OPERATING SEGMENT INFORMATION (DETAILS) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Operating revenues
Passenger, Mainline	$ 862.7		$ 774.2		$ 1,586.1		$ 1,433.5
Passenger, Regional	187.6		179.0		360.4		340.6
Total passenger revenue	1,050.3		953.2		1,946.5		1,774.1
Segment Reporting Information, Intersegment Revenue	0		0		0		0
Freight and mail	30.6		29.1		55.0		54.0
Other - net	132.3		127.9		251.0		247.3
Total Operating Revenues	1,213.2		1,110.2		2,252.5		2,075.4
Operating expenses
Operating expenses, excluding fuel	665.6		654.9		1,313.7		1,291.8
Economic fuel	431.8		397.5		750.6		592.0
Total Operating Expenses	1,097.4		1,052.4		2,064.3		1,883.8
Nonoperating income (expense)
Interest income	5.1		6.3		10.0		13.9
Interest expense	(17.2)		(20.0)		(33.8)		(43.4)
Other	5.4		2.9		11.3		5.6
Nonoperating Income (Expense) Total	(6.7)		(10.8)		(12.5)		(23.9)
Income (loss) before income tax	109.1		47.0		175.7		167.7
Air Group Adjusted [Member]
Operating revenues
Passenger, Mainline	862.7	[1]	774.2	[1]	1,586.1	[1]	1,433.5	[1]
Passenger, Regional	187.6	[1]	179.0	[1]	360.4	[1]	340.6	[1]
Total passenger revenue	1,050.3	[1]	953.2	[1]	1,946.5	[1]	1,774.1	[1]
Segment Reporting Information, Intersegment Revenue	0		0		0		0
Freight and mail	30.6	[1]	29.1	[1]	55.0	[1]	54.0	[1]
Other - net	132.3	[1]	127.9	[1]	251.0	[1]	247.3	[1]
Total Operating Revenues	1,213.2	[1]	1,110.2	[1]	2,252.5	[1]	2,075.4	[1]
Operating expenses
Operating expenses, excluding fuel	665.6	[1]	628.1	[1]	1,313.7	[1]	1,254.9	[1]
Economic fuel	362.2	[1]	326.6	[1]	700.9	[1]	603.1	[1]
Total Operating Expenses	1,027.8	[1]	954.7	[1]	2,014.6	[1]	1,858.0	[1]
Nonoperating income (expense)
Interest income	5.1	[1]	6.3	[1]	10.0	[1]	13.9	[1]
Interest expense	(17.2)	[1]	(20.0)	[1]	(33.8)	[1]	(43.4)	[1]
Other	5.4	[1]	2.9	[1]	11.3	[1]	5.6	[1]
Nonoperating Income (Expense) Total	(6.7)	[1]	(10.8)	[1]	(12.5)	[1]	(23.9)	[1]
Income (loss) before income tax	178.7	[1]	144.7	[1]	225.4	[1]	193.5	[1]
Alaska Mainline [Member]
Operating revenues
Passenger, Mainline	862.7		774.2		1,586.1		1,433.5
Passenger, Regional	0		0		0		0
Total passenger revenue	862.7		774.2		1,586.1		1,433.5
Segment Reporting Information, Intersegment Revenue	0		0		0		0
Freight and mail	29.5		28.0		53.0		51.9
Other - net	115.4		110.7		218.2		212.7
Total Operating Revenues	1,007.6		912.9		1,857.3		1,698.1
Operating expenses
Operating expenses, excluding fuel	532.2		498.4		1,051.8		996.1
Economic fuel	316.7		285.2		611.1		523.6
Total Operating Expenses	848.9		783.6		1,662.9		1,519.7
Nonoperating income (expense)
Interest income	4.4		7.1		9.3		15.8
Interest expense	(12.7)		(16.3)		(25.3)		(36.0)
Other	5.1		2.3		10.4		4.4
Nonoperating Income (Expense) Total	(3.2)		(6.9)		(5.6)		(15.8)
Income (loss) before income tax	155.5		122.4		188.8		162.6
Alaska Regional [Member]
Operating revenues
Passenger, Mainline	0		0		0		0
Passenger, Regional	187.6		179.0		360.4		340.6
Total passenger revenue	187.6		179.0		360.4		340.6
Segment Reporting Information, Intersegment Revenue	0		0		0		0
