Land, Buildings, Equipment and Software, Net - Depreciation Expense, Operating Lease Rent Expense, Minimum Operating Lease Commitments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Land, Buildings, Equipment and Software, Net [Abstract]
Depreciation expense	$ 136	$ 148	$ 151
Operating lease expense	161	157	$ 164
Capital Leased Assets, Gross	35	$ 31
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2018	127
2019	100
2020	77
2021	55
2022	42
Thereafter	$ 48