Leases - Future Minimum Lease Payments Under Topic 840 (Details) $ in Millions	Dec. 31, 2018 USD ($)
Capital Leases
2019	$ 61
2020	60
2021	55
2022	52
2023	43
Thereafter	39
Total minimum lease payments	310
Amount representing interest	(21)
Present value of minimum lease payments	289
Operating Leases
2019	577
2020	460
2021	367
2022	288
2023	221
Thereafter	523
Total minimum lease payments	$ 2,436