Leases - Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Leases [Abstract]
Operating and short-term lease cost	$ 92	$ 196
Finance lease cost:
Amortization of right-of-use assets	3	7
Interest on lease liability	3	6
Total finance lease cost	6	13
Total lease cost	$ 98	$ 209