OPERATING SEGMENT INFORMATION (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 1,953	$ 701	$ 4,277	$ 2,758
Operating expenses
Operating Expenses, Excluding Fuel	1,319	1,147	2,778	3,370
Economic fuel	376	125	853	568
Total Operating Expenses	1,695	1,272	3,631	3,938
Nonoperating Income (Expense)
Interest income	6	7	19	23
Interest expense	(30)	(34)	(101)	(64)
Interest capitalized	3	4	9	8
Other—net	8	5	27	16
Nonoperating Income (Expense)	(13)	(18)	(46)	(17)
Costs and Expenses, Total	1,695	1,272	3,631	3,938
Mileage Plan Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	310	148	760	538
Air Group Adjusted [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	1,953	701	4,277	2,758
Operating expenses
Operating Expenses, Excluding Fuel	1,328	1,101	3,699	3,453
Economic fuel	376	128	921	568
Total Operating Expenses	1,704	1,229	4,620	4,021
Nonoperating Income (Expense)
Interest income	6	7	19	23
Interest expense	(30)	(34)	(101)	(64)
Interest capitalized	3	4	9	8
Other—net	8	5	27	16
Nonoperating Income (Expense)	(13)	(18)	(46)	(17)
Income (loss) before income tax	236	(546)	(389)	(1,280)
Alaska Mainline [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	1,588	511	3,447	2,207
Operating expenses
Operating Expenses, Excluding Fuel	1,060	872	2,937	2,777
Economic fuel	299	90	726	448
Total Operating Expenses	1,359	962	3,663	3,225
Nonoperating Income (Expense)
Interest income	7	8	20	33
Interest expense	(25)	(28)	(86)	(58)
Interest capitalized	2	4	8	8
Other—net	8	4	27	16
Nonoperating Income (Expense)	(8)	(12)	(31)	(1)
Income (loss) before income tax	221	(463)	(247)	(1,019)
Alaska Regional [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	364	190	827	549
Operating expenses
Operating Expenses, Excluding Fuel	288	248	839	727
Economic fuel	77	38	195	120
Total Operating Expenses	365	286	1,034	847
Nonoperating Income (Expense)
Interest income	0	0	0	0
Interest expense	0	0	0	0
Interest capitalized	0	0	0	0
Other—net	0	0	0	0
Nonoperating Income (Expense)	0	0	0	0
Income (loss) before income tax	(1)	(96)	(207)	(298)
Horizon [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	107	95	322	281
Operating expenses
Operating Expenses, Excluding Fuel	93	78	272	238
Economic fuel	0	0	0	0
Total Operating Expenses	93	78	272	238
Nonoperating Income (Expense)
Interest income	0	0	0	0
Interest expense	(6)	(6)	(16)	(16)
Interest capitalized	0	0	0	0
Other—net	0	0	0	0
Nonoperating Income (Expense)	(6)	(6)	(16)	(16)
Income (loss) before income tax	8	11	34	27
Consolidating and Other [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	(106)	(95)	(319)	(279)
Operating expenses
Operating Expenses, Excluding Fuel	(113)	(97)	(349)	(289)
Economic fuel	0	0	0	0
Total Operating Expenses	(113)	(97)	(349)	(289)
Nonoperating Income (Expense)
Interest income	(1)	(1)	(1)	(10)
Interest expense	1	0	1	10
Interest capitalized	1	0	1	0
Other—net	0	1	0	0
Nonoperating Income (Expense)	1	0	1	0
Income (loss) before income tax	8	2	31	10
Special Charges [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Operating expenses
Operating Expenses, Excluding Fuel	(9)	46	(921)	(83)
Economic fuel	0	(3)	(68)	0
Total Operating Expenses	(9)	43	(989)	(83)
Nonoperating Income (Expense)
Interest income	0	0	0	0
Interest expense	0	0	0	0
Interest capitalized	0	0	0	0
Other—net	0	0	0	0
Nonoperating Income (Expense)	0	0	0	0
Income (loss) before income tax	9	(43)	989	83
Passenger [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	1,774	572	3,785	2,362
Passenger [Member] | Air Group Adjusted [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	1,774	572	3,785	2,362
Passenger [Member] | Alaska Mainline [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	1,425	401	3,003	1,860
Passenger [Member] | Alaska Regional [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	349	171	782	502
Passenger [Member] | Horizon [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Passenger [Member] | Consolidating and Other [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Passenger [Member] | Special Charges [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Capacity Purchase Agreements [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Capacity Purchase Agreements [Member] | Air Group Adjusted [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Capacity Purchase Agreements [Member] | Alaska Mainline [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Capacity Purchase Agreements [Member] | Alaska Regional [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Capacity Purchase Agreements [Member] | Horizon [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	107	95	322	281
Capacity Purchase Agreements [Member] | Consolidating and Other [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	(107)	(95)	(322)	(281)
Capacity Purchase Agreements [Member] | Special Charges [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Mileage plan other revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	120	84	332	266
Mileage plan other revenue [Member] | Mileage Plan Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	120	84	332	266
Mileage plan other revenue [Member] | Air Group Adjusted [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	120	84	332	266
Mileage plan other revenue [Member] | Alaska Mainline [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	105	65	287	219
Mileage plan other revenue [Member] | Alaska Regional [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	15	19	45	47
Mileage plan other revenue [Member] | Horizon [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Mileage plan other revenue [Member] | Consolidating and Other [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Mileage plan other revenue [Member] | Special Charges [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	59	45	160	130
Cargo and Freight [Member] | Air Group Adjusted [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	59	45	160	130
Cargo and Freight [Member] | Alaska Mainline [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	58	45	157	128
Cargo and Freight [Member] | Alaska Regional [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Cargo and Freight [Member] | Horizon [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Cargo and Freight [Member] | Consolidating and Other [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	1	0	3	2
Cargo and Freight [Member] | Special Charges [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 0	$ 0	$ 0	$ 0