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Risk Management Activities - Schedule of Combined Maximum Credit Risk Exposure (Detail) - USD ($)
$ in Millions
Dec. 31, 2021
Dec. 31, 2020
Trade and other receivables    
Disclosure of credit risk exposure [line items]    
VAT, import duties, prepayments, payroll receivables, derivative contracts and diesel rebates $ 181.4 $ 186.9
Environmental trust funds | Credit risk    
Disclosure of credit risk exposure [line items]    
Maximum exposure to credit risk 88.1 79.3
Trade and other receivables | Credit risk    
Disclosure of credit risk exposure [line items]    
Maximum exposure to credit risk 82.3 53.2
Loan advanced – contractor | Credit risk    
Disclosure of credit risk exposure [line items]    
Maximum exposure to credit risk 27.3 68.4
Derivative financial assets | Credit risk    
Disclosure of credit risk exposure [line items]    
Maximum exposure to credit risk 5.1 113.3
Cash and cash equivalents | Credit risk    
Disclosure of credit risk exposure [line items]    
Maximum exposure to credit risk $ 524.7 $ 886.8