Leases - Maturities of Lease Liabilities (Details) $ in Millions	Mar. 31, 2019 USD ($)
Operating Lease Liabilities, Payments Due [Abstract]
2019 (remaining nine months)	$ 269
2020	285
2021	244
2022	188
2023	155
Thereafter	590
Total lease payments	1,731
Less: interest	(438)
Total	1,293
Less: current portion	(324)
Long-term portion	969
Finance Lease Liabilities, Payments, Due [Abstract]
2019 (remaining nine months)	12
2020	15
2021	16
2022	16
2023	17
Thereafter	164
Total lease payments	240
Less: interest	(78)
Total	162
Less: current portion	(7)
Long-term portion	$ 155