Stock-Based Compensation - Schedule of Other Stock Option Statistics (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Other disclosures
Total unrecognized compensation cost on nonvested options	$ 3.9
Non-qualified stock options
Other disclosures
Aggregate intrinsic value of outstanding options	63.6	82.5
Aggregate intrinsic value of exercisable options	59.5	66.9
Total intrinsic value of options exercised	9.7	10.9
Total number of options exercisable (in shares)	2.3	2.2
Weighted average exercise price of options exercisable (in dollars per share)	$ 16.16	$ 14.09
Total unrecognized compensation cost on nonvested options	$ 1.1	$ 1.6