Debt Instrument Due Year

No definition available.

Name:	mga_DebtInstrumentDueYear
Namespace Prefix:	mga_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

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.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average interest rate of long-term debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_LongtermDebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

Debt - Schedule of Company's Long-Term Debt (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2016 CAD	Dec. 31, 2016 EUR (€)	Dec. 31, 2015
Three Point Six Two Five Senior Notes [Member]
Debt Instrument [Line Items]
Senior Notes, face amount	$ 750,000,000
Senior Notes, due year	2024
Interest rate	3.625%	3.625%	3.625%
Four Point One Five Zero Senior Notes [Member]
Debt Instrument [Line Items]
Senior Notes, face amount	$ 650,000,000
Senior Notes, due year	2025
Interest rate	4.15%	4.15%	4.15%
One Point Nine Zero Zero Senior Notes [Member]
Debt Instrument [Line Items]
Senior Notes, face amount \| €			€ 550,000,000
Senior Notes, due year	2023
Interest rate	1.90%	1.90%	1.90%
Three Point One Zero Zero Senior Notes [Member]
Debt Instrument [Line Items]
Senior Notes, face amount \| CAD		CAD 425,000,000
Senior Notes, due year	2022
Interest rate	3.10%	3.10%	3.10%
Bank Term Debt [Member]
Debt Instrument [Line Items]
Weighted average interest rate of bank term debt	7.30%	7.30%	7.30%	8.10%
Government Loans [Member]
Debt Instrument [Line Items]
Weighted average interest rate of bank term debt	2.53%	2.53%	2.53%	3.70%