CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating Revenues
Total Operating Revenues	$ 421.0	$ 2,288.0	$ 2,057.0	$ 4,164.0
Costs and Expenses, Total	709.0	1,924.0	2,666.0	3,775.0
Wages and benefits	472.0	567.0	1,084.0	1,124.0
Variable incentive pay	16.0	44.0	23.0	79.0
Aircraft fuel, including hedging gains and losses	59.0	502.0	443.0	922.0
Aircraft maintenance	45.0	115.0	160.0	235.0
Aircraft rent	74.0	82.0	155.0	165.0
Landing fees and other rentals	83.0	113.0	214.0	245.0
Contracted services	30.0	70.0	102.0	142.0
Selling expenses	4.0	87.0	59.0	159.0
Depreciation and amortization	107.0	105.0	215.0	211.0
Food and beverage service	7.0	53.0	56.0	102.0
Third-party regional carrier expense	26.0	42.0	63.0	83.0
Other	78.0	136.0	221.0	274.0
Special items - merger-related costs	1.0	8.0	4.0	34.0
Special items—other		0.0	229.0	0.0
Operating Income (Loss)	(288.0)	364.0	(609.0)	389.0
Nonoperating Income (Expense)
Interest income	7.0	11.0	16.0	20.0
Interest capitalized	1.0	3.0	4.0	7.0
Other—net	6.0	(7.0)	11.0	(17.0)
Nonoperating Income (Expense) Total	(3.0)	(13.0)	1.0	(32.0)
Income (Loss) Before Income Tax	(291.0)	351.0	(608.0)	357.0
Income tax (benefit) expense	(77.0)	89.0	(162.0)	91.0
Net Income (Loss)	$ (214.0)	$ 262.0	$ (446.0)	$ 266.0
Basic Earnings Per Share (usd per share)	$ (1.74)	$ 2.12	$ (3.62)	$ 2.15
Diluted Earnings Per Share (usd per share)	$ (1.73)	$ 2.11	$ (3.60)	$ 2.14
Shares used for computation:
Basic shares (shares)	123,296	123,418	123,058	123,355
Diluted shares (shares)	123,965	124,301	123,685	124,179
Special items - Impairment charges and other	$ 69.0		$ 229.0	$ 0.0
Increase (Decrease) in Contract with Customer, Liability			231.0	385.0
Interest Costs Incurred	17.0	$ 20.0	30.0	42.0
PSPGrantRecognized	(362.0)	0.0	(362.0)	0.0
ProceedsFromPayrollSupportProgramGrant			723.0	0.0
Passenger Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	309.0	2,111.0	1,790.0	3,827.0
Passenger Revenue [Member] | Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	309.0	2,111.0	1,790.0	3,827.0
Mileage Plan Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	129.0	290.0	390.0	553.0
Mileage Plan Revenue [Member] | Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	56.0	172.0	208.0	325.0
Mileage Plan Revenue [Member] | Mileage plan other revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	73.0	118.0	182.0	228.0
Cargo and Other Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	39.0	59.0	85.0	109.0
Cargo and Other Revenue [Member] | Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 39.0	$ 59.0	$ 85.0	$ 109.0