Leases - Future Maturities of Lease Liabilities - ASC 842 (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Operating Leases
2019 (excluding the six months ended June 30)	$ 128
2020	222
2021	174
2022	123
2023	96
Thereafter	369
Total Lease Payments	1,112
Less: Imputed Interest	248
Total	864
Finance Leases
2019 (excluding the six months ended June 30)	12
2020	24
2021	35
2022	21
2023	20
Thereafter	713
Total Lease Payments	825
Less: Imputed Interest	577
Total	$ 248	$ 37