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Cash and cash equivalents - Additional information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure of cash and cash equivalents [Line Items]    
Restricted cash and cash equivalents $ 186 $ 290
Repayment of third party borrowings 142 158
Subsidiaries [Member]    
Disclosure of cash and cash equivalents [Line Items]    
Restricted cash and cash equivalents 1,090 1,089
Repayment of third party borrowings $ 864 $ 703