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Intangible assets - Summary of exploration and evaluation expenditure (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Exploration And Evaluation Expenditure [Abstract]      
Net expenditure in the year (net of proceeds of US$3 million (2016: US$208 million; 2015: US$nil) on disposal of undeveloped projects) $ (493) $ (284) $ (705)
Non-cash movements and non-cash proceeds on disposal of undeveloped projects (24) (177) (15)
Amount capitalised during the year 57 8 152
Net charge for the year (460) (453) (568)
Reconciliation to income statement      
Exploration and evaluation costs (445) (497) (576)
Profit relating to interests in undeveloped projects (15) 44 8
Net charge for the year $ (460) $ (453) $ (568)