Stock Based Compensation Expense (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Stock-based Payment Award
Stock-based compensation expense	$ 56.7		$ 46.0		$ 50.4
Tax benefit	20.6		17.6		19.7
Employee Stock Option
Stock-based Payment Award
Stock-based compensation expense	2.1		3.7		5.4
Stock-settled awards
Stock-based Payment Award
Stock-based compensation expense	10.0		9.8		14.9
Cash-settled awards
Stock-based Payment Award
Stock-based compensation expense	0.6		1.5		3.9
Performance-based awards
Stock-based Payment Award
Stock-based compensation expense	42.2		29.6		24.5
Employee stock purchase plan
Stock-based Payment Award
Stock-based compensation expense	0.6		0.6		0.6
Other
Stock-based Payment Award
Stock-based compensation expense	$ 1.2	[1]	$ 0.8	[1]	$ 1.1	[1]

[1] Represents charges recorded for severance expense related to stock-based compensation awards.