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Royalties - Summary of Royalties (Parenthetical) (Detail)
 12 Months Ended
Dec. 31, 2020
USD ($)
Times
Dec. 31, 2019
Dec. 31, 2018
Range One [member] | Bottom of range [member]      
Disclosure of information about royalty arrangements [line items]      
Average gold price $ 0.00    
Range One [member] | Top of range [member]      
Disclosure of information about royalty arrangements [line items]      
Average gold price 1,299.99    
Range Two [member] | Bottom of range [member]      
Disclosure of information about royalty arrangements [line items]      
Average gold price 1,300.00    
Range Two [member] | Top of range [member]      
Disclosure of information about royalty arrangements [line items]      
Average gold price 1,449.99    
Range Three [member] | Bottom of range [member]      
Disclosure of information about royalty arrangements [line items]      
Average gold price 1,450.00    
Range Three [member] | Top of range [member]      
Disclosure of information about royalty arrangements [line items]      
Average gold price 2,299.99    
Range Four [member] | Bottom of range [member]      
Disclosure of information about royalty arrangements [line items]      
Average gold price $ 2,300.00    
South Africa [member]      
Disclosure of information about royalty arrangements [line items]      
Royalty in refined minerals, description The Mineral and Petroleum Resource Royalty Act 2008 (“Royalty Act”) was promulgated on 24 November 2008 and became effective from 1 March 2010. The Royalty Act imposes a royalty on refined (mineral resources that have undergone a comprehensive level of beneficiation such as smelting and refining as defined in Schedule 1 of the Act) and unrefined (mineral resources that have undergone limited beneficiation as defined in Schedule 2 of the Act) minerals payable to the state. The royalty in respect of refined minerals (which include gold refined to 99.5% and above and platinum) is calculated by dividing earnings before interest and taxes (“EBIT”) by the product of 12.5 times gross revenue calculated as a percentage, plus an additional 0.5%. EBIT refers to taxable mining income (with certain exceptions such as no deduction for interest payable and foreign exchange losses) before assessed losses but after capital expenditure. A maximum royalty of 5% has been introduced on refined minerals. The effective rate of royalty tax payable for the year ended 31 December 2020 was 0.5% of mining revenue (2019: 0.5% and 2018: 0.5%) equalling the minimum charge per the formula.    
Royalty effective rate 0.50% 0.50% 0.50%
Australia [member]      
Disclosure of information about royalty arrangements [line items]      
Royalty effective rate 2.50% 2.50% 2.50%
Peru [member]      
Disclosure of information about royalty arrangements [line items]      
Royalty effective rate 3.90% 3.60% 4.00%
Peru [member] | Bottom of range [member]      
Disclosure of information about royalty arrangements [line items]      
Royalty rate 1.00%    
Peru [member] | Top of range [member]      
Disclosure of information about royalty arrangements [line items]      
Royalty rate 12.00%    
Gold refined minerals [member] | South Africa [member]      
Disclosure of information about royalty arrangements [line items]      
Gold refining percentage 99.50%    
Refined minerals [member] | South Africa [member]      
Disclosure of information about royalty arrangements [line items]      
Number of times gross revenue | Times 12.5    
Additional percentage 0.50%    
Refined minerals [member] | South Africa [member] | Top of range [member]      
Disclosure of information about royalty arrangements [line items]      
Royalty rate 5.00%    
Gold royalty [member] | Range One [member]      
Disclosure of information about royalty arrangements [line items]      
Royalty rate 3.00%    
Gold royalty [member] | Range Two [member]      
Disclosure of information about royalty arrangements [line items]      
Royalty rate 3.50%    
Gold royalty [member] | Range Three [member]      
Disclosure of information about royalty arrangements [line items]      
Royalty rate 4.10%    
Gold royalty [member] | Range Four [member]      
Disclosure of information about royalty arrangements [line items]      
Royalty rate 5.00%    
Gold royalty [member] | Australia [member]      
Disclosure of information about royalty arrangements [line items]      
Royalty rate 2.50% 2.50% 2.50%