Income Taxes (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary of deferred income taxes provided on temporary differences
Tax depreciation greater (less) than book depreciation	$ 51	$ (13)	$ (7)
Book amortization in excess of tax amortization		(20)	(9)
Liabilities currently (not deductible) deductible for tax	(28)	(27)	14
Net tax losses (benefited) utilized	(37)	48	(23)
Change in valuation allowance on deferred tax assets	(78)	(3)
Other	16	(2)	13
Deferred income tax, Total	$ (76)	$ (17)	$ (12)

Future income tax expense benefit.

No definition available.

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

- Definition

Income tax reconciliation liabilities currently not deductible for tax.

+ References

No definition available.

+ Details

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

- Definition

Income tax reconciliation net tax losses utilized.

+ References

No definition available.

+ Details

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

- Details

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

- Definition

The portion of the difference between total income tax expense or benefit as reported in the Income Statement and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to changes in the valuation allowance for deferred tax assets in the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 45

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6907571&loc=d3e32123-109318

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 109

-Paragraph 26

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319

+ Details

Name:	us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to the different amortization methods allowed under generally accepted accounting principles and enacted tax laws.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319

+ Details

Name:	us-gaap_IncomeTaxReconciliationNondeductibleExpenseAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to the different depreciation methods allowed under generally accepted accounting principles and enacted tax laws.

+ References

+ Details

Name:	us-gaap_IncomeTaxReconciliationNondeductibleExpenseDepreciation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The portion of the difference, between total income tax expense or benefit as reported in the Income Statement for the year/accounting period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations, that is attributable to all other items not otherwise listed in the existing taxonomy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319

+ Details

Name:	us-gaap_IncomeTaxReconciliationOtherAdjustments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration