XML 688 R208.htm IDEA: XBRL DOCUMENT v3.20.4
Principal joint ventures - Summary of joint ventures (Detail) - shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of joint ventures [line items]      
Number of shares held (in shares) 0 0 0
Minera Escondida Limitada      
Disclosure of joint ventures [line items]      
Group interest (%) 30.00%    
Sohar      
Disclosure of joint ventures [line items]      
Group interest (%) 20.00%    
Sohar | Ordinary      
Disclosure of joint ventures [line items]      
Number of shares held (in shares) 37,500    
Proportion of class held (%) 20.00%    
Group interest (%) 20.00%