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Principal accounting policies - Additional information (Detail)
$ in Millions, $ in Billions
 1 Months Ended 12 Months Ended
Sep. 30, 2020
Dec. 31, 2020
USD ($)
Operation
Dec. 31, 2019
USD ($)
Dec. 31, 2020
AUD ($)
Dec. 31, 2018
USD ($)
Disclosure of initial application of standards or interpretations [Line Items]          
Credit derivative, nominal amount   $ 7,300      
Materiality threshold   550 $ 350    
Trade payables   $ 3,125 2,855    
Number of operations | Operation   10      
Increase in closure and environmental liabilities   $ 74 444    
Operations in closure, monitoring and remediation, cost estimation period   30 years      
Decreasing provision   $ 1,200      
Provisions   $ 17,665 $ 15,103   $ 13,608
Risk free rate decrease 0.50%        
Risk free interest rate on provisions 1.50% 1.50% 2.00%    
Onerous contracts provision   $ 219 $ 284    
Intragroup loans       $ 14  
Non-cancellable operating lease commitments not expected to be charged against EBITDA   $ 2,000      
Oyu Tolgoi          
Disclosure of initial application of standards or interpretations [Line Items]          
Proportion of indirect ownership interest in subsidiary   33.50%      
Turquoise Hill Resources Ltd(including Oyu Tolgoi LLC)          
Disclosure of initial application of standards or interpretations [Line Items]          
Group interest (%)   50.80%      
Erdenes Oyu Tolgoi LLC | Floating interest rate          
Disclosure of initial application of standards or interpretations [Line Items]          
Borrowings, interest rate basis   6.50%   6.50%  
Close down and restoration/ environmental          
Disclosure of initial application of standards or interpretations [Line Items]          
Provisions   $ 13,335 11,090    
Trade Payables Subject To Early Settlement Election          
Disclosure of initial application of standards or interpretations [Line Items]          
Trade payables   $ 551 573    
Escondida Joint Venture          
Disclosure of initial application of standards or interpretations [Line Items]          
Decrease in investment in Escondida Joint Venture     $ 138    
Rio Tinto Kennecott          
Disclosure of initial application of standards or interpretations [Line Items]          
Operations with remaining lives   10 years      
Environmental loss contingencies, gross   $ 600