OPERATING SEGMENT INFORMATION (Details) $ in Millions	3 Months Ended
Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of Operating Segments \| segment	3
Operating Revenues
Total Operating Revenues	$ 1,636.0	$ 1,876.0
Operating expenses
Operating Expenses, Excluding Fuel	1,573.0	1,431.0
Economic fuel	384.0	420.0
Nonoperating Income (Expense)
Interest income	9.0	9.0
Interest Costs Capitalized	3.0	4.0
Other	5.0	(10.0)
Nonoperating Income (Expense) Total	4.0	(19.0)
Income (loss) before income tax	(317.0)	6.0
Costs and Expenses, Total	1,957.0	1,851.0
Interest Costs Incurred	13.0	22.0
Air Group Adjusted [Member]
Operating Revenues
Total Operating Revenues	1,636.0	1,876.0
Operating expenses
Operating Expenses, Excluding Fuel	1,410.0	1,405.0
Economic fuel	375.0	424.0
Nonoperating Income (Expense)
Interest income	9.0	9.0
Interest Costs Capitalized	3.0	4.0
Other	5.0	(10.0)
Nonoperating Income (Expense) Total	4.0	(19.0)
Income (loss) before income tax	(145.0)	28.0
Costs and Expenses, Total	1,785.0	1,829.0
Interest Costs Incurred	13.0	22.0
Alaska Mainline [Member]
Operating Revenues
Total Operating Revenues	1,376.0	1,570.0
Operating expenses
Operating Expenses, Excluding Fuel	1,159.0	1,152.0
Economic fuel	313.0	358.0
Nonoperating Income (Expense)
Interest income	14.0	16.0
Interest Costs Capitalized	3.0	4.0
Other	6.0	(10.0)
Nonoperating Income (Expense) Total	11.0	(11.0)
Income (loss) before income tax	(85.0)	49.0
Costs and Expenses, Total	1,472.0	1,510.0
Interest Costs Incurred	12.0	21.0
Alaska Regional [Member]
Operating Revenues
Total Operating Revenues	258.0	305.0
Operating expenses
Operating Expenses, Excluding Fuel	269.0	274.0
Economic fuel	62.0	66.0
Nonoperating Income (Expense)
Interest income	0.0	0.0
Interest Costs Capitalized	0.0	0.0
Other	0.0	0.0
Nonoperating Income (Expense) Total	0.0	0.0
Income (loss) before income tax	(73.0)	(35.0)
Costs and Expenses, Total	331.0	340.0
Interest Costs Incurred	0.0	0.0
Horizon [Member]
Operating Revenues
Total Operating Revenues	105.0	117.0
Operating expenses
Operating Expenses, Excluding Fuel	92.0	97.0
Economic fuel	0.0	0.0
Nonoperating Income (Expense)
Interest income	0.0	0.0
Interest Costs Capitalized	0.0	0.0
Other	0.0	0.0
Nonoperating Income (Expense) Total	(5.0)	(8.0)
Income (loss) before income tax	8.0	12.0
Costs and Expenses, Total	92.0	97.0
Interest Costs Incurred	5.0	8.0
Intersegment Elimination [Member]
Operating Revenues
Total Operating Revenues	(103.0)	(116.0)
Operating expenses
Operating Expenses, Excluding Fuel	(110.0)	(118.0)
Economic fuel	0.0	0.0
Nonoperating Income (Expense)
Interest income	(5.0)	(7.0)
Interest Costs Capitalized	0.0	0.0
Other	(1.0)	0.0
Nonoperating Income (Expense) Total	(2.0)	0.0
Income (loss) before income tax	5.0	2.0
Costs and Expenses, Total	(110.0)	(118.0)
Interest Costs Incurred	(4.0)	(7.0)
Special Revenue and Charges [Member]
Operating Revenues
Total Operating Revenues	0.0	0.0
Operating expenses
Operating Expenses, Excluding Fuel	163.0	26.0
Economic fuel	9.0	(4.0)
Nonoperating Income (Expense)
Interest income	0.0	0.0
Interest Costs Capitalized	0.0	0.0
Other	0.0	0.0
Nonoperating Income (Expense) Total	0.0	0.0
Income (loss) before income tax	(172.0)	(22.0)
Costs and Expenses, Total	172.0	22.0
Interest Costs Incurred	0.0	0.0
Passenger [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	1,481.0	1,716.0
Passenger [Member] \| Air Group Adjusted [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	1,481.0	1,716.0
Passenger [Member] \| Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	1,234.0	1,422.0
Passenger [Member] \| Alaska Regional [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	247.0	294.0
Passenger [Member] \| Horizon [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0
Passenger [Member] \| Intersegment Elimination [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	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
Capacity Purchase Agreements [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	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
Capacity Purchase Agreements [Member] \| Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	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
Capacity Purchase Agreements [Member] \| Horizon [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	105.0	116.0
Capacity Purchase Agreements [Member] \| Intersegment Elimination [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	(105.0)	(116.0)
Capacity Purchase Agreements [Member] \| Special Revenue and Charges [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0
Mileage plan other revenue [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	109.0	110.0
Mileage plan other revenue [Member] \| Air Group Adjusted [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	109.0	110.0
Mileage plan other revenue [Member] \| Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	98.0	100.0
Mileage plan other revenue [Member] \| Alaska Regional [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	11.0	10.0
Mileage plan other revenue [Member] \| Horizon [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	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
Mileage plan other revenue [Member] \| Special Revenue and Charges [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	0.0
Cargo and Freight [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	46.0	50.0
Cargo and Freight [Member] \| Air Group Adjusted [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	46.0	50.0
Cargo and Freight [Member] \| Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	44.0	48.0
Cargo and Freight [Member] \| Alaska Regional [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	1.0
Cargo and Freight [Member] \| Horizon [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0.0	1.0
Cargo and Freight [Member] \| Intersegment Elimination [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	2.0	0.0
Cargo and Freight [Member] \| Special Revenue and Charges [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	$ 0.0	$ 0.0

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