Leases Components of Lease Cost (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Short-term Lease, Cost		$ 1	$ 4
Variable Lease, Cost		1,260	1,377
Sublease Income		78	97
Finance Lease, Right-of-Use Asset, Amortization		113	116
Finance Lease, Interest Expense		22	26
Lease, Cost		135	142
Other Property
Operating Lease, Cost		89	89
Type of Aircraft [Domain]
Operating Lease, Cost	[1]	$ 216	$ 182

[1] Net of sublease income of $78 million and $97 million for the years ended December 31, 2020 and 2019.