Restructuring Restructuring Liability (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Reserve [Roll Forward]
Beginning Balance	$ 115	$ 115	$ 37
Restructuring	52	129	167	$ 65
Payments made during the period		(127)	(90)
Foreign currency and other		15	1
Ending Balance		132	115	37
Employee Termination Benefits Liability
Restructuring Reserve [Roll Forward]
Beginning Balance	114	114	37
Restructuring		129	166
Payments made during the period		(127)	(90)
Foreign currency and other		15	1
Ending Balance		131	114	37
Other Exit Costs Liability
Restructuring Reserve [Roll Forward]
Beginning Balance	$ 1	1	0
Restructuring		0	1
Payments made during the period		0	0
Foreign currency and other		0	0
Ending Balance		$ 1	$ 1	$ 0