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Goodwill - Summary of goodwill (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure of reconciliation of changes in goodwill [Line Items]    
Goodwill at beginning of period $ 1,037 $ 951
Adjustment on currency translation (125) 86
Goodwill at end of period 912 1,037
Cost [member]    
Disclosure of reconciliation of changes in goodwill [Line Items]    
Goodwill at beginning of period 17,942 17,144
Goodwill at end of period 15,861 17,942
Accumulated impairment [Member]    
Disclosure of reconciliation of changes in goodwill [Line Items]    
Goodwill at beginning of period (16,905) (16,193)
Goodwill at end of period $ (14,949) $ (16,905)