Leases - Maturities of Lease Liabilities (Details) $ in Millions	Mar. 31, 2019 USD ($)
Leases [Abstract]
Operating Leases, 2019	$ 228
Operating Leases, 2020	510
Operating Leases, 2021	437
Operating Leases, 2022	345
Operating Leases, 2023	298
Operating Leases, Thereafter	802
Operating Leases, Total lease payments	2,620
Operating Leases, Less amount representing interest	(350)
Operating Leases, Total	2,270
Finance Lease, 2019	55
Finance Lease, 2020	69
Finance Lease, 2021	200
Finance Lease, 2022	35
Finance Lease, 2023	28
Finance Lease, Thereafter	101
Finance Lease, Total lease payments	488
Finance Lease, Less amount representing interest	(79)
Finance Lease, Total	$ 409