Significant Accounting Policies - Concentration of Investments (Details) - The Magna Group of Companies Retirement Savings Plans - Employer's securities - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Significant Accounting Policies
Concentration of investment to total investments	$ 274	$ 231
Concentration of investment to total investments (as a percent)	10.00%	10.00%

Fair value of investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) as portion of total investments representing concentration risk at or above applicable threshold.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 275
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482861/275-10-50-18

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- Definition

Percentage of investment at fair value held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), to total investments representing concentration risk at or above applicable threshold.

+ References

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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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-02)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 962
-SubTopic 235
-Name Accounting Standards Codification
-Section S50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479143/962-235-S50-1

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