Revenue - Passenger Revenue Breakout (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Operating Revenue	$ 1,793	$ 5,639	$ 7,035	$ 16,698
Passenger Revenue Non Loyalty
Disaggregation of Revenue [Line Items]
Operating Revenue	1,183	4,400	4,966	13,126
Passenger Loyalty Air Transportation
Disaggregation of Revenue [Line Items]
Operating Revenue	205	657	747	1,814
Passenger Ancillary Sold Separately
Disaggregation of Revenue [Line Items]
Operating Revenue	66	173	290	522
Passenger
Disaggregation of Revenue [Line Items]
Operating Revenue	$ 1,454	$ 5,230	$ 6,003	$ 15,462