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Stated Capital - Schedule of Stated Capital (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Jan. 01, 2018
May 25, 2017
May 24, 2017
Disclosure of classes of share capital [line items]          
Stated capital $ 3,622.5 $ 3,622.5 [1] $ 3,622.5    
Stated capital 3,622.5 $ 3,622.5 [1] $ 3,622.5    
Exercise of employee share options   0      
Authorised         1,000,000,000
Ordinary Shares [member]          
Disclosure of classes of share capital [line items]          
Stated capital 3,622.5 $ 3,622.5      
Stated capital $ 3,622.5 $ 3,622.5      
In issue at 1 January 821,532,707 821,532,707      
Exercise of employee share options 7,100,000        
In issue at 31 December 828,632,707 821,532,707      
Authorised 2,000,000,000 2,000,000,000   1,000,000,000 1,000,000,000
[1] Refer note 42.