CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,897	$ 2,838	$ 5,129	$ 5,034
Operating Expenses
Wages and benefits	782	754	1,586	1,477
Variable incentive pay	49	57	93	104
Aircraft fuel, including hedging gains and losses	615	573	1,180	1,238
Aircraft maintenance	129	125	251	249
Aircraft rent	46	54	93	113
Landing fees and other rentals	173	167	338	319
Contracted services	106	95	203	190
Selling expenses	84	81	161	147
Depreciation and amortization	128	113	254	217
Food and beverage service	67	60	125	114
Third-party regional carrier expense	64	54	118	106
Other	186	182	391	359
Special items - operating	146	186	180	250
Costs and Expenses, Total	2,575	2,501	4,973	4,883
Operating Income (Loss)	322	337	156	151
Nonoperating Income (Expense)
Interest income	24	22	41	39
Interest expense	(36)	(28)	(71)	(56)
Interest capitalized	6	7	12	14
Special items - net non-operating	0	(6)	0	(6)
Other—net	0	(7)	0	(16)
Nonoperating Income (Expense) Total	(6)	(12)	(18)	(25)
Income (Loss) Before Income Tax	316	325	138	126
Income tax (benefit) expense	96	85	50	28
Net Income (Loss)	$ 220	$ 240	$ 88	$ 98
Basic Earnings Per Share (usd per share)	$ 1.74	$ 1.88	$ 0.70	$ 0.77
Diluted Earnings Per Share (usd per share)	$ 1.71	$ 1.86	$ 0.69	$ 0.76
Shares used for computation:
Basic shares (shares)	126,337,000	127,440,000	126,153,000	127,470,000
Diluted shares (shares)	128,310,000	128,919,000	127,857,000	128,860,000
Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,651	$ 2,598	$ 4,655	$ 4,582
Mileage plan other revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	174	170	338	324
Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	72	70	136	128
Passenger Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	2,651	2,598	4,655	4,582
Passenger Revenue [Member] | Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	2,651	2,598	4,655	4,582
Mileage Plan Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	464	438	876	824
Mileage Plan Revenue [Member] | Mileage plan other revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	174	170	338	324
Cargo and Other Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	72	70	136	128
Cargo and Other Revenue [Member] | Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 72	$ 70	$ 136	$ 128