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Trade and Other Receivables - Schedule of Trade and Other Receivables (Parenthetical) (Detail) - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Australian oil derivative contracts [member]      
Trade and Other Receivables [line items]      
Gold and oil derivative contracts $ 1.0 $ 1.7 $ 5.1
Ghanaian oil derivative contracts [member]      
Trade and Other Receivables [line items]      
Gold and oil derivative contracts 0.1 3.0 9.0
Ghanaian gold derivative contracts [member]      
Trade and Other Receivables [line items]      
Gold and oil derivative contracts 0.0 2.4 0.0
Gold derivative contracts at south deep [member]      
Trade and Other Receivables [line items]      
Gold and oil derivative contracts 0.0 0.0 10.9
Peruvian copper derivative contracts [member]      
Trade and Other Receivables [line items]      
Gold and oil derivative contracts $ 0.0 $ 1.2 $ 0.0