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Property, plant and equipment - Summary of property, plant and equipment (Parenthetical) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of detailed information about property, plant and equipment [Line Items]      
Depreciation of property, plant and equipment $ 3,882 $ 4,198 $ 4,567
Average borrowing rate used for capitalisation of interest 4.90% 4.45%  
Loans secured by non-current assets collateral $ 4,562 $ 4,677  
Capitalised production phase stripping costs [Member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Capitalised production phase stripping costs, carrying amount 2,050 1,815  
Capitalisation of property, plant and equipment 526    
Capitalisation offset by depreciation 274    
Capitalised production phase stripping costs [Member] | Property, plant and equipment [member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Capitalised production phase stripping costs, carrying amount 1,572 1,374  
Capitalised production phase stripping costs [Member] | Investment in equity accounted units [member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Capitalised production phase stripping costs, carrying amount 478 441  
Capitalised production phase stripping costs [Member] | Subsidiaries [Member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Depreciation of property, plant and equipment 134 194 $ 203
Freehold [member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Land and buildings carrying amount 6,240 7,294  
Long leasehold [member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Land and buildings carrying amount $ 23 82  
Land [Member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment Not depreciated    
Buildings [Member] | 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 [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    
Plant and equipment [member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Depreciation of property, plant and equipment $ 2,836 $ 3,122  
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 P50Y    
Power generating assets [Member] | Bottom of range [Member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment P25Y    
Power generating assets [Member] | Top of range [Member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment P50Y    
Capital works in progress [member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Useful lives of property, plant and equipment Not depreciated