Stock-Based Compensation - Schedule of Stock-Based Compensation Expense by Type of Award (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 17.2	$ 18.9	$ 15.8
Tax benefit from stock options exercised during the period	5.8	5.3	6.8
Non-qualified stock options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	3.6	3.8	4.5
RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	6.0	6.0	6.5
PRSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	7.4	8.8	4.6
Employee stock purchase plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 0.2	$ 0.3	$ 0.2