CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,232	$ 2,196
Operating Expenses
Wages and benefits	804	723
Variable incentive pay	44	47
Aircraft fuel, including hedging gains and losses	565	665
Aircraft maintenance	122	124
Aircraft rent	47	59
Landing fees and other rentals	165	152
Contracted services	97	95
Selling expenses	77	66
Depreciation and amortization	126	104
Food and beverage service	58	54
Third-party regional carrier expense	54	52
Other	205	177
Special items - Impairment charges and other	26	13
Special items - merger-related costs	8	0
Special items - labor and related		51
Costs and Expenses, Total	2,398	2,382
Operating Income (Loss)	(166)	(186)
Nonoperating Income (Expense)
Interest income	17	17
Interest expense	(35)	(28)
Interest capitalized	6	7
Other—net	0	(9)
Nonoperating Income (Expense) Total	(12)	(13)
Income (Loss) Before Income Tax	(178)	(199)
Income tax (benefit) expense	(46)	(57)
Net Income (Loss)	$ (132)	$ (142)
Basic Earnings Per Share (usd per share)	$ (1.05)	$ (1.11)
Diluted Earnings Per Share (usd per share)	$ (1.05)	$ (1.11)
Shares used for computation:
Basic shares (shares)	125,970,000	127,501,000
Diluted shares (shares)	125,970,000	127,501,000
Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,004	$ 1,984
Mileage plan other revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	164	154
Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	64	58
Passenger Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	2,004	1,984
Passenger Revenue [Member] | Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	2,004	1,984
Mileage Plan Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	412	386
Mileage Plan Revenue [Member] | Mileage plan other revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	164	154
Cargo and Other Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	64	58
Cargo and Other Revenue [Member] | Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 64	$ 58