OPERATING SEGMENT INFORMATION (DETAILS) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Operating revenues
Passenger, Mainline	$ 904.6		$ 835.6		$ 2,490.7		$ 2,269.1
Passenger, Regional	198.1		196.1		558.5		536.7
Total passenger revenue	1,102.7		1,031.7		3,049.2		2,805.8
Segment Reporting Information, Intersegment Revenue	0		0		0		0
Freight and mail	29.6		29.9		84.6		83.9
Other - net	139.9		136.5		390.9		383.8
Total Operating Revenues	1,272.2		1,198.1		3,524.7		3,273.5
Operating expenses
Operating expenses, excluding fuel	666.1		634.8		1,979.8		1,926.6
Economic fuel	336.6		420.1		1,087.2		1,012.1
Total Operating Expenses	1,002.7		1,054.9		3,067.0		2,938.7
Nonoperating income (expense)
Interest income	4.5		4.5		14.5		18.4
Interest expense	(15.1)		(25.7)		(48.9)		(69.1)
Other	6.7		3.3		18.0		8.9
Nonoperating Income (Expense) Total	(3.9)		(17.9)		(16.4)		(41.8)
Income (loss) before income tax	265.6		125.3		441.3		293.0
Air Group Adjusted [Member]
Operating revenues
Passenger, Mainline	904.6	[1]	835.6	[1]	2,490.7	[1]	2,269.1	[1]
Passenger, Regional	198.1	[1]	196.1	[1]	558.5	[1]	536.7	[1]
Total passenger revenue	1,102.7	[1]	1,031.7	[1]	3,049.2	[1]	2,805.8	[1]
Segment Reporting Information, Intersegment Revenue	0		0		0		0
Freight and mail	29.6	[1]	29.9	[1]	84.6	[1]	83.9	[1]
Other - net	139.9	[1]	136.5	[1]	390.9	[1]	383.8	[1]
Total Operating Revenues	1,272.2	[1]	1,198.1	[1]	3,524.7	[1]	3,273.5	[1]
Operating expenses
Operating expenses, excluding fuel	666.1	[1]	632.8	[1]	1,979.8	[1]	1,887.7	[1]
Economic fuel	357.8	[1]	335.8	[1]	1,058.7	[1]	938.9	[1]
Total Operating Expenses	1,023.9	[1]	968.6	[1]	3,038.5	[1]	2,826.6	[1]
Nonoperating income (expense)
Interest income	4.5	[1]	4.5	[1]	14.5	[1]	18.4	[1]
Interest expense	(15.1)	[1]	(25.7)	[1]	(48.9)	[1]	(69.1)	[1]
Other	6.7	[1]	3.3	[1]	18.0	[1]	8.9	[1]
Nonoperating Income (Expense) Total	(3.9)	[1]	(17.9)	[1]	(16.4)	[1]	(41.8)	[1]
Income (loss) before income tax	244.4	[1]	211.6	[1]	469.8	[1]	405.1	[1]
Alaska Mainline [Member]
Operating revenues
Passenger, Mainline	904.6		835.6		2,490.7		2,269.1
Passenger, Regional	0		0		0		0
Total passenger revenue	904.6		835.6		2,490.7		2,269.1
Segment Reporting Information, Intersegment Revenue	0		0		0		0
Freight and mail	28.4		28.8		81.4		80.7
Other - net	121.5		117.0		339.7		329.7
Total Operating Revenues	1,054.5		981.4		2,911.8		2,679.5
Operating expenses
Operating expenses, excluding fuel	531.7		504.1		1,583.5		1,500.2
Economic fuel	312.0		292.4		923.1		816.0
Total Operating Expenses	843.7		796.5		2,506.6		2,316.2
Nonoperating income (expense)
Interest income	4.7		4.6		14.0		20.4
Interest expense	(11.3)		(21.8)		(36.6)		(57.8)
Other	6.5		3.4		16.9		8.0
Nonoperating Income (Expense) Total	(0.1)		(13.8)		(5.7)		(29.4)
Income (loss) before income tax	210.7		171.1		399.5		333.9
Alaska Regional [Member]
Operating revenues
Passenger, Mainline	0		0		0		0
Passenger, Regional	198.1		196.1		558.5		536.7
Total passenger revenue	198.1		196.1		558.5		536.7
Segment Reporting Information, Intersegment Revenue	0		0		0		0
Freight and mail	1.1		1.1		3.1		3.0
Other - net	16.7		17.5		45.8		48.0
Total Operating Revenues	215.9		214.7		607.4		587.7
Operating expenses
Operating expenses, excluding fuel	144.9		136.5		420.7		408.0
Economic fuel	45.8		43.4		135.6		122.9
Total Operating Expenses	190.7		179.9		556.3		530.9
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	25.2		34.8		51.1		56.8
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	96.1		91.2		272.3		279.3
Freight and mail	0.1		0		0.1		0.2
Other - net	1.7		2.0		5.4		6.1
Total Operating Revenues	97.9		93.2		277.8		285.6
Operating expenses
Operating expenses, excluding fuel	86.2		82.9		247.6		256.9
Economic fuel	0		0		0		0
Total Operating Expenses	86.2		82.9		247.6		256.9
Nonoperating income (expense)
Interest income	0		0		0		0
Interest expense	(4.0)		(4.0)		(12.1)		(13.1)
Other	0.3		0.1		1.1		1.0
Nonoperating Income (Expense) Total	(3.7)		(3.9)		(11.0)		(12.1)
Income (loss) before income tax	8.0		6.4		19.2		16.6
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	(96.1)		(91.2)		(272.3)		(279.3)
Freight and mail	0		0		0		0
Other - net	0		0		0		0
Total Operating Revenues	(96.1)		(91.2)		(272.3)		(279.3)
Operating expenses
Operating expenses, excluding fuel	(96.7)		(90.7)		(272.0)		(277.4)
Economic fuel	0		0		0		0
Total Operating Expenses	(96.7)		(90.7)		(272.0)		(277.4)
Nonoperating income (expense)
Interest income	(0.2)		(0.1)		0.5		(2.0)
Interest expense	0.2		0.1		(0.2)		1.8
Other	(0.1)		(0.2)		0		(0.1)
Nonoperating Income (Expense) Total	(0.1)		(0.2)		0.3		(0.3)
Income (loss) before income tax	0.5		(0.7)		0		(2.2)
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		2.0	[2]	0		38.9	[2]
Economic fuel	(21.2)	[3]	84.3	[3]	28.5	[3]	73.2	[3]
Total Operating Expenses	(21.2)		86.3		28.5		112.1
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	$ 21.2		$ (86.3)		$ (28.5)		$ (112.1)

[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.