Leases - Lease Expense (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Leases [Abstract]
Operating Lease Cost	$ 25
Finance Lease Cost
Amortization Expense on ROU Assets	8
Interest Expense on Lease Liabilities	3
Short-term Lease Cost	126
Variable Lease Cost	0
Sublease Income	(1)
Total Lease Cost	$ 161