Leases - Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Leases [Abstract]
Operating Lease Cost	$ 30	$ 81
Finance Lease Cost
Amortization Expense	10	27
Interest Expense	3	10
Short-term Lease Cost	88	357
Sublease Income	(1)	(3)
Total Lease Cost	$ 130	$ 472