Leases - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 78	$ 53
Operating cash flows from finance leases	9	0
Financing cash flows from finance leases	105	11
Right-of-use assets obtained in exchange for lease liabilities:
Operating leases	0	56
Finance leases	$ 315	$ 15