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Goodwill - Summary of goodwill (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Disclosure of reconciliation of changes in goodwill [Line Items]    
Goodwill at beginning of period $ 951 $ 892
Adjustment on currency translation 86 59
Goodwill at end of period 1,037 951
Cost [member]    
Disclosure of reconciliation of changes in goodwill [Line Items]    
Goodwill at beginning of period 17,144 17,120
Goodwill at end of period 17,942 17,144
Accumulated impairment [Member]    
Disclosure of reconciliation of changes in goodwill [Line Items]    
Goodwill at beginning of period (16,193) (16,228)
Goodwill at end of period $ (16,905) $ (16,193)