Restructuring Charges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Current Fiscal Year End Date	--12-31
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	$ 87	$ 51
Charge to Earnings	275	173	$ 201
Cash Paid	(172)	(119)
Non-cash and Other	(28)	(18)
Revision of Estimate	0	0
Restructuring reserve, ending balance	162	87	51
Employee termination costs
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	71	30
Charge to Earnings	185	133
Cash Paid	(125)	(90)
Non-cash and Other	0	(2)
Revision of Estimate	0	0
Restructuring reserve, ending balance	131	71	30
Asset impairment costs
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	0	0
Charge to Earnings	40	17
Cash Paid	0	(1)
Non-cash and Other	(40)	(16)
Revision of Estimate	0	0
Restructuring reserve, ending balance	0	0	0
Facility exit costs
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	2	3
Charge to Earnings	28	15
Cash Paid	(28)	(16)
Non-cash and Other	0	0
Revision of Estimate	0	0
Restructuring reserve, ending balance	2	2	3
Other exit costs
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	14	18
Charge to Earnings	22	8
Cash Paid	(19)	(12)
Non-cash and Other	12	0
Revision of Estimate	0	0
Restructuring reserve, ending balance	$ 29	$ 14	$ 18