Investments in joint ventures - Transactions between group and its joint ventures (Details) - Joint ventures - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Sales to joint ventures
Sales to related parties	$ 4,603	$ 3,578	$ 3,327
Related party receivable	251	352	291
Purchases from joint ventures
Purchases of goods, related party	1,336	1,257	943
Related party payables	$ 300	$ 176	$ 120

Purchases from joint ventures [Abstract]

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Sales To Joint Ventures [Abstract]

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The amounts payable resulting from related party transactions. [Refer: Related parties [member]]

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The amounts receivable resulting from related party transactions. [Refer: Related parties [member]]

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The amount of goods purchased by the entity in related party transactions. [Refer: Related parties [member]]

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The amount of revenue arising from the sale of goods in related party transactions. [Refer: Revenue; Related parties [member]]

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