Freight and mail	1.1		1.0		2.0		2.0
Other - net	15.1		15.4		29.1		30.4
Total Operating Revenues	203.8		195.4		391.5		373.0
Operating expenses
Operating expenses, excluding fuel	139.0		138.1		275.8		271.0
Economic fuel	45.5		41.4		89.8		79.5
Total Operating Expenses	184.5		179.5		365.6		350.5
Nonoperating income (expense)
Interest income	0		0		0		0
Interest expense	0		0		0		0
Other	0		0		0		0
Nonoperating Income (Expense) Total	0		0		0		0
Income (loss) before income tax	19.3		15.9		25.9		22.5
Horizon [Member]
Operating revenues
Passenger, Mainline	0		0		0		0
Passenger, Regional	0		0		0		0
Total passenger revenue	0		0		0		0
Segment Reporting Information, Intersegment Revenue	89.2		93.5		176.2		188.1
Freight and mail	0		0.1		0		0.1
Other - net	1.8		1.8		3.7		4.2
Total Operating Revenues	91.0		95.4		179.9		192.4
Operating expenses
Operating expenses, excluding fuel	83.1		83.8		161.4		174.0
Economic fuel	0		0		0		0
Total Operating Expenses	83.1		83.8		161.4		174.0
Nonoperating income (expense)
Interest income	0		0		0		0
Interest expense	(4.1)		(4.4)		(8.1)		(9.1)
Other	0.4		0.2		0.8		1.0
Nonoperating Income (Expense) Total	(3.7)		(4.2)		(7.3)		(8.1)
Income (loss) before income tax	4.2		7.4		11.2		10.3
Intersegment Elimination [Member]
Operating revenues
Passenger, Mainline	0		0		0		0
Passenger, Regional	0		0		0		0
Total passenger revenue	0		0		0		0
Segment Reporting Information, Intersegment Revenue	(89.2)		(93.5)		(176.2)		(188.1)
Freight and mail	0		0		0		0
Other - net	0		0		0		0
Total Operating Revenues	(89.2)		(93.5)		(176.2)		(188.1)
Operating expenses
Operating expenses, excluding fuel	(88.7)		(92.2)		(175.3)		(186.2)
Economic fuel	0		0		0		0
Total Operating Expenses	(88.7)		(92.2)		(175.3)		(186.2)
Nonoperating income (expense)
Interest income	0.7		(0.8)		0.7		(1.9)
Interest expense	(0.4)		0.7		(0.4)		1.7
Other	(0.1)		0.4		0.1		0.2
Nonoperating Income (Expense) Total	0.2		0.3		0.4		0
Income (loss) before income tax	(0.3)		(1.0)		(0.5)		(1.9)
Special Charges [Member]
Operating revenues
Passenger, Mainline	0		0		0		0
Passenger, Regional	0		0		0		0
Total passenger revenue	0		0		0		0
Segment Reporting Information, Intersegment Revenue	0		0		0		0
Freight and mail	0		0		0		0
Other - net	0		0		0		0
Total Operating Revenues	0		0		0		0
Operating expenses
Operating expenses, excluding fuel	0		26.8	[2]	0		36.9	[2]
Economic fuel	69.6	[3]	70.9	[3]	49.7	[3]	(11.1)	[3]
Total Operating Expenses	69.6		97.7		49.7		25.8
Nonoperating income (expense)
Interest income	0		0		0		0
Interest expense	0		0		0		0
Other	0		0		0		0
Nonoperating Income (Expense) Total	0		0		0		0
Income (loss) before income tax	$ (69.6)		$ (97.7)		$ (49.7)		$ (25.8)

[1] The adjusted column represents the financial information that is reviewed by management to assess performance of operations and determine capital allocations and does not include certain charges.

[2] Refer to Note 12 for a summary of special charges.

[3] Represents adjustments to reflect the timing of gain or loss recognition resulting from mark-to-market fuel-hedge accounting.