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Property, plant and equipment - Summary of property, plant and equipment (Parenthetical) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of detailed information about property, plant and equipment [Line Items]      
Depreciation of property, plant and equipment $ 4,198 $ 4,567 $ 4,438
Average borrowing rate used for capitalisation of interest 4.45% 4.20%  
Loans secured by non-current assets collateral $ 4,677 $ 4,783  
Capitalised production phase stripping costs [Member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Capitalised production phase stripping costs, carrying amount 1,815 1,967  
Capitalisation of property, plant and equipment 327    
Capitalisation offset by depreciation 299    
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 1,374 1,511  
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 441 456  
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 194 203 $ 173
Freehold [member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Land and buildings carrying amount 7,294 7,276  
Long leasehold [member]      
Disclosure of detailed information about property, plant and equipment [Line Items]      
Land and buildings carrying amount $ 82 40  
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 $ 3,122 $ 3,378  
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