Leases - Components of Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Leases [Abstract]
Operating Lease Expense	$ 74	$ 148
Finance Lease Expense:
Amortization of ROU Assets	3	5
Interest on Lease Liabilities	5	10
Short Term Lease Expense	2	3
Variable Lease Expense	1	3
Sublease Income	(4)	(8)
Total Lease Expense	$ 81	$ 161