CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Revenues
Total Operating Revenues	$ 8,264	$ 7,894	$ 5,925
Operating Expenses
Wages and benefits	2,190	1,931	1,394
Variable incentive pay	147	135	127
Aircraft fuel, including hedging gains and losses	1,936	1,447	831
Aircraft maintenance	435	391	270
Aircraft rent	315	274	114
Landing fees and other rentals	499	460	320
Contracted services	306	314	247
Selling expense	326	368	248
Depreciation and amortization	398	372	363
Cost of Services, Catering	211	195	126
Third-party regional carrier expense	154	121	95
Other operating expenses	572	562	367
Special items - merger-related costs	87	116	117
Special items—other	45	0	0
Total Operating Expenses	7,621	6,686	4,619
Operating Income	643	1,208	1,306
Nonoperating Income (Expense)
Interest income	38	34	27
Interest expense	(91)	(103)	(55)
Interest capitalized	18	17	25
Other—net	(23)	3	13
Nonoperating Income (Expense) Total	(58)	(49)	10
Income before income tax	585	1,159	1,316
Income Tax Expense, Before Tax Cuts and Jobs Act of 2017	148	436	502
Special tax expense (benefit)	0	(237)	17
Income tax expense	148	199	519
Net Income	$ 437	$ 960	$ 797
Basic earnings per share	$ 3.55	$ 7.79	$ 6.45
Diluted earnings per share	$ 3.52	$ 7.75	$ 6.41
Shares used for computation:
Basic	123,230	123,211	123,557
Diluted	123,975	123,854	124,389
Cash dividend declared per share	$ 1.28	$ 1.20	$ 1.10
Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax		$ 7,301	$ 5,392
Mileage Plan Services, Other [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 434	418	370
Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	198	175	163
Passenger Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	7,632	7,301	5,392
Passenger Revenue [Member] | Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	7,632	7,301	5,392
Mileage Plan Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	1,053	959	813
Mileage Plan Revenue [Member] | Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	619	541	443
Mileage Plan Revenue [Member] | Mileage Plan Services, Other [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	434	418	370
Cargo and Other Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	198	175	163
Cargo and Other Revenue [Member] | Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 198	$ 175	$ 163