Leases - Schedule of Future Lease Payments (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Operating Leases
Remaining 2019	$ 261
2020	223
2021	176
2022	134
2023	90
Thereafter	244
Total future undiscounted lease payments	1,128
Less imputed interest	(62)
Total reported lease liability	1,066
Finance Leases
Remaining 2019	22
2020	21
2021	17
2022	13
2023	7
Thereafter	66
Total future undiscounted lease payments	146
Less imputed interest	(30)
Total reported lease liability	$ 116
Operating Leases
2019		$ 305
2020		236
2021		186
2022		145
2023		102
Thereafter		326
Total reported lease liability		$ 1,300