Leases - Future Payments Under Operating Leases (Details) $ in Millions	Jun. 30, 2019 USD ($)
Operating Leases
2019 (excluding six months ended June 30, 2019)	$ 787
2020	1,535
2021	1,356
2022	1,161
2023	988
After 2023	4,180
Total future minimum lease payments	10,007
Less: Imputed interest	(1,603)
Total	$ 8,404