Leases - Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Leases [Abstract]
Operating Lease Cost	$ 26	$ 51
Finance Lease Cost
Amortization Expense	9	17
Interest Expense	4	7
Short-term Lease Cost	143	269
Variable Lease Cost	0	0
Sublease Income	(1)	(2)
Total Lease Cost	$ 181	$ 342