Revenue - Air Traffic Liability - Loyalty Program Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Movement in Deferred Revenue
Air traffic liability - loyalty program - beginning balance	$ 3,011	$ 2,667
Amounts deferred associated with points awarded	711	634
Revenue recognized from points redeemed - Passenger	(535)	(491)
Revenue recognized from points redeemed - Other	(16)	(11)
Air traffic liability - loyalty program - ending balance	$ 3,171	$ 2,799