Land, Buildings, Equipment and Software, Net - Internal Use Software (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Land, Buildings, Equipment and Software [Abstract]
Additions to internal use software	$ 36	$ 45	$ 64
Internal use software, capitalized costs, net	$ 209	$ 218
Internal Use and Product Software, Useful Lives Minimum	3 years
Internal Use and Product Software, Useful Lives Maximum	7 years