OPERATING SEGMENT INFORMATION (Details) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of Operating Segments \| segment			3
Operating Revenues
Total Operating Revenues	$ 421.0	$ 2,288.0	$ 2,057.0	$ 4,164.0
Operating expenses
Operating Expenses, Excluding Fuel	650.0	1,422.0	2,223.0	2,853.0
Economic fuel	59.0	502.0	443.0	922.0
Nonoperating Income (Expense)
Interest income	7.0	11.0	16.0	20.0
Interest Costs Capitalized	1.0	3.0	4.0	7.0
Other	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
Costs and Expenses, Total	709.0	1,924.0	2,666.0	3,775.0
Interest Costs Incurred	17.0	20.0	30.0	42.0
Air Group Adjusted [Member]
Operating Revenues
Total Operating Revenues	421.0	2,288.0	2,057.0	4,164.0
Operating expenses
Operating Expenses, Excluding Fuel	942.0	1,414.0	2,352.0	2,819.0
Economic fuel	65.0	499.0	440.0	923.0
Nonoperating Income (Expense)
Interest income	7.0	11.0	16.0	20.0
Interest Costs Capitalized	1.0	3.0	4.0	7.0
Other	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	(589.0)	362.0	(734.0)	390.0
Costs and Expenses, Total	1,007.0	1,913.0	2,792.0	3,742.0
Interest Costs Incurred	17.0	20.0	30.0	42.0
Alaska Mainline [Member]
Operating Revenues
Total Operating Revenues	320.0	1,929.0	1,696.0	3,499.0
Operating expenses
Operating Expenses, Excluding Fuel	746.0	1,167.0	1,905.0	2,319.0
Economic fuel	45.0	422.0	358.0	780.0
Nonoperating Income (Expense)
Interest income	11.0	17.0	25.0	33.0
Interest Costs Capitalized	1.0	3.0	4.0	7.0
Other	6.0	(7.0)	12.0	(17.0)
Nonoperating Income (Expense) Total	0.0	(6.0)	11.0	(17.0)
Income (loss) before income tax	(471.0)	334.0	(556.0)	383.0
Costs and Expenses, Total	791.0	1,589.0	2,263.0	3,099.0
Interest Costs Incurred	18.0	19.0	30.0	40.0
Alaska Regional [Member]
Operating Revenues
Total Operating Revenues	101.0	357.0	359.0	662.0
Operating expenses
Operating Expenses, Excluding Fuel	210.0	268.0	479.0	542.0
Economic fuel	20.0	77.0	82.0	143.0
Nonoperating Income (Expense)
Interest income	0.0	0.0	0.0	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	(129.0)	12.0	(202.0)	(23.0)
Costs and Expenses, Total	230.0	345.0	561.0	685.0
Interest Costs Incurred	0.0	0.0	0.0	0.0
Horizon [Member]
Operating Revenues
Total Operating Revenues	81.0	112.0	186.0	229.0
Operating expenses
Operating Expenses, Excluding Fuel	68.0	95.0	160.0	192.0
Economic fuel	0.0	0.0	0.0	0.0
Nonoperating Income (Expense)
Interest income	0.0	0.0	0.0	0.0
Interest Costs Capitalized	0.0	0.0	0.0	0.0
Other	0.0	0.0	0.0	0.0
Nonoperating Income (Expense) Total	(5.0)	(7.0)	(10.0)	(15.0)
Income (loss) before income tax	8.0	10.0	16.0	22.0
Costs and Expenses, Total	68.0	95.0	160.0	192.0
Interest Costs Incurred	5.0	7.0	10.0	15.0
Intersegment Elimination [Member]
Operating Revenues
Total Operating Revenues	(81.0)	(110.0)	(184.0)	(226.0)
Operating expenses
Operating Expenses, Excluding Fuel	(82.0)	(116.0)	(192.0)	(234.0)
Economic fuel	0.0	0.0	0.0	0.0
Nonoperating Income (Expense)
Interest income	(4.0)	(6.0)	(9.0)	(13.0)
Interest Costs Capitalized	0.0	0.0	0.0	0.0
Other	0.0	0.0	(1.0)	0.0
Nonoperating Income (Expense) Total	2.0	0.0	0.0	0.0
Income (loss) before income tax	3.0	6.0	8.0	8.0
Costs and Expenses, Total	(82.0)	(116.0)	(192.0)	(234.0)
Interest Costs Incurred	(6.0)	(6.0)	(10.0)	(13.0)
Special Revenue and Charges [Member]
Operating Revenues
Total Operating Revenues	0.0	0.0	0.0	0.0
Operating expenses
Operating Expenses, Excluding Fuel	(292.0)	8.0	(129.0)	34.0
Economic fuel	(6.0)	3.0	3.0	(1.0)
Nonoperating Income (Expense)
Interest income	0.0	0.0	0.0	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	298.0	(11.0)	126.0	(33.0)
Costs and Expenses, Total	(298.0)	11.0	(126.0)	33.0
Interest Costs Incurred	0.0	0.0	0.0	0.0
Passenger [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	309.0	2,111.0	1,790.0	3,827.0
Passenger [Member] \| Air Group Adjusted [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	309.0	2,111.0	1,790.0	3,827.0
Passenger [Member] \| Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	225.0	1,767.0	1,459.0	3,189.0
Passenger [Member] \| Alaska Regional [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	84.0	344.0	331.0	638.0
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	81.0	112.0	186.0	228.0
Capacity Purchase Agreements [Member] \| Intersegment Elimination [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	(81.0)	(112.0)	(186.0)	(228.0)
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	73.0	118.0	182.0	228.0
Mileage plan other revenue [Member] \| Air Group Adjusted [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	73.0	118.0	182.0	228.0
Mileage plan other revenue [Member] \| Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	56.0	105.0	154.0	205.0
Mileage plan other revenue [Member] \| Alaska Regional [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	17.0	13.0	28.0	23.0
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	39.0	59.0	85.0	109.0
Cargo and Freight [Member] \| Air Group Adjusted [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	39.0	59.0	85.0	109.0
Cargo and Freight [Member] \| Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	39.0	57.0	83.0	105.0
Cargo and Freight [Member] \| Alaska Regional [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0	0.0	1.0
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	2.0	2.0	2.0
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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