XML 20 R81.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Financial Instruments and Risk Management (Hedging Instruments Recorded in AOCI) (Details) - Currency risk [member] - Fair value hedges [member] - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Reconciliation of changes in allowance account for credit losses of financial assets [abstract] |  |
Balance, beginning of the period | $ (1.4) | $ 6.0
Unrealized (loss) gains on currency instruments | 9.6 | (5.9)
Deferred income tax related to hedging instrument | (2.1) | 2.4
Balance, June 30, 2017 | 4.6 | (1.4)
CAD Currency Instruments [Member] |  |
Reconciliation of changes in allowance account for credit losses of financial assets [abstract] |  |
Unrealized (loss) gains on currency instruments | 0.0 | (3.9)
MXN Currency Instruments [Member] |  |
Reconciliation of changes in allowance account for credit losses of financial assets [abstract] |  |
Unrealized (loss) gains on currency instruments | $ (1.5) | $ 0.0

X
- Definition The amount of an allowance account used to record impairments to financial assets due to credit losses. [Refer: Financial assets] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2021-01-01 -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 16 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2017-en-b&anchor=para_16&doctype=Standard&book=b -URIDate 2019-03-27 + Details
Name: | ifrs-full_AllowanceAccountForCreditLossesOfFinancialAssets
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The amount of income tax relating to amounts recognised in other comprehensive income in relation to hedges of investments in equity instruments that the entity has designated at fair value through other comprehensive income. [Refer: Other comprehensive income; Reserve of gains and losses on hedging instruments that hedge investments in equity instruments] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2019-01-01 -Paragraph 81 -Subparagraph ab -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_81_ab&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 90 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_90&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_IncomeTaxRelatingToHedgesOfInvestmentsInEquityInstrumentsOfOtherComprehensiveIncome
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The increase (decrease) in an allowance account for credit losses of financial assets resulting from the net exchange differences arising when the financial statements are translated from the functional currency into a different presentation currency, including the translation of a foreign operation into the presentation currency of the reporting entity. [Refer: Allowance account for credit losses of financial assets] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Note Expiry date 2021-01-01 -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 16 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2017-en-b&anchor=para_16&doctype=Standard&book=b -URIDate 2019-03-27 + Details
Name: | ifrs-full_IncreaseDecreaseThroughNetExchangeDifferencesAllowanceAccountForCreditLossesOfFinancialAssets
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

X
- Details
Name: | ifrs-full_TypesOfRisksAxis=ifrs-full_CurrencyRiskMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TypesOfHedgesAxis=ifrs-full_FairValueHedgesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_HedgedItemsAxis=agi_CADCurrencyInstrumentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_HedgedItemsAxis=agi_MXNCurrencyInstrumentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |