XML 441 R163.htm IDEA: XBRL DOCUMENT v3.19.1
Trade and Other Receivables - Schedule of Trade and Other Receivables (Parenthetical) (Detail) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Australian oil derivative contracts [member]    
Trade and Other Receivables [line items]    
Gold and oil derivative contracts $ 1.7 $ 5.1
Ghanaian oil derivative contracts [member]    
Trade and Other Receivables [line items]    
Gold and oil derivative contracts 3.0 9.0
Ghanaian gold derivative contracts [member]    
Trade and Other Receivables [line items]    
Gold and oil derivative contracts 2.4 0.0
Gold derivative contracts at south deep [member]    
Trade and Other Receivables [line items]    
Gold and oil derivative contracts 0.0 10.9
Peruvian copper derivative contracts [member]    
Trade and Other Receivables [line items]    
Gold and oil derivative contracts $ 1.2 $ 0.0