Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Abstract]
Land	$ 241	$ 240
Buildings	737	717
Capital leases	163	165
Equipment and other	2,102	2,042
Property and equipment, gross	3,243	3,164
Less accumulated depreciation and amortization	1,838	1,731
Net property and equipment	1,405	1,433
Depreciation expense, including capitalized lease amortization	240	249	$ 251
Amortization expense related to capital leases	16	17	$ 17
Accumulated amortization of capital leases	$ 91	$ 78