Inventory Disclosure - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Inventory, Net [Abstract]
Inventories valued on the LIFO basis	$ 341	$ 269
Excess of current replacement cost over LIFO cost of inventories	124	$ 104
Effect of LIFO Inventory Liquidation on Income	$ 1