Segment Reporting - Revenue and Long-lived Assets by Geography (Details) $ in Millions		12 Months Ended
		Dec. 31, 2017 USD ($) service_offering	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | service_offering		1
Total Revenues		$ 10,265	$ 10,771	$ 11,465
Long-Lived Assets	[1]	1,292	1,361
United States
Segment Reporting Information [Line Items]
Total Revenues		6,064	6,403	6,734
Long-Lived Assets	[1]	770	824
Europe
Segment Reporting Information [Line Items]
Total Revenues		2,697	2,861	3,155
Long-Lived Assets	[1]	355	359
Other areas
Segment Reporting Information [Line Items]
Total Revenues		1,504	1,507	$ 1,576
Long-Lived Assets	[1]	$ 167	$ 178

[1] Long-lived assets are comprised of (i) Land, buildings and equipment, net, (ii) Equipment on operating leases, net, (iii) Internal use software, net and (iv) Product software, net.