OPERATING SEGMENT INFORMATION (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of Operating Segments | segment			3
Operating Revenues
Total Operating Revenues	$ 2,389	$ 2,212	$ 6,553	$ 6,200
Operating expenses
Operating Expenses, Excluding Fuel	1,481	1,402	4,334	4,206
Economic fuel	486	513	1,408	1,397
Total Operating Expenses	1,967	1,915	5,742	5,603
Nonoperating Income (Expense)
Interest income	11	11	31	29
Interest expense	(18)	(22)	(60)	(71)
Interest Costs Capitalized	4	5	11	14
Other	(3)	(7)	(20)	(20)
Nonoperating Income (Expense) Total	(6)	(13)	(38)	(48)
Income (loss) before income tax	416	284	773	549
Air Group Adjusted [Member]
Operating Revenues
Total Operating Revenues	2,389	2,212	6,553	6,200
Operating expenses
Operating Expenses, Excluding Fuel	1,476	1,380	4,295	4,114
Economic fuel	486	508	1,409	1,427
Total Operating Expenses	1,962	1,888	5,704	5,541
Nonoperating Income (Expense)
Interest income	11	11	31	29
Interest expense	(18)	(22)	(60)	(71)
Interest Costs Capitalized	4	5	11	14
Other	(3)	(7)	(20)	(20)
Nonoperating Income (Expense) Total	(6)	(13)	(38)	(48)
Income (loss) before income tax	421	311	811	611
Alaska Mainline [Member]
Operating Revenues
Total Operating Revenues	2,015	1,884	5,514	5,322
Operating expenses
Operating Expenses, Excluding Fuel	1,226	1,126	3,545	3,392
Economic fuel	411	438	1,191	1,237
Total Operating Expenses	1,637	1,564	4,736	4,629
Nonoperating Income (Expense)
Interest income	17	15	50	39
Interest expense	(18)	(20)	(58)	(64)
Interest Costs Capitalized	4	4	11	12
Other	(3)	(5)	(20)	(9)
Nonoperating Income (Expense) Total	0	(6)	(17)	(22)
Income (loss) before income tax	378	314	761	671
Alaska Regional [Member]
Operating Revenues
Total Operating Revenues	373	326	1,035	874
Operating expenses
Operating Expenses, Excluding Fuel	275	267	817	755
Economic fuel	75	70	218	190
Total Operating Expenses	350	337	1,035	945
Nonoperating Income (Expense)
Interest income	0	0	0	0
Interest expense	0	0	0	0
Interest Costs Capitalized	0	0	0	0
Other	0	(2)	0	(11)
Nonoperating Income (Expense) Total	0	(2)	0	(11)
Income (loss) before income tax	23	(13)	0	(82)
Horizon [Member]
Operating Revenues
Total Operating Revenues	112	130	341	379
Operating expenses
Operating Expenses, Excluding Fuel	94	118	286	345
Economic fuel	0	0	0	0
Total Operating Expenses	94	118	286	345
Nonoperating Income (Expense)
Interest income	0	0	0	0
Interest expense	(7)	(6)	(22)	(16)
Interest Costs Capitalized	0	1	0	2
Other	0	0	0	0
Nonoperating Income (Expense) Total	(7)	(5)	(22)	(14)
Income (loss) before income tax	11	7	33	20
Intersegment Elimination [Member]
Operating Revenues
Total Operating Revenues	(111)	(128)	(337)	(375)
Operating expenses
Operating Expenses, Excluding Fuel	(119)	(131)	(353)	(378)
Economic fuel	0	0	0	0
Total Operating Expenses	(119)	(131)	(353)	(378)
Nonoperating Income (Expense)
Interest income	(6)	(4)	(19)	(10)
Interest expense	7	4	20	9
Interest Costs Capitalized	0	0	0	0
Other	0	0	0	0
Nonoperating Income (Expense) Total	1	0	1	(1)
Income (loss) before income tax	9	3	17	2
Special Revenue and Charges [Member]
Operating Revenues
Total Operating Revenues	0	0	0	0
Operating expenses
Operating Expenses, Excluding Fuel	5	22	39	92
Economic fuel	0	5	(1)	(30)
Total Operating Expenses	5	27	38	62
Nonoperating Income (Expense)
Interest income	0	0	0	0
Interest expense	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	(5)	(27)	(38)	(62)
Passenger [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	2,211	2,043	6,038	5,724
Passenger [Member] | Air Group Adjusted [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	2,211	2,043	6,038	5,724
Passenger [Member] | Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	1,850	1,727	5,039	4,879
Passenger [Member] | Alaska Regional [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	361	316	999	845
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	112	128	340	375
Capacity Purchase Agreements [Member] | Intersegment Elimination [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	(112)	(128)	(340)	(375)
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	118	114	346	329
Mileage plan other revenue [Member] | Air Group Adjusted [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	118	114	346	329
Mileage plan other revenue [Member] | Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	107	104	312	301
Mileage plan other revenue [Member] | Alaska Regional [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	11	10	34	28
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	60	55	169	147
Cargo and Freight [Member] | Air Group Adjusted [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	60	55	169	147
Cargo and Freight [Member] | Alaska Mainline [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	58	53	163	142
Cargo and Freight [Member] | Alaska Regional [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	1	0	2	1
Cargo and Freight [Member] | Horizon [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	0	2	1	4
Cargo and Freight [Member] | Intersegment Elimination [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	1	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