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Investments in equity accounted units - Additional information (Detail) - USD ($)
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of Investments in equity accounted units [Line Items]      
Investments in equity accounted units with shares listed on recognised stock exchanges $ 0 $ 0  
Net debt of the group (3,651,000,000) 255,000,000 $ (3,845,000,000)
Investment in equity accounted units [Member]      
Disclosure of Investments in equity accounted units [Line Items]      
Net debt of the group $ (1,248,000,000) $ (1,158,000,000)