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Financial instruments related to commodity contracts - Cash flow hedge (Details) - Financial instruments related to commodity contracts - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Cash flow hedge      
Profit (Loss) recorded in equity during the period $ 3 $ 71 $ (69)
Recycled amount from equity to the income statement during the period 3 6 1
Ineffective portion of the cash flow hedges $ 0 $ 0 $ (5)
Cash flow hedge      
Cash flow hedge      
Maximum maturity of most derivatives 1 year