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Commitments - Additional Information (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Disclosure of Information about Guarantees [Line Items]    
Leases contracted for   $ 33.4
Contractual capital commitments $ 514.7 47.9
Salares Norte [Member]    
Disclosure of Information about Guarantees [Line Items]    
Contractual capital commitments 514.7  
Payments for development project expenditure 454.0  
South African Peruvian Ghanaian And Australian Operations [member]    
Disclosure of Information about Guarantees [Line Items]    
Environmental obligation guarantees amount $ 191.8 $ 154.3