Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2013

Fair Value Disclosures [Abstract]

Assets and liabilities measured at fair value on a recurring basis

Assets and liabilities measured at gross fair value on a recurring basis are summarized below:

	Fair Value Measurements as of December 31, 2013
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	530.6	$	530.6	$	—	$	—
Total assets	$	530.6	$	530.6	$	—	$	—
Total liabilities	$	—	$	—	$	—	$	—

	Fair Value Measurements as of December 31, 2012
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	416.8	$	416.8	$	—	$	—
Jet fuel options	0.3		—		—		0.3
Total assets	$	417.1	$	416.8	$	—	$	0.3
Total liabilities	$	—	$	—	$	—	$	—

Assets and liabilities measured at fair value on a recuring basis using significant unobservable inputs (level 3)

The following table presents the Company’s activity for assets and liabilities measured at gross fair value on a recurring basis using significant unobservable inputs (Level 3):

	Jet Fuel Options
	(in millions)
Balance at January 1, 2011	$	3.5
Total realized or unrealized gains (losses) included in earnings, net	4.2
Settlements, net	(7.4		)
Balance at December 31, 2011	0.3
Total realized or unrealized gains (losses) included in earnings, net	(0.2		)
Settlements, net	0.2
Balance at December 31, 2012	0.3
Total realized or unrealized gains (losses) included in earnings, net	0.1
Settlements, net	(0.4		)
Balance at December 31, 2013	$	—