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Risk Management Activities - Summary of gain loss from derivative financial instruments (Detail) - Market risk [member] - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of maturity analysis for non-derivative financial liabilities [line items]      
Gain (loss) on hedge ineffectiveness recognised in profit or loss $ (238.0) $ 21.0 $ 34.4
South Deep gold hedge [member]      
Disclosure of maturity analysis for non-derivative financial liabilities [line items]      
Gain (loss) on hedge ineffectiveness recognised in profit or loss (25.8) (3.2) 10.9
Ghana gold hedge [member]      
Disclosure of maturity analysis for non-derivative financial liabilities [line items]      
Gain (loss) on hedge ineffectiveness recognised in profit or loss (37.7) 22.0  
Ghana oil hedge [member]      
Disclosure of maturity analysis for non-derivative financial liabilities [line items]      
Gain (loss) on hedge ineffectiveness recognised in profit or loss 2.5 1.5 8.8
Peru copper hedge [member]      
Disclosure of maturity analysis for non-derivative financial liabilities [line items]      
Gain (loss) on hedge ineffectiveness recognised in profit or loss   9.2 (5.7)
Australia gold hedge [member]      
Disclosure of maturity analysis for non-derivative financial liabilities [line items]      
Gain (loss) on hedge ineffectiveness recognised in profit or loss (178.8) (4.6) 15.3
Australia oil hedge [member]      
Disclosure of maturity analysis for non-derivative financial liabilities [line items]      
Gain (loss) on hedge ineffectiveness recognised in profit or loss 2.3 1.4 $ 5.1
Australia foreign currency hedge [member]      
Disclosure of maturity analysis for non-derivative financial liabilities [line items]      
Gain (loss) on hedge ineffectiveness recognised in profit or loss (7.2) (9.1)  
Maverix warrants – gain on fair value [member]      
Disclosure of maturity analysis for non-derivative financial liabilities [line items]      
Gain (loss) on hedge ineffectiveness recognised in profit or loss 4.2 $ 3.8  
Gain on fair value on disposal of Maverix [member]      
Disclosure of maturity analysis for non-derivative financial liabilities [line items]      
Gain (loss) on hedge ineffectiveness recognised in profit or loss $ 2.5