OPERATING SEGMENT INFORMATION (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of Operating Segments \| segment			3
Operating Revenues
Total Operating Revenues	$ 701.0	$ 2,389.0	$ 2,758.0	$ 6,553.0
Operating expenses
Operating Expenses, Excluding Fuel	1,147.0	1,481.0	3,370.0	4,334.0
Economic fuel	125.0	486.0	568.0	1,408.0
Nonoperating Income (Expense)
Interest income	7.0	11.0	23.0	31.0
Interest expense				(60.0)
Interest Costs Capitalized	4.0	4.0	8.0	11.0
Other	5.0	(3.0)	16.0	(20.0)
Nonoperating Income (Expense) Total	(18.0)	(6.0)	(17.0)	(38.0)
Income (loss) before income tax	(589.0)	416.0	(1,197.0)	773.0
Costs and Expenses, Total	1,272.0	1,967.0	3,938.0	5,742.0
Interest Costs Incurred	34.0	18.0	64.0	60.0
Air Group Adjusted [Member]
Operating Revenues
Total Operating Revenues	701.0	2,389.0	2,758.0	6,553.0
Operating expenses
Operating Expenses, Excluding Fuel	1,101.0	1,476.0	3,453.0	4,295.0
Economic fuel	128.0	486.0	568.0	1,409.0
Nonoperating Income (Expense)
Interest income	7.0	11.0	23.0	31.0
Interest expense				(60.0)
Interest Costs Capitalized	4.0	4.0	8.0	11.0
Other	5.0	(3.0)	16.0	(20.0)
Nonoperating Income (Expense) Total	(18.0)	(6.0)	(17.0)	(38.0)
Income (loss) before income tax	(546.0)	421.0	(1,280.0)	811.0
Costs and Expenses, Total	1,229.0	1,962.0	4,021.0	5,704.0
Interest Costs Incurred	34.0	18.0	64.0	60.0
Alaska Mainline [Member]
Operating Revenues
Total Operating Revenues	511.0	2,015.0	2,207.0	5,514.0
Operating expenses
Operating Expenses, Excluding Fuel	872.0	1,226.0	2,777.0	3,545.0
Economic fuel	90.0	411.0	448.0	1,191.0
Nonoperating Income (Expense)
Interest income	8.0	17.0	33.0	50.0
Interest Costs Capitalized	4.0	4.0	8.0	11.0
Other	4.0	(3.0)	16.0	(20.0)
Nonoperating Income (Expense) Total	(12.0)	0.0	(1.0)	(17.0)
Income (loss) before income tax	(463.0)	378.0	(1,019.0)	761.0
Costs and Expenses, Total	962.0	1,637.0	3,225.0	4,736.0
Interest Costs Incurred	28.0	18.0	58.0	58.0
Alaska Regional [Member]
Operating Revenues
Total Operating Revenues	190.0	373.0	549.0	1,035.0
Operating expenses
Operating Expenses, Excluding Fuel	248.0	275.0	727.0	817.0
Economic fuel	38.0	75.0	120.0	218.0
Nonoperating Income (Expense)
Interest income	0.0	0.0	0.0	0.0
Interest expense				0.0
Interest Costs Capitalized	0.0	0.0	0.0	0.0
Other	0.0	0.0	0.0	0.0
Nonoperating Income (Expense) Total	0.0	0.0	0.0	0.0
Income (loss) before income tax	(96.0)	23.0	(298.0)	0.0
Costs and Expenses, Total	286.0	350.0	847.0	1,035.0
Interest Costs Incurred	0.0	0.0	0.0	0.0
Horizon [Member]
Operating Revenues
Total Operating Revenues	95.0	112.0	281.0	341.0
Operating expenses
Operating Expenses, Excluding Fuel	78.0	94.0	238.0	286.0
Economic fuel	0.0	0.0	0.0	0.0
Nonoperating Income (Expense)
Interest income	0.0	0.0	0.0	0.0
Interest expense				(22.0)
Interest Costs Capitalized	0.0	0.0	0.0	0.0
Other	0.0	0.0	0.0	0.0
Nonoperating Income (Expense) Total	(6.0)	(7.0)	(16.0)	(22.0)
Income (loss) before income tax	11.0	11.0	27.0	33.0
Costs and Expenses, Total	78.0	94.0	238.0	286.0
Interest Costs Incurred	6.0	7.0	16.0	22.0
Intersegment Elimination [Member]
Operating Revenues
Total Operating Revenues	(95.0)	(111.0)	(279.0)	(337.0)
Operating expenses
Operating Expenses, Excluding Fuel	(97.0)	(119.0)	(289.0)	(353.0)
Economic fuel	0.0	0.0	0.0	0.0
Nonoperating Income (Expense)
Interest income	(1.0)	(6.0)	(10.0)	(19.0)
Interest expense				20.0
Interest Costs Capitalized	0.0	0.0	0.0	0.0
Other	1.0	0.0	0.0	0.0
Nonoperating Income (Expense) Total	0.0	1.0	0.0	1.0
Income (loss) before income tax	2.0	9.0	10.0	17.0
Costs and Expenses, Total	(97.0)	(119.0)	(289.0)	(353.0)
Interest Costs Incurred	0.0	(7.0)	(10.0)	(20.0)
Special Revenue and Charges [Member]
Operating Revenues
Total Operating Revenues	0.0	0.0	0.0	0.0
Operating expenses
