Leases - Components of Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Finance lease cost:
Amortization of right-of-use assets	$ 22	$ 43
Interest on lease liabilities	7	12
Operating lease cost	78	164
Short-term lease cost	19	32
Variable lease cost	1	2
Sublease income	(4)	(8)
Total lease costs, net	$ 123	$ 245