Leases - Maturities of Lease Liabilities (Details) $ in Millions	Jun. 30, 2019 USD ($)
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2019 (remaining six months)	$ 155
2020	271
2021	232
2022	203
2023	172
Thereafter	614
Total lease payments	1,647
Less: interest	(416)
Total	1,231
Less: current portion	(269)
Long-term portion	962
Finance Lease, Liability, Payment, Due [Abstract]
2019 (remaining six months)	9
2020	15
2021	16
2022	16
2023	17
Thereafter	165
Total lease payments	238
Less: interest	(76)
Total	162
Less: current portion	(7)
Long-term portion	$ 155