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Summary Of Significant Accounting Policies (Schedule Of Inventories) (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
LIFO inventories    
FIFO value $ 1,056 $ 1,390
LIFO valuation reserve (73) (75)
LIFO inventories carrying value 983 1,315
FIFO inventories 2,906 2,705
Market inventories 4,886 4,424
Supplies and other inventories 398 387
Total inventories $ 9,173 $ 8,831