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Inventories (Details) - USD ($)
$ in Millions
Mar. 31, 2018
Dec. 31, 2017
Inventories    
Raw materials $ 68 $ 66
Materials and supplies 470 447
Finished goods 562 776
Inventories, Gross 1,100 1,289
Revaluation to LIFO (43) (43)
Total $ 1,057 $ 1,246