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Risk Management Activities - Credit Risk - Narrative (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of Financial Risk Management [line items]        
Cash and cash equivalents $ 524.7 $ 886.8 $ 515.0 $ 219.7
Environmental trust funds 88.1 $ 79.3 $ 69.5  
Loan advanced – contractor        
Disclosure of Financial Risk Management [line items]        
Financial assets 68.4      
Loan advanced – contractor | Lifetime expected credit losses        
Disclosure of Financial Risk Management [line items]        
Financial assets $ 41.1      
Peru        
Disclosure of Financial Risk Management [line items]        
Percentage of cash receipts on revenue recognition 90.00%      
Percentage of cash receipts at the end of quotation period 10.00%      
Counter party exposure        
Disclosure of Financial Risk Management [line items]        
Percentage of maximum investment in financial institutions' equity 2.50%