Debt - Schedule of Debt Obligations (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024	Sep. 30, 2024	May 31, 2024
Debt Instrument [Line Items]
Long-term debt, gross	$ 565		$ 507
Less: current maturities of long-term debt, net	(326)		(261)
Less: total debt acquisition costs and other discounts, net	(5)		(5)
Long-term debt, net	234		$ 241
Principal repayments on debt	$ 43	$ 161
CARES Act Credit Agreement, Warrants
Debt Instrument [Line Items]
Warrants to acquire common stock (in shares)	1,873,332		3,117,940
Exercise price of warrants (in dollars per share)	$ 6.95
Warrants exercised (in shares)	1,244,608
Number of securities called by warrants (in shares)	248,893
Warrant settled, cash potion (less than)	$ 1
Secured Debt | Pre-delivery Credit Facilities
Debt Instrument [Line Items]
Long-term debt, gross	386		$ 329
Amount of unsecured borrowings available	476
Secured Debt | Building notes
Debt Instrument [Line Items]
Long-term debt, gross	12		12
Unsecured low interest loan amount				$ 12
Secured Debt | Building Note Tranche One
Debt Instrument [Line Items]
Unsecured low interest loan amount					$ 6
Secured Debt | Building Note Tranche Two
Debt Instrument [Line Items]
Unsecured low interest loan amount				$ 6
Secured Debt | Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt, gross	0		0
Amount of unsecured borrowings available	205
Unsecured Debt | Affinity card advance purchase of miles
Debt Instrument [Line Items]
Long-term debt, gross	101		100
Amount of unsecured borrowings available	200
Unsecured Debt | PSP Promissory Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 66		$ 66
Interest rate	1.00%
Interest rate period	5 years
Debt instrument, variable interest rate	2.00%
Unsecured Debt | PSP1 Promissory Note
Debt Instrument [Line Items]
Loan term	10 years