Revenue - Air Traffic Liability - Loyalty Program Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Movement in Deferred Revenue
Air traffic liability - loyalty program - beginning balance	$ 3,171	$ 2,799	$ 3,011	$ 2,667
Amounts deferred associated with points awarded	757	719	1,468	1,349
Revenue recognized from points redeemed - Passenger	(622)	(588)	(1,158)	(1,079)
Revenue recognized from points redeemed - Other	(17)	(11)	(32)	(18)
Air traffic liability - loyalty program - ending balance	$ 3,289	$ 2,919	$ 3,289	$ 2,919