CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,839	$ 2,828	$ 7,873	$ 7,167
Operating Expenses
Wages and benefits	782	686	2,259	1,931
Variable incentive pay	45	48	149	140
Aircraft fuel, including hedging gains and losses	694	877	1,932	2,000
Aircraft maintenance	118	92	367	331
Aircraft rent	48	76	161	222
Landing fees and other rentals	183	161	502	435
Contracted services	100	83	290	243
Selling expenses	84	82	231	218
Depreciation and amortization	113	104	330	310
Food and beverage service	62	52	176	143
Third-party regional carrier expense	58	53	164	145
Other	185	207	544	536
Special items - Impairment charges and other	156	155	355	376
Special items - labor and related		90	51	90
Operating Expenses	2,628	2,766	7,511	7,120
Costs and Expenses, Total	2,628	2,766	7,511	7,120
Operating Income (Loss)	211	62	362	47
Nonoperating Income (Expense)
Interest income	23	17	62	35
Interest expense	(34)	(31)	(90)	(84)
Interest capitalized	7	3	21	8
Special items - net non-operating	(8)	0	(14)	0
Other—net	(6)	14	(22)	38
Nonoperating Income (Expense) Total	(18)	3	(43)	(3)
Income (Loss) Before Income Tax	193	65	319	44
Income tax (benefit) expense	54	25	82	8
Net Income (Loss)	$ 139	$ 40	$ 237	$ 36
Basic Earnings Per Share (usd per share)	$ 1.09	$ 0.32	$ 1.86	$ 0.28
Diluted Earnings Per Share (usd per share)	$ 1.08	$ 0.31	$ 1.84	$ 0.28
Shares used for computation:
Basic shares (shares)	127,187,000	126,783,000	127,375,000	126,440,000
Diluted shares (shares)	129,188,000	128,370,000	129,085,000.000	128,087,000.000
Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,618	$ 2,615	$ 7,200	$ 6,544
Mileage plan other revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	159	146	483	433
Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	62	67	190	190
Passenger Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	2,618	2,615	7,200	6,544
Passenger Revenue [Member] | Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	2,618	2,615	7,200	6,544
Mileage Plan Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	416	382	1,240	1,104
Mileage Plan Revenue [Member] | Mileage plan other revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	159	146	483	433
Cargo and Other Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	62	67	190	190
Cargo and Other Revenue [Member] | Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 62	$ 67	$ 190	$ 190