Retirement plans - Asset allocation (Details)	Dec. 31, 2025	Dec. 31, 2024
Employee Benefits [Abstract]
Equity securities	24.00%	23.00%
Debt securities	16.00%	14.00%
Cash and other short-term securities	60.00%	63.00%
Total	100.00%	100.00%

The percentage cash and cash equivalents contribute to the fair value of defined benefit plan assets. [Refer: Cash and cash equivalents; Plan assets, at fair value; Defined benefit plans [domain]] [Contrast: Cash and cash equivalents, amount contributed to fair value of plan assets]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2025-01-01
-Paragraph 142
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_142_a&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_CashAndCashEquivalentsPercentageContributedToFairValueOfPlanAssets
Namespace Prefix:	ifrs-full_
Data Type:	dtr-2022:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage instruments representing debt (rather than equity) contribute to the fair value of defined benefit plan assets. [Refer: Plan assets, at fair value; Defined benefit plans [domain]] [Contrast: Debt instruments, amount contributed to fair value of plan assets]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2025-01-01
-Paragraph 142
-Subparagraph c
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_142_c&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_DebtInstrumentsPercentageContributedToFairValueOfPlanAssets
Namespace Prefix:	ifrs-full_
Data Type:	dtr-2022:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage equity instruments contribute to the fair value of defined benefit plan assets. [Refer: Plan assets, at fair value; Defined benefit plans [domain]] [Contrast: Equity instruments, amount contributed to fair value of plan assets]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2025-01-01
-Paragraph 142
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2025-en-r&anchor=para_142_b&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_EquityInstrumentsPercentageContributedToFairValueOfPlanAssets
Namespace Prefix:	ifrs-full_
Data Type:	dtr-2022:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Employee Benefits [Abstract]

+ References

No definition available.

+ Details

Name:	mx_EmployeeBenefitsAbstract
Namespace Prefix:	mx_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Plan Assets At Fair Value, Allocation Percentage

+ References

No definition available.

+ Details

Name:	mx_PlanAssetsAtFairValueAllocationPercentage
Namespace Prefix:	mx_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant