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Included in (Loss)/Profit Before Royalties and Taxation - Schedule of Amounts Included in (Loss)/Profit Before Royalties and Taxation (Parenthetical) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Line items represents amounts included in profit before royalties and taxation [line items]      
Restructuring costs $ 113.9 $ 9.2 $ 11.7
South deep [member]      
Line items represents amounts included in profit before royalties and taxation [line items]      
Restructuring costs 11.2 2.3 0.0
Damang [member]      
Line items represents amounts included in profit before royalties and taxation [line items]      
Restructuring costs 13.9 2.2 9.9
Tarkwa [member]      
Line items represents amounts included in profit before royalties and taxation [line items]      
Restructuring costs 88.8 4.7 0.2
Australia [member]      
Line items represents amounts included in profit before royalties and taxation [line items]      
Restructuring costs $ 0.0 $ 0.0 $ 1.6