Asset Impairment, Exit and Implementation Costs (Restructuring Liabilities) (Details) - USD ($) $ in Millions	12 Months Ended		24 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017
Restructuring Reserve [Roll Forward]
Balance at beginning of period	$ 79	$ 0	$ 0
Charges	25	152
Cash spent	(71)	(73)
Balance at end of period	$ 33	$ 79	$ 33