Significant Accounting Policies - Roll Forward of Frequent Flier Deferred Revenue (Details) - Frequent Flyer - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Movement in Deferred Revenue [Roll Forward]
Total Frequent flyer deferred revenue - beginning balance	$ 5,975	$ 5,276
Total miles awarded	1,545	1,336
Travel miles redeemed (Passenger revenue)	(1,171)	(568)
Non-travel miles redeemed (Other operating revenue)	(67)	(69)
Total Frequent flyer deferred revenue - ending balance	$ 6,282	$ 5,975