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Long-Term Employee Benefit Liabilities (Details 3) (Termination and long service arrangements [Member])	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Termination and long service arrangements [Member]
Weighted average significant actuarial assumptions used in measuring termination and long service arrangements
Discount rate	5.40%	4.90%	6.20%
Rate of compensation increase	4.00%	3.90%	4.10%

X

- Definition

Discount rate adopted in measuring projected termination and long service obligations and net periodic benefit cost.

+ References

No definition available.

+ Details

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Namespace Prefix:	mga_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Rate of compensation increase adopted in measuring projected termination and long service obligations and net periodic benefit cost.

+ References

No definition available.

+ Details

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Namespace Prefix:	mga_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

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