OPERATING SEGMENT INFORMATION, ASSETS (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Total assets	$ 5,436.1		$ 5,195.0
Alaska Airlines [Member]
Total assets	5,082.0	[1]	4,803.3	[1]
Horizon [Member]
Total assets	850.8		846.5
Parent [Member]
Total assets	1,770.2		1,583.5
Intersegment Elimination [Member]
Total assets	$ (2,266.9)		$ (2,038.3)

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