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Property, plant and equipment - Summary of property, plant and equipment (Footnotes) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of detailed information about property, plant and equipment [Line Items]      
Depreciation of property, plant and equipment $ (3,979) $ (3,882)  
Average borrowing rate used for capitalisation of interest 5.30% 4.90%  
Loans secured by non-current assets collateral $ 4,540 $ 4,562  
Capitalised production phase stripping costs      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Capitalised production phase stripping costs, carrying amount 2,276 2,050  
Capitalisation of property, plant and equipment 536    
Capitalisation offset by depreciation (316)    
Capitalised production phase stripping costs | Property, plant and equipment [Member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Capitalised production phase stripping costs, carrying amount 1,833 1,572  
Capitalised production phase stripping costs | Investment in equity accounted units [Member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Capitalised production phase stripping costs, carrying amount 443 478  
Capitalised production phase stripping costs | Subsidiaries [Member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Depreciation of property, plant and equipment (139) (134) $ (194)
Freehold      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Land and buildings carrying amount 6,377 6,240  
Long leasehold      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Land and buildings carrying amount $ 26 23  
Buildings | Bottom of range [member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment 5 years    
Buildings | Top of range [member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment 50 years    
Plant and equipment [Member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Depreciation of property, plant and equipment $ (2,869) $ (2,836)  
Plant and equipment [Member] | Bottom of range [member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment 3 years    
Plant and equipment [Member] | Top of range [member]      
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 [member]      
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 [member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment 50 years    
Capital works in progress [Member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Depreciation of property, plant and equipment $ 0