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Deferred Taxation - Deferred tax liabilities and assets, prior to offsetting of balances (Parenthetical) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Deferred tax liabilities $ 3,628 $ 3,121
Deferred tax assets 3,395 3,728
Deferred tax is not recognised on the unremitted earnings of subsidiaries and joint ventures 3,242 2,523
Tax payable on unremitted earnings $ 131 125
Deferred tax loss recovery period 6 years  
Recognised and unrecognised deferred tax assets $ 7,071 7,170
Unrecognised deferred tax assets 3,676 3,442
Unused tax losses [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Deferred tax assets 1,679 1,309
Later than one year [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Deferred tax liabilities 3,615 3,109
Deferred tax assets $ 3,386 $ 3,721