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Goodwill - Summary of goodwill (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Disclosure of reconciliation of changes in goodwill [Line Items]    
Goodwill at beginning of period $ 922 $ 912
Adjustment on currency translation 24 10
Goodwill at end of period 946 922
Cost    
Disclosure of reconciliation of changes in goodwill [Line Items]    
Goodwill at beginning of period 16,926 15,861
Goodwill at end of period 17,341 16,926
Accumulated impairment    
Disclosure of reconciliation of changes in goodwill [Line Items]    
Goodwill at beginning of period (16,004) (14,949)
Goodwill at end of period $ (16,395) $ (16,004)