Revenue - Air Traffic Liability - Loyalty Program Rollforward (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Movement in Deferred Revenue
Air traffic liability - loyalty program - beginning balance	$ 3,289	$ 2,919	$ 3,011	$ 2,667
Amounts deferred associated with points awarded	727	669	2,195	2,027
Revenue recognized from points redeemed - Passenger	(657)	(623)	(1,814)	(1,702)
Revenue recognized from points redeemed - Other	(20)	(17)	(53)	(44)
Air traffic liability - loyalty program - ending balance	$ 3,339	$ 2,948	$ 3,339	$ 2,948

$ 3,289

$ 2,919

$ 3,011

$ 2,667

(657)

(623)

(1,814)

(1,702)

$ 3,339

$ 2,948

$ 3,339

$ 2,948