CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating Revenues
Total Operating Revenues	$ 2,288	$ 2,156	$ 4,164	$ 3,988
Operating Expenses
Wages and benefits	567	544	1,124	1,080
Variable incentive pay	44	38	79	77
Aircraft fuel, including hedging gains and losses	502	475	922	884
Aircraft maintenance	115	106	235	213
Aircraft rent	82	77	165	151
Landing fees and other rentals	113	110	245	236
Contracted services	70	76	142	157
Selling expenses	87	88	159	166
Depreciation and amortization	105	97	211	191
Food and beverage service	53	55	102	105
Third-party regional carrier expense	42	39	83	76
Other	136	141	274	282
Special items - merger-related costs	8	39	34	45
Special items—other	0	0	0	25
Total Operating Expenses	1,924	1,885	3,775	3,688
Operating Income	364	271	389	300
Nonoperating Income (Expense)
Interest income	11	10	20	18
Interest expense	(20)	(25)	(42)	(49)
Interest capitalized	3	4	7	9
Other—net	(7)	(1)	(17)	(13)
Nonoperating Income (Expense) Total	(13)	(12)	(32)	(35)
Income Before Income Tax	351	259	357	265
Income tax expense	89	66	91	68
Net Income	$ 262	$ 193	$ 266	$ 197
Basic Earnings Per Share (usd per share)	$ 2.12	$ 1.57	$ 2.15	$ 1.60
Diluted Earnings Per Share (usd per share)	$ 2.11	$ 1.56	$ 2.14	$ 1.59
Shares used for computation:
Basic shares (shares)	123,418	123,268	123,355	123,212
Diluted shares (shares)	124,301	124,036	124,179	123,953
Passenger Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,111	$ 1,997	$ 3,827	$ 3,681
Passenger Revenue [Member] | Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	2,111	1,997	3,827	3,681
Mileage Plan Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	290	275	553	521
Mileage Plan Revenue [Member] | Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	172	167	325	306
Mileage Plan Revenue [Member] | Mileage plan other revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	118	108	228	215
Cargo and Other Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	59	51	109	92
Cargo and Other Revenue [Member] | Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 59	$ 51	$ 109	$ 92