XML 100 R115.htm IDEA: XBRL DOCUMENT v3.20.1

Capital Stock - Maximum Number of Shares Outstanding Exercised or Converted (Detail) - Convertible Common Stock [Member] - Subsequent Event [Member]	Mar. 05, 2020 shares
Class of Stock [Line Items]
Common Shares	301,768,927
Stock options	9,745,110
Total number of shares outstanding	311,514,037

X

- Definition

Common shares and potentially dilutive securities outstanding.

+ References

No definition available.

+ Details

Name:	mga_CommonSharesAndPotentiallyDilutiveSecuritiesOutstanding
Namespace Prefix:	mga_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Potentially dilutive securities outstanding.

+ References

No definition available.

+ Details

Name:	mga_PotentiallyDilutiveSecuritiesOutstanding
Namespace Prefix:	mga_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

X

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

X

- Definition

Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_CommonStockSharesOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_ConvertibleCommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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