Leases - Maturity of Lease Liabilities (Details) $ in Millions	Mar. 31, 2019 USD ($)
Operating Leases
Remainder of 2019	$ 266
2020	342
2021	313
2022	275
2023	243
After 2023	1,015
Total lease payments	2,454
Less: Interest	(256)
Lease liability	2,198
Finance Leases
Remainder of 2019	31
2020	36
2021	27
2022	6
2023	2
After 2023	12
Total lease payments	114
Less: Interest	(5)
Lease liability	109
Total Leases
Remainder of 2019	297
2020	378
2021	340
2022	281
2023	245
After 2023	1,027
Total lease payments	$ 2,568