Restructuring Actions and Exit Activities - Roll Forward (Details) - Employee-Related - 2017 Restructuring Actions - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Restructuring Reserve Roll Forward
Restructuring actions balances, Beginning Balance	$ 88
Expenses incurred		$ 99
Cash payments	(5)	(8)
Adjustments	(4)	(3)
Restructuring actions balances, Ending Balance	$ 79	$ 88