Leases - Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Leases [Abstract]
Operating and short-term lease cost	$ 157	$ 492
Finance lease cost:
Amortization of right-of-use assets	11	34
Interest on lease liability	2	9
Total finance lease cost	13	43
Total lease cost	$ 170	$ 535