XML 384 R170.htm IDEA: XBRL DOCUMENT v3.20.1
Provisions - Silicosis Settlement Costs - Additional Information (Detail)
R in Millions, $ in Millions
Dec. 31, 2019
USD ($)
Dec. 31, 2019
ZAR (R)
Dec. 31, 2018
USD ($)
Dec. 31, 2018
ZAR (R)
Disclosure of Provisions [line items]        
Provisions $ 21.2   $ 25.1  
Silicosis [Member]        
Disclosure of Provisions [line items]        
Provisions 21.2 R 297.1 $ 25.1 R 367.8
Nominal amount of provision $ 29.2 R 408.4    
Silicosis [Member] | Government bonds [member]        
Disclosure of Provisions [line items]        
Discount rate on government bonds 10.08% 10.08% 8.74% 8.74%