Operating Expenses, Excluding Fuel	46.0	5.0	(83.0)	39.0
Economic fuel	(3.0)	0.0	0.0	(1.0)
Nonoperating Income (Expense)
Interest income	0.0	0.0	0.0	0.0
Interest expense				0.0
Interest Costs Capitalized	0.0	0.0	0.0	0.0
Other	0.0	0.0	0.0	0.0
Nonoperating Income (Expense) Total	0.0	0.0	0.0	0.0
Income (loss) before income tax	(43.0)	(5.0)	83.0	(38.0)
Costs and Expenses, Total	43.0	5.0	(83.0)	38.0
Interest Costs Incurred	0.0	0.0	0.0	0.0
Passenger [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	572.0	2,211.0	2,362.0	6,038.0
Passenger [Member] \| Air Group Adjusted [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	572.0	2,211.0	2,362.0	6,038.0
Passenger [Member] \| Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	401.0	1,850.0	1,860.0	5,039.0
Passenger [Member] \| Alaska Regional [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	171.0	361.0	502.0	999.0
Passenger [Member] \| Horizon [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0	0.0	0.0
Passenger [Member] \| Intersegment Elimination [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0	0.0	0.0
Passenger [Member] \| Special Revenue and Charges [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0	0.0	0.0
Capacity Purchase Agreements [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0	0.0	0.0
Capacity Purchase Agreements [Member] \| Air Group Adjusted [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0	0.0	0.0
Capacity Purchase Agreements [Member] \| Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0	0.0	0.0
Capacity Purchase Agreements [Member] \| Alaska Regional [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0	0.0	0.0
Capacity Purchase Agreements [Member] \| Horizon [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	95.0	112.0	281.0	340.0
Capacity Purchase Agreements [Member] \| Intersegment Elimination [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	(95.0)	(112.0)	(281.0)	(340.0)
Capacity Purchase Agreements [Member] \| Special Revenue and Charges [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0	0.0	0.0
Mileage plan other revenue [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	84.0	118.0	266.0	346.0
Mileage plan other revenue [Member] \| Air Group Adjusted [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	84.0	118.0	266.0	346.0
Mileage plan other revenue [Member] \| Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	65.0	107.0	219.0	312.0
Mileage plan other revenue [Member] \| Alaska Regional [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	19.0	11.0	47.0	34.0
Mileage plan other revenue [Member] \| Horizon [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0	0.0	0.0
Mileage plan other revenue [Member] \| Intersegment Elimination [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0	0.0	0.0
Mileage plan other revenue [Member] \| Special Revenue and Charges [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0	0.0	0.0
Cargo and Freight [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	45.0	60.0	130.0	169.0
Cargo and Freight [Member] \| Air Group Adjusted [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	45.0	60.0	130.0	169.0
Cargo and Freight [Member] \| Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	45.0	58.0	128.0	163.0
Cargo and Freight [Member] \| Alaska Regional [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	1.0	0.0	2.0
Cargo and Freight [Member] \| Horizon [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0	0.0	1.0
Cargo and Freight [Member] \| Intersegment Elimination [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	1.0	2.0	3.0
Cargo and Freight [Member] \| Special Revenue and Charges [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	$ 0.0	$ 0.0	$ 0.0	$ 0.0

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