Leased Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Leases [Abstract]
Gross rental expense	$ 318	$ 324	$ 387
Sublease rental income	(27)	(33)	(40)
Rent expense, net	291	$ 291	$ 347
Future Minimum Payments Due, Fiscal Year Maturity
2017	11
2018	8
2019	6
2020	4
2021	15
2022 and Beyond	26
Total	70
Imputed Interest, Fiscal Year Maturity
2017	(3)
2018	(3)
2019	(3)
2020	(3)
2021	(2)
2022 and Beyond	(15)
Total	(29)
Present Value, Fiscal Year Maturity
2017	8
2018	5
2019	3
2020	1
2021	13
2022 and Beyond	11
Total	41
Future Minimum Payments Due, Fiscal Year Maturity
2017	266
2018	202
2019	154
2020	118
2021	87
2022 and Beyond	267
Total	1,094
Minimum Sublease Rentals, Fiscal Year Maturity
2017	(18)
2018	(11)
2019	(7)
2020	(5)
2021	(3)
2022 and Beyond	(27)
Total	(71)
Future Minimum Payments Due, Net of Sublease Rentals, Fiscal Year Maturity
2017	248
2018	191
2019	147
2020	113
2021	84
2022 and Beyond	240
Total	1,023
Imputed interest	(166)
Present value	$ 857