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Financial instruments and risk management - Summary of maximum credit risk exposure of the Group's financial assets (Detail) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Trade and other financial receivables [member]    
Disclosure Of Credit Risk Exposure [Line Items]    
Maximum credit risk exposure $ 3,007 $ 2,985
Credit risk [Member]    
Disclosure Of Credit Risk Exposure [Line Items]    
Maximum credit risk exposure 17,156 14,993
Credit risk [Member] | Cash and cash equivalents [member]    
Disclosure Of Credit Risk Exposure [Line Items]    
Maximum credit risk exposure 10,773 10,550
Credit risk [Member] | Derivative assets [member]    
Disclosure Of Credit Risk Exposure [Line Items]    
Maximum credit risk exposure 556 267
Credit risk [Member] | Loans to equity accounted units [member]    
Disclosure Of Credit Risk Exposure [Line Items]    
Maximum credit risk exposure 38 39
Credit risk [Member] | Fair value [member] | Loans And Receivables [Member] | Held to maturity assets [member] | Investments [member]    
Disclosure Of Credit Risk Exposure [Line Items]    
Maximum credit risk exposure $ 2,782 $ 1,152