CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Revenues
Total Operating Revenues	$ 2,212	$ 2,110	$ 6,200	$ 5,952
Operating Expenses
Wages and benefits	549	477	1,629	1,397
Variable incentive pay	27	40	104	98
Aircraft fuel, including hedging gains and losses	513	368	1,397	1,051
Aircraft maintenance	107	88	320	271
Aircraft rent	82	70	233	204
Landing fees and other rentals	135	124	371	338
Contracted services	70	76	227	234
Selling expenses	79	92	245	277
Depreciation and amortization	99	95	290	275
Food and beverage service	53	50	158	145
Third-party regional carrier expense	38	30	114	84
Other	141	150	423	421
Special items—merger-related costs	22	23	67	86
Special items—other	0	0	25	0
Total Operating Expenses	1,915	1,683	5,603	4,881
Operating Income	297	427	597	1,071
Nonoperating Income (Expense)
Interest income	11	9	29	25
Interest expense	(22)	(26)	(71)	(77)
Interest capitalized	5	5	14	13
Other—net	(7)	2	(20)	1
Nonoperating Income (Expense) Total	(13)	(10)	(48)	(38)
Income Before Income Tax	284	417	549	1,033
Income tax expense	67	158	135	388
Net Income	$ 217	$ 259	$ 414	$ 645
Basic Earnings Per Share (usd per share)	$ 1.76	$ 2.10	$ 3.36	$ 5.22
Diluted Earnings Per Share (usd per share)	$ 1.75	$ 2.09	$ 3.34	$ 5.19
Shares used for computation:
Basic shares (shares)	123,224	123,467	123,216	123,501
Diluted shares (shares)	123,864	124,220	123,804	124,341
Cash dividend declared per share (usd per share)	$ 0.32	$ 0.3	$ 0.96	$ 0.90
Passenger Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,043	$ 1,958	$ 5,725	$ 5,505
Passenger Revenue [Member] | Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	2,043	1,958	5,725	5,505
Mileage Plan Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	267	239	788	719
Mileage Plan Revenue [Member] | Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	153	134	459	405
Mileage Plan Revenue [Member] | Mileage plan other revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	114	105	329	314
Cargo and Other Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	55	47	146	133
Cargo and Other Revenue [Member] | Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 55	$ 47	$ 146	$ 133