Leases - Future Minimum Lease Payments (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Operating Leases
2019, remaining	$ 90
2020	164
2021	148
2022	142
2023	114
Thereafter	680
Total minimum lease payments	1,338
Less: Amount representing interest	(318)
Present value of minimum lease payments	1,020
Finance Leases
2019, remaining	6
2020	13
2021	13
2022	13
2023	13
Thereafter	165
Total minimum lease payments	223
Less: Amount representing interest	(63)
Present value of minimum lease payments	$ 160	$ 163