Leased Assets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Leased Assets [Line Items]
Gross rental expense	$ 387	$ 400	$ 417
Sublease rental income	(40)	(43)	(53)
Rent expense, net	347	357	364
Capital leases, minimum lease payments, Next Twelve months	14
Capital leases, minimum lease payments, Due in Two Years	12
Capital leases, minimum lease payments, Due in Three Years	10
Capital leases, minimum lease payments, Due in Four Years	8
Capital leases, minimum lease payments, Due in Five Years	5
Capital leases, minimum lease payments, Due Thereafter	48
Capital leases, minimum lease payments	97
Capital leases, imputed interest, Next Twelve Months	(4)
Capital leases, imputed interest, Due in Two Years	(4)
Capital leases, imputed interest, Due in Three Years	(3)
Capital leases, imputed interest, Due in Four Years	(3)
Capital leases, imputed interest, Due in Five Years	(3)
Capital leases, imputed interest, Due Thereafter	(21)
Capital leases, imputed interest	(38)
Capital leases. present value, Next Twelve Months	10
Capital leases. present value, Due in Two Years	8
Capital leases. present value, Due in Three Years	7
Capital leases. present value, Due in Four Years	5
Capital leases. present value, Due in Five Years	2
Capital leases. present value, Due Thereafter	27
Capital leases. present value	59
Operating leases, minimum lease payments, Next Twelve Months	307
Operating leases, minimum lease payments, Due in Two Years	233
Operating leases, minimum lease payments, Due in Three Years	178
Operating leases, minimum lease payments, Due in Four Years	128
Operating leases, minimum lease payments, Due in Five Years	98
Operating leases, minimum lease payments, Due Thereafter	322
Operating leases, minimum lease payments	1,266
Operating leases, minimum sublease rentals, Next Twelve Months	(32)
Operating leases, minimum sublease rentals, in Two Years	(24)
Operating leases, minimum sublease rentals, in Three Years	(14)
Operating leases, minimum sublease rentals, in Four Years	(7)
Operating leases, minimum sublease rentals, in Five Years	(3)
Operating leases, minimum sublease rentals, Thereafter	(9)
Operating leases, minimum sublease rentals	(89)
Operating leases, Next Twelve Months	275
Operating leases, Due in Two Years	209
Operating leases, Due in Three Years	164
Operating leases, Due in Four Years	121
Operating leases, Due in Five Years	95
Operating leases, Due Thereafter	313
Operating leases	1,177
Operating leases, imputed interest	(227)
Operating leases, present value	$ 950