v3.26.1

Commitments (Details) - USD ($) $ in Millions	12 Months Ended
Commitments (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Commitments [Line Items]
Royalties	$ 27.0	$ 13.8

X

- Definition

[Line Items] for Commitments [Table]

+ References

No definition available.

+ Details

Name:	agi_CommitmentsLineItems
Namespace Prefix:	agi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Note Expiry date 2027-01-01
-Name IAS
-Number 1
-IssueDate 2025-01-01
-Paragraph 85
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2025-en-b&anchor=para_85&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_RoyaltyExpense
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration