-gaap_PaymentsForRepurchaseOfCommonStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of shares purchased for issuance under share-based payment arrangement.

+ References

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	duration

- Definition

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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Period Type:	duration

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mga_SeniorNotesRedemptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=mga_NotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Subsequent Event - Additional Information (Detail) $ in Millions, $ in Millions			12 Months Ended
	Feb. 28, 2022 USD ($) shares	Feb. 28, 2022 CAD ($) shares	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Cash consideration received in lieu of cancellation			$ 517	$ 203
Subsequent Event [Member]
Cancellation of common shares \| shares	1,600,500	1,600,500
Stock-based compensation awards, common shares \| shares	165,773	165,773
Cash consideration received in lieu of cancellation	$ 132
Subsequent Event [Member] \| Senior Notes Redemption [Member]
Debt Instrument, Face Amount		$ 425
Gain (Loss) on Extinguishment of Debt		5
Debt instrument redemption price amount		$ 430
Subsequent Event [Member] \| Notes [Member]
Senior note percentage		3.10%