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Impairment, Net of Reversal of Impairment of Investments and Assets - Summary of Impairment, Net of Reversal of Impairment of Investments and Assets (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Disclosures of impairment of investments and assets [line items]      
Investments $ (30.8) $ 62.3 $ (9.6)
Property, plant and equipment (11.6) (11.7) (0.2)
Impairment, net of reversal of impairment of investments and assets $ (42.4) 50.6 (9.8)
Lepanto Consolidated Mining Company      
Disclosures of impairment of investments and assets [line items]      
Interest in subsidiary 60.00%    
Other      
Disclosures of impairment of investments and assets [line items]      
Property, plant and equipment $ (11.6) (11.7) (0.2)
Capitalised exploration costs      
Disclosures of impairment of investments and assets [line items]      
Property, plant and equipment (10.0) 0.0 0.0
Drilling costs | Damang      
Disclosures of impairment of investments and assets [line items]      
Property, plant and equipment 0.0 (9.8) 0.0
Redundant assets in Peru      
Disclosures of impairment of investments and assets [line items]      
Property, plant and equipment (1.6) (1.9) (0.2)
Far Southeast Gold Resources Incorporated (FSE)      
Disclosures of impairment of investments and assets [line items]      
Investments $ (30.8) $ 62.3 $ (9.6)
Far Southeast Gold Resources Incorporated (FSE) | Lepanto Consolidated Mining Company      
Disclosures of impairment of investments and assets [line items]      
Interest in subsidiary 60.00%