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Operating leases - Summary of Future Minimum Lease Payments Under Non-cancellable Operating Leases (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of maturity analysis of operating lease payments [line items]
Minimum lease payments payable under non-cancellable operating lease	$ 509	$ 534
Due within one year [member]
Disclosure of maturity analysis of operating lease payments [line items]
Minimum lease payments payable under non-cancellable operating lease	56	56
Between 1 and 2 years [member]
Disclosure of maturity analysis of operating lease payments [line items]
Minimum lease payments payable under non-cancellable operating lease	54	46
Between 2 and 3 years [member]
Disclosure of maturity analysis of operating lease payments [line items]
Minimum lease payments payable under non-cancellable operating lease	67	45
Between 3 and 4 years [member]
Disclosure of maturity analysis of operating lease payments [line items]
Minimum lease payments payable under non-cancellable operating lease	35	60
Between 4 and 5 years [member]
Disclosure of maturity analysis of operating lease payments [line items]
Minimum lease payments payable under non-cancellable operating lease	31	30
More than 5 years [member]
Disclosure of maturity analysis of operating lease payments [line items]
Minimum lease payments payable under non-cancellable operating lease	$ 266	$ 297