XML 347 R144.htm IDEA: XBRL DOCUMENT v3.10.0.1
Intangible assets - Summary of exploration and evaluation expenditure (Parenthetical) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of detailed information about intangible assets [Line Items]      
Net proceeds on disposal of undeveloped projects $ 233 $ 3 $ 208
Valeria [Member]      
Disclosure of detailed information about intangible assets [Line Items]      
Gain on sales of undeveloped properties 83    
Winchester South [Member]      
Disclosure of detailed information about intangible assets [Line Items]      
Gain on sales of undeveloped properties $ 195