Leases - Maturities of Lease Liabilities (Details) $ in Millions	Mar. 31, 2019 USD ($)
Operating Leases Future Minimum Rental Payments
Remainder of 2019	$ 108
2020	146
2021	130
2022	113
2023	97
Thereafter	734
Total lease payments	1,328
Less: Imputed interest	371
Present value of lease liabilities	957
Legally binding lease payments for leases signed but not yet commenced	6
Finance Leases
Remainder of 2019	1
2020	1
2021	0
2022	0
2023	0
Thereafter	12
Total lease payments	14
Less: Imputed interest	10
Present value of lease liabilities	$ 4