OPERATING SEGMENT INFORMATION (Tables) - USD ($)
$ in Millions

3 Months Ended

9 Months Ended

Sep. 30, 2023

Sep. 30, 2022

Sep. 30, 2023

Sep. 30, 2022

Segment Reporting [Abstract]

Schedule of Segment Reporting Information, by Segment

Operating segment information is as follows (in millions):

	Three Months Ended September 30, 2023
	Mainline		Regional		Horizon		Consolidating & Other(a)		Air Group Adjusted(b)			Special Items(c)		Consolidated
Operating Revenue
Passenger revenue	$	2,225	$	393	$	—	$	—	$	2,618		$	—	$	2,618
CPA revenue	—		—		104		(104)		—			—		—
Mileage Plan other revenue	146		13		—		—		159			—		159
Cargo and other revenue	60		—		—		2		62			—		62
Total Operating Revenue	2,431		406		104		(102)		2,839			—		2,839
Operating Expenses
Operating expenses, excluding fuel	1,484		297		89		(92)		1,778			156		1,934
Fuel expense	621		108		—		—		729			(35)		694
Total Operating Expenses	2,105		405		89		(92)		2,507			121		2,628
Non-operating Income (Expense)	—		—		(11)		1		(10)			(8)		(18)
Income (Loss) Before Income Tax	$	326	$	1	$	4	$	(9)	$	322		$	(129)	$	193
Pretax Margin									11.4		%			6.8		%
	Three Months Ended September 30, 2022
	Mainline		Regional		Horizon		Consolidating & Other(a)		Air Group Adjusted(b)			Special Items(c)		Consolidated
Operating Revenue
Passenger revenue	$	2,217	$	398	$	—	$	—	$	2,615		$	—	$	2,615
CPA revenue	—		—		93		(93)		—			—		—
Mileage Plan other revenue	133		13		—		—		146			—		146
Cargo and other revenue	65		—		—		2		67			—		67
Total Operating Revenue	2,415		411		93		(91)		2,828			—		2,828
Operating Expenses
Operating expenses, excluding fuel	1,352		292		94		(94)		1,644			245		1,889
Fuel expense	625		121		—		—		746			131		877
Total Operating Expenses	1,977		413		94		(94)		2,390			376		2,766
Non-operating Income (Expense)	8		—		(5)		—		3			—		3
Income (Loss) Before Income Tax	$	446	$	(2)	$	(6)	$	3	$	441		$	(376)	$	65
Pretax Margin									15.6		%			2.3		%

	Nine Months Ended September 30, 2023
	Mainline		Regional		Horizon		Consolidating & Other(a)		Air Group Adjusted(b)			Special Items(c)		Consolidated
Operating Revenue
Passenger revenue	$	6,143	$	1,057	$	—	$	—	$	7,200		$	—	$	7,200
CPA revenue	—		—		274		(274)		—			—		—
Mileage Plan other revenue	447		36		—		—		483			—		483
Cargo and other revenue	184		—		—		6		190			—		190
Total Operating Revenue	6,774		1,093		274		(268)		7,873			—		7,873
Operating Expenses
Operating expenses, excluding fuel	4,342		832		260		(261)		5,173			406		5,579
Fuel expense	1,672		274		—		—		1,946			(14)		1,932
Total Operating Expenses	6,014		1,106		260		(261)		7,119			392		7,511
Non-operating Income (Expense)	(3)		—		(29)		3		(29)			(14)		(43)
Income (Loss) Before Income Tax	$	757	$	(13)	$	(15)	$	(4)	$	725		$	(406)	$	319
Pretax Margin									9.2		%			4.1		%
	Nine Months Ended September 30, 2022
	Mainline		Regional		Horizon		Consolidating & Other(a)		Air Group Adjusted(b)			Special Items(c)		Consolidated
Operating Revenue
Passenger revenue	$	5,488	$	1,056	$	—	$	—	$	6,544		$	—	$	6,544
CPA revenue	—		—		288		(288)		—			—		—
Mileage Plan other revenue	392		41		—		—		433			—		433
Cargo and other revenue	186		—		—		4		190			—		190
Total Operating Revenue	6,066		1,097		288		(284)		7,167			—		7,167
Operating Expenses
Operating expenses, excluding fuel	3,808		843		291		(288)		4,654			466		5,120
Fuel expense	1,623		313		—		—		1,936			64		2,000
Total Operating Expenses	5,431		1,156		291		(288)		6,590			530		7,120
Non-operating Income (Expense)	12		—		(15)		—		(3)			—		(3)
Income (Loss) Before Income Tax	$	647	$	(59)	$	(18)	$	4	$	574		$	(530)	$	44
Pretax Margin									8.0		%			0.6		%

(a)Includes consolidating entries, Air Group parent company, McGee Air Services, and other immaterial business units.

(b)The Air Group Adjusted column represents the financial information that is reviewed by management to assess performance of operations and determine capital allocation and excludes certain charges.

(c)Includes special items and mark-to-market fuel hedge accounting adjustments.

Total assets were as follows (in millions):

	September 30, 2023		December 31, 2022
Mainline	$	20,468	$	19,733
Horizon	1,320		1,157
Consolidating & Other	(6,623)		(6,704)
Consolidated	$	15,165	$	14,186

Nonoperating Income (Expense)

$ (18)

$ 3

$ (43)

$ (3)

Interest income

23

17

62

35

Operating Expenses, Excluding Fuel

1,934

1,889

5,579

5,120

Economic fuel

694

877

1,932

2,000

Operating Expenses

2,628

2,766

7,511

7,120

Income (Loss) Before Income Tax

$ 193

$ 65

$ 319

$ 44

Pretax Margin, GAAP

6.80%

2.30%

4.10%

0.60%

Pretax Margin, Adjusted

11.40%

15.60%

9.20%

8.00%