OPERATING SEGMENT INFORMATION, ASSETS (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Total assets	$ 14,262	$ 14,046
Alaska Airlines [Member]
Total assets	19,951	19,754
Horizon [Member]
Total assets	1,200	1,170
Consolidating and Other [Member]
Total assets	$ (6,889)	$ (6,878)