OPERATING SEGMENT INFORMATION, ASSETS (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Total assets	$ 5,382.0		$ 5,195.0
Alaska Airlines [Member]
Total assets	4,894.2	[1]	4,803.3	[1]
Horizon [Member]
Total assets	851.4		846.5
Parent [Member]
Total assets	1,506.5		1,583.5
Intersegment Elimination [Member]
Total assets	$ (1,870.1)		$ (2,038.3)

[1] There are no assets associated with purchased capacity flying at Alaska.