FAIR VALUE MEASUREMENTS (TABLES)

6 Months Ended

Jun. 30, 2012

Fair Value Disclosures [Abstract]

Fair Value, Measurement Inputs, Disclosure [Table Text Block]

Fair values of financial instruments on the consolidated balance sheet (in millions):

June 30, 2012	Level 1		Level 2			Total
Assets
Marketable securities
U.S. government and agency securities	$	368.8	$	—		$	368.8
Foreign government bonds	—		42.3			42.3
Asset-back securities	—		90.7			90.7
Mortgage-back securities	—		110.4			110.4
Corporate notes and bonds	—		522.8			522.8
Municipal securities	—		15.0			15.0
Derivative instruments
Fuel hedge contracts	—		61.3			61.3
Liabilities
Derivative instruments
Interest rate swap agreements	—		(32.0		)	(32.0		)

December 31, 2011	Level 1		Level 2			Total
Assets
Marketable securities
U.S. government and agency securities	$	295.9	$	—		$	295.9
Foreign government bonds	—		25.4			25.4
Asset-back securities	—		58.0			58.0
Mortgage-back securities	—		124.9			124.9
Corporate notes and bonds	—		522.6			522.6
Municipal securities	—		11.9			11.9
Derivative instruments
Fuel hedge contracts	—		116.9			116.9
Liabilities
Derivative instruments
Fuel hedge contracts	—		(10.3		)	(10.3		)
Interest rate swap agreements	—		(28.8		)	(28.8		)

Fair Value, by Balance Sheet Grouping [Table Text Block]

Fixed-rate debt that is not carried at fair value on the consolidated balance sheet and the estimated fair value of long-term fixed-rate debt (in millions):

	June 30, 2012		December 31, 2011
Carrying amount	$	933.3	$	1,002.5
Fair value	1,016.3		1,075.8