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Property, plant and equipment - Summary of property, plant and equipment (Footnotes) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of detailed information about property, plant and equipment [Line Items]      
Depreciation of property, plant and equipment $ (3,796) $ (3,979)  
Average borrowing rate used for capitalisation of interest 4.20% 5.30%  
Loans secured by non-current assets collateral $ 4,518 $ 4,540  
Capitalised production phase stripping costs      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Capitalised production phase stripping costs, carrying amount 2,398 2,276  
Capitalisation of property, plant and equipment 380    
Capitalisation offset by depreciation (267)    
Capitalised production phase stripping costs | Property, plant and equipment      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Capitalised production phase stripping costs, carrying amount 2,019 1,833  
Capitalised production phase stripping costs | Investment in equity accounted units      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Capitalised production phase stripping costs, carrying amount 379 443  
Capitalised production phase stripping costs | Subsidiaries      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Depreciation of property, plant and equipment $ (145) (139) $ (134)
Buildings | Bottom of range      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment 5 years    
Buildings | Top of range      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment 50 years    
Plant and equipment      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Depreciation of property, plant and equipment $ (2,776) $ (2,869)  
Plant and equipment | Bottom of range      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment 3 years    
Plant and equipment | Top of range      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment 50 years    
Power generating assets | Bottom of range      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment 25 years    
Power generating assets | Top of range      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment 50 years