XML 67 R51.htm IDEA: XBRL DOCUMENT
v3.20.4

Decommissioning Liabilities (Details) - Provision for decommissioning, restoration and rehabilitation costs [member] - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Reconciliation of changes in other provisions [abstract] |  |
Beginning balance | $ 59.0 | $ 44.9
Reclamation expenditures |  | (2.0)
Accretion expense | 2.6 | 2.8
Reclamation, Care and Maintenance Expenses | 3.5 | 1.9
Revisions to expected discounted cash flows | 17.1 | 13.3
Ending balance | $ 75.2 | $ 59.0

X
- Definition Reclamation Expenses + References No definition available. + Details
Name: | agi_ReclamationExpenses
Namespace Prefix: | agi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The increase (decrease) in other provisions resulting from a change in discount rate. [Refer: Other provisions] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 37 -IssueDate 2020-01-01 -Paragraph 84 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=37&code=ifrs-tx-2020-en-r&anchor=para_84_e&doctype=Standard -URIDate 2020-01-01 + Details
Name: | ifrs-full_IncreaseDecreaseThroughChangeInDiscountRateOtherProvisions
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The increase in other provisions through adjustments arising from the passage of time. [Refer: Other provisions] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 37 -IssueDate 2020-01-01 -Paragraph 84 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=37&code=ifrs-tx-2020-en-r&anchor=para_84_e&doctype=Standard -URIDate 2020-01-01 + Details
Name: | ifrs-full_IncreaseDecreaseThroughTimeValueOfMoneyAdjustmentOtherProvisions
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The amount of provisions other than provisions for employee benefits. [Refer: Provisions] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 37 -IssueDate 2020-01-01 -Paragraph 84 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=37&code=ifrs-tx-2020-en-r&anchor=para_84_a&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 78 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_78_d&doctype=Standard -URIDate 2020-01-01 + Details
Name: | ifrs-full_OtherProvisions
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The amount used (ie incurred and charged against the provision) for other provisions. [Refer: Other provisions] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 37 -IssueDate 2020-01-01 -Paragraph 84 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=37&code=ifrs-tx-2020-en-r&anchor=para_84_c&doctype=Standard -URIDate 2020-01-01 + Details
Name: | ifrs-full_ProvisionUsedOtherProvisions
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | ifrs-full_ReconciliationOfChangesInOtherProvisionsAbstract
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | ifrs-full_ClassesOfProvisionsAxis=ifrs-full_ProvisionForDecommissioningRestorationAndRehabilitationCostsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |