Leases - Future Minimum Payments (Details) $ in Millions	Dec. 31, 2018 USD ($)
Leases [Abstract]
Operating Leases, 2019	$ 400
Operating Leases, 2020	496
Operating Leases, 2021	421
Operating Leases, 2022	328
Operating Leases, 2023	289
Operating Leases, Thereafter	787
Operating Leases, Total lease payments	2,721
Capital Leases, 2019	72
Capital Leases, 2020	69
Capital Leases, 2021	200
Capital Leases, 2022	35
Capital Leases, 2023	28
Capital Leases, Thereafter	101
Capital Leases, Total lease payments	505
Capital Leases, Less amount representing interest	(86)
Capital Leases, Total	$ 419