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Cost of Sale - Summary of Cost of Sale (Parenthetical) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of cost of sales [line items]      
Increase in amortisation and depreciation $ 748.1 $ 671.4 [1] $ 591.5 [1]
Increase in amortisation 5.7    
Cerro corona [member]      
Disclosure of cost of sales [line items]      
Increase in amortisation and depreciation 24.5    
Australia [member]      
Disclosure of cost of sales [line items]      
Increase in amortisation and depreciation 298.1 $ 273.6 $ 233.4
Increase in amortisation $ 5.7    
[1] As Restated - Refer note 40 for further details.