Revenue - Air Traffic Liability - Loyalty Program Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Movement in Deferred Revenue
Air traffic liability - loyalty program - beginning balance	$ 2,919	$ 2,586	$ 2,667	$ 2,485
Amounts deferred associated with points awarded	669	621	2,027	1,846
Revenue recognized from points redeemed - Passenger	(623)	(616)	(1,702)	(1,724)
Revenue recognized from points redeemed - Other	(17)	(9)	(44)	(25)
Air traffic liability - loyalty program - ending balance	$ 2,948	$ 2,582	$ 2,948	$ 2,582