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New Standards and Interpretations Adopted in the Current Year - Additional information (Detail) - USD ($)
$ in Millions
Jan. 01, 2019
Dec. 31, 2019
Dec. 31, 2018
Disclosure of initial application of standards or interpretations [Line Items]      
Right of use assets – leased $ 1,022 $ 1,065 $ 0
Net assets/(liabilities)   45,242 49,823
Retained earnings   $ 23,387 27,025
I F R S16 [Member]      
Disclosure of initial application of standards or interpretations [Line Items]      
Lease liabilities 1,292   1,717
IFRIC 23 [Member]      
Disclosure of initial application of standards or interpretations [Line Items]      
Provision for income tax 44    
Lease liabilities [member]      
Disclosure of initial application of standards or interpretations [Line Items]      
Lease liabilities 1,248    
Lease liabilities [member] | I F R S16 [Member]      
Disclosure of initial application of standards or interpretations [Line Items]      
Right of use assets – leased $ 1,067    
Net assets/(liabilities)     110
Retained earnings     $ 69
Weighted average lessee's incremental borrowing rate applied to lease liabilities recognised at date of initial application of IFRS 16 4.70%