Significant Accounting Policies - Roll Forward of Frequent Flier Deferred Revenue (Details) - Frequent Flyer - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Movement in Deferred Revenue [Roll Forward]
Total Frequent flyer deferred revenue - beginning balance	$ 6,675	$ 6,282
Total miles awarded	3,297	2,558
Travel miles redeemed	(2,723)	(2,079)
Non-travel miles redeemed	(106)	(86)
Total Frequent flyer deferred revenue - ending balance	$ 7,143	$ 6,675