XML 99 R58.htm IDEA: XBRL DOCUMENT
v3.21.1

Other Expense, Net - Summary of Impairment Charges and Loss on Sale Recorded for Certain Investments (Parenthetical) (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Impairments and loss on sale of equity-accounted investments [Line Items] |  |
Impairment and loss on sale of equity-accounted investment | $ 347 | $ 700
Power & Vision [Member] |  |
Impairments and loss on sale of equity-accounted investments [Line Items] |  |
Impairment and loss on sale of equity-accounted investment | 347 | 700
Power & Vision [Member] | Dongfeng Getrag Transmission Co. Ltd ["DGT"] [Member] |  |
Impairments and loss on sale of equity-accounted investments [Line Items] |  |
Impairment and loss on sale of equity-accounted investment | $ 10 | $ 39
Ownership percentage |  | 50.00%

X
- Definition Impairments And Loss On Sale Of Equity Accounted Investments + References No definition available. + Details
Name: | mga_ImpairmentsAndLossOnSaleOfEquityAccountedInvestmentsLineItems
Namespace Prefix: | mga_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571 + Details
Name: | us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting. + References Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 + Details
Name: | us-gaap_GainLossOnInvestmentsExcludingOtherThanTemporaryImpairments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=mga_PowerAndVisionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=mga_DongfengGetragTransmissionCoLtdMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |