Schedule II - Valuation Accounts and Reserves - Valuation Accounts and Reserves (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts [Member]
Balance at beginning of period	$ 59	$ 48	$ 47
Additions	1	11	1
Balance at end of period	60	59	48
Valuation Allowance of Deferred Tax Assets [Member]
Balance at beginning of period	270	238	298
Additions	241	55	30
Net deductions and other	55	23	90
Balance at end of period	456	270	238
Accumulated Amortization of Purchased Intangible Assets [Member]
Balance at beginning of period	325	265	216
Additions	75	64	49
Net deductions and other	3	4
Balance at end of period	397	325	265
Business Restructuring Reserves [Member]
Balance at beginning of period	5	3	44
Additions		15
Net deductions and other	$ 5	13	41
Balance at end of period		$ 5	$ 3