Asset Impairment, Exit and Implementation Costs (Restructuring Liabilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Restructuring Reserve [Roll Forward]
Balance at beginning of period	$ 33	$ 79
Charges	154	25
Cash spent	(32)	(71)
Balance at end of period	$ 155	$ 33