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Provisions, including post-retirement benefits - Summary of Provisions, including post-retirement benefits (Parenthetical) (Detail) - USD ($)
$ in Millions
 1 Months Ended 12 Months Ended
Sep. 30, 2020
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of other provisions [Line Items]        
Non-current provisions   $ 15,936.0 $ 13,704.0  
Remaining lives of operations and infrastructure   one to over 50 years    
Remaining lives of operations and infrastructure present closure obligation   17 years 18 years  
Provisions   $ 17,665.0 $ 15,103.0 $ 13,608.0
Risk free interest rate on provisions 1.50% 1.50% 2.00%  
Bottom of range        
Disclosure of other provisions [Line Items]        
Provisions   $ 2,600.0    
Risk free interest rate on provisions   1.00%    
Top of range        
Disclosure of other provisions [Line Items]        
Provisions   $ 1,300.0    
Risk free interest rate on provisions   3.00%    
Other employee entitlements        
Disclosure of other provisions [Line Items]        
Provision for long service leave   $ 283.0 $ 248.0  
Provision for redundancy and severance payments   62.0 30.0  
Non-current provisions   92.0    
Provisions   419.0 354.0  
Close down and restoration/ environmental        
Disclosure of other provisions [Line Items]        
Non-current provisions   12,558.0    
Provisions   13,335.0 11,090.0  
Close down and restoration/ environmental | Diavik Diamond Mines (2012) Inc.        
Disclosure of other provisions [Line Items]        
Provisions relating to insurance recoveries and other financial assets held   574.0 166.0  
Close down and restoration/ environmental | Between 1 and 5 years        
Disclosure of other provisions [Line Items]        
Non-current provisions   468.0 382.0  
Close down and restoration/ environmental | More than 5 years        
Disclosure of other provisions [Line Items]        
Non-current provisions   937.0 $ 883.0  
Close down and restoration/ environmental | Bottom of range        
Disclosure of other provisions [Line Items]        
Provision capitalised to property, plant and equipment   2,400.0    
Provision charged to the income statement   200.0    
Close down and restoration/ environmental | Top of range        
Disclosure of other provisions [Line Items]        
Provision capitalised to property, plant and equipment   1,200.0    
Provision charged to the income statement   $ 100.0