XML 144 R115.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Capital Stock - Summary of Normal Course Issuer Bids (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014
Schedule Of Share Repurchase Programs [Line Items] |  |
Shares purchased | 10,752,484 | 35,069,804
Cash amount | $ 501 | $ 1,766
2013 Bid [Member] |  |
Schedule Of Share Repurchase Programs [Line Items] |  |
Maximum number of shares | 40,000,000 |
Shares purchased |  | 30,271,428
Cash amount |  | $ 1,525
2014 Bid [Member] |  |
Schedule Of Share Repurchase Programs [Line Items] |  |
Maximum number of shares | 40,000,000 |
Shares purchased | 8,166,514 | 4,798,376
Cash amount | $ 388 | $ 241
2015 Bid [Member] |  |
Schedule Of Share Repurchase Programs [Line Items] |  |
Maximum number of shares | 40,000,000 |
Shares purchased | 2,585,970 |
Cash amount | $ 113 |

X
- Definition Cash Amount For Common Stock Repurchased Under Ncib + References No definition available. + Details
Name: | mga_CashAmountForCommonStockRepurchasedUnderNcib
Namespace Prefix: | mga_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Common stock repurchased during period shares. + References No definition available. + Details
Name: | mga_CommonStockRepurchasedDuringPeriodShares
Namespace Prefix: | mga_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Maximum Number of Common Stock Shares To Be Repurchased + References No definition available. + Details
Name: | mga_MaximumNumberOfCommonStockSharesToBeRepurchased
Namespace Prefix: | mga_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Schedule Of Share Repurchase Programs [Line Items] + References No definition available. + Details
Name: | mga_ScheduleOfShareRepurchaseProgramsLineItems
Namespace Prefix: | mga_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_PlanNameAxis=mga_TwoThousandThirteenBidMemberMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PlanNameAxis=mga_TwoThousandFourteenBidMemberMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PlanNameAxis=mga_TwoThousandFifteenBidMemberMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |