Stock-Based Compensation (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stock-based compensation expense
Stock-based compensation expense	$ 13.9	$ 12.4	$ 8.3
Tax benefit from stock options exercised during the period	8.5	3.9	3.1
Non-qualified stock options
Stock-based compensation expense
Stock-based compensation expense	4.1	3.9	3.4
RSUs
Stock-based compensation expense
Stock-based compensation expense	5.0	4.9	4.2
PRSUs
Stock-based compensation expense
Stock-based compensation expense	4.7	3.5	0.7
Employee stock purchase plan
Stock-based compensation expense
Stock-based compensation expense	$ 0.1	$ 0.1