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Notes to financial information by business unit (Detail) - USD ($)
$ in Millions
 1 Months Ended 6 Months Ended 12 Months Ended
Jul. 16, 2019
Feb. 29, 2020
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2019
Disclosure of operating segments [line items]          
Consolidated sales revenue     $ 19,362 $ 20,722  
EBITDA     5,929 5,484  
Net earnings     3,316 4,130  
Operating assets     $ 44,050   $ 44,183
Percentage of capital expenditure in subsidiaries     100.00%    
Restatement Adjustment For Legacy Alumina Contracts          
Disclosure of operating segments [line items]          
EBITDA       155  
Net earnings       122  
Reportable segments          
Disclosure of operating segments [line items]          
Operating assets     $ 46,198   46,632
Reportable segments | Aluminium, Alumina and Bauxite          
Disclosure of operating segments [line items]          
Consolidated sales revenue     4,487 5,100  
EBITDA     925 1,127  
Net earnings     193 315  
Operating assets     14,370   16,030
Bauxite | Restatement Adjustment For Internal Shipping          
Disclosure of operating segments [line items]          
Consolidated sales revenue       15  
EBITDA       31  
Net earnings       21  
Alumina | Restatement Adjustment For Internal Shipping          
Disclosure of operating segments [line items]          
Consolidated sales revenue       30  
EBITDA       64  
Net earnings       44  
Intra-segment and other | Reportable segments | Aluminium, Alumina and Bauxite          
Disclosure of operating segments [line items]          
Consolidated sales revenue     (1,262) (1,686)  
EBITDA     33 27  
Net earnings     24 20  
Operating assets     817   $ 780
Intra-segment and other | Bauxite And Alumina | Reportable segments | Aluminium, Alumina and Bauxite          
Disclosure of operating segments [line items]          
Consolidated sales revenue     (364) (425)  
EBITDA     4 (2)  
Net earnings     3 (1)  
Operating assets     $ (24) 21  
Hope Downs Joint Venture          
Disclosure of operating segments [line items]          
Proportion of ownership interest in joint venture (as a percent)     50.00%    
Robe river iron associates          
Disclosure of operating segments [line items]          
Proportion of ownership interest in joint venture (as a percent)     65.00%    
Proportion of net beneficial interest     53.00%    
Robe river iron associates | Thirty Percent          
Disclosure of operating segments [line items]          
Net beneficial interest held percentage     30.00%    
Net beneficial interest held percentage as owned subsidiary     60.00%    
Robe river iron associates | Thirty Five Percentage          
Disclosure of operating segments [line items]          
Net beneficial interest held percentage     35.00%    
Net beneficial interest held percentage as owned subsidiary     100.00%    
Diavik          
Disclosure of operating segments [line items]          
Proportion of ownership interest in joint venture (as a percent)     60.00%    
Hamersley          
Disclosure of operating segments [line items]          
Proportion of ownership interest in subsidiary     100.00%    
Oyu Tolgoi | Turquoise Hill Resources Ltd          
Disclosure of operating segments [line items]          
Percentage of share class held in subsidiaries     50.80%    
Oyu Tolgoi | Turquoise Hill Resources Ltd | Oyo Tolgoi Copper-Gold Mine          
Disclosure of operating segments [line items]          
Percentage of share class held in subsidiaries     66.00%    
Argyle          
Disclosure of operating segments [line items]          
Proportion of ownership interest in subsidiary     100.00%    
Rio Tinto Fer Et Titane Inc          
Disclosure of operating segments [line items]          
Proportion of ownership interest in subsidiary     100.00%    
Qit Madagascar Minerals          
Disclosure of operating segments [line items]          
Proportion of ownership interest in subsidiary     80.00%    
Richards Bay Minerals          
Disclosure of operating segments [line items]          
Proportion of ownership interest in subsidiary     74.00%    
Rossing Uranium Limited          
Disclosure of operating segments [line items]          
Proportion of ownership interest in subsidiary 68.60%        
Energy Resources of Australia Limited          
Disclosure of operating segments [line items]          
Proportion of ownership interest in subsidiary   86.30%     68.40%
Consolidated sales revenue     $ 108 118  
Net earnings     $ 21 $ 25  
Simfer Jersey Limited          
Disclosure of operating segments [line items]          
Proportion of ownership interest in subsidiary     53.00%    
Simfer Sa          
Disclosure of operating segments [line items]          
Proportion of ownership interest in subsidiary     85.00%    
Proportion of ownership interests held by non-controlling interests     45.05%    
Gove Alumina Refinery And Rio Tinto Marine          
Disclosure of operating segments [line items]          
Proportion of ownership interest in subsidiary     100.00%