Leases - Maturities of Lease Liabilities (Details) $ in Millions	Mar. 31, 2019 USD ($)
Operating Leases
2019	$ 463
2020	462
2021	381
2022	301
2023	260
Thereafter	878
Total lease payments	2,745
Less: interest	(683)
Total	2,062
Less: current portion	(561)
Long-term portion	1,501
Finance Leases
2019	38
2020	35
2021	22
2022	20
2023	19
Thereafter	179
Total lease payments	313
Less: interest	(87)
Total	226
Less: current portion	(36)
Long-term portion	$ 190