CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating Revenues
Total Operating Revenues	$ 2,156	$ 2,102	$ 3,988	$ 3,842
Operating Expenses
Wages and benefits	544	470	1,080	920
Variable incentive pay	38	27	77	58
Aircraft fuel, including hedging gains and losses	475	344	884	683
Aircraft maintenance	106	96	213	183
Aircraft rent	77	69	151	134
Landing fees and other rentals	110	99	236	214
Contracted services	76	77	157	158
Selling expenses	88	102	166	185
Depreciation and amortization	97	90	191	180
Food and beverage service	55	50	105	95
Third-party regional carrier expense	39	27	76	54
Other	141	140	282	271
Special items—merger-related costs	39	24	45	63
Special items—other	0	0	25	0
Total Operating Expenses	1,885	1,615	3,688	3,198
Operating Income	271	487	300	644
Nonoperating Income (Expense)
Interest income	10	9	18	16
Interest expense	(25)	(26)	(49)	(51)
Interest capitalized	4	4	9	8
Other—net	(1)	0	(13)	(1)
Nonoperating Income (Expense) Total	(12)	(13)	(35)	(28)
Income Before Income Tax	259	474	265	616
Income tax expense	66	181	68	230
Net Income	$ 193	$ 293	$ 197	$ 386
Basic Earnings Per Share (usd per share)	$ 1.57	$ 2.37	$ 1.60	$ 3.12
Diluted Earnings Per Share (usd per share)	$ 1.56	$ 2.36	$ 1.59	$ 3.10
Shares used for computation:
Basic shares (shares)	123,268	123,573	123,212	123,534
Diluted shares (shares)	124,036	124,332	123,953	124,374
Cash dividend declared per share (usd per share)	$ 0.32	$ 0.3	$ 0.64	$ 0.60
Passenger Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 1,997	$ 1,945	$ 3,682	$ 3,547
Passenger Revenue [Member] | Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	1,997	1,945	3,682	3,547
Mileage Plan Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	275	252	521	480
Mileage Plan Revenue [Member] | Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	167	143	306	271
Mileage Plan Revenue [Member] | Mileage plan other revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	108	109	215	209
Cargo and Other Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	51	48	91	86
Cargo and Other Revenue [Member] | Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 51	$ 48	$ 91	$ 86