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Trade and other receivables - Summary of Ageing of Trade and Other Receivables (Detail) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Financial assets at end of period        
Gross $ 387 $ 533    
Credit loss allowance (78) (18) $ (11) $ (77)
Net 309 515    
Not past due [member]        
Financial assets at end of period        
Gross 153 363    
Credit loss allowance (1) (3)    
Net 152 360    
Past due 1 to 30 days [member]        
Financial assets at end of period        
Gross 59 74    
Credit loss allowance (2) (3)    
Net 57 71    
Past due 31 to 90 days [member]        
Financial assets at end of period        
Gross 61 56    
Credit loss allowance (6) (5)    
Net 55 51    
Past due more than 90 days [member]        
Financial assets at end of period        
Gross 40 35    
Credit loss allowance (7) (7)    
Net 33 28    
Past due more than 180 days [member]        
Financial assets at end of period        
Gross 74 5    
Credit loss allowance (62)      
Net $ 12 $ 5