Stock Based Compensation Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock-based Payment Award
Stock-based compensation expense		$ 72.6	$ 56.7	$ 46.0
Tax benefit		26.3	20.6	17.6
Employee Stock Option
Stock-based Payment Award
Stock-based compensation expense		1.0	2.1	3.7
Stock-settled awards
Stock-based Payment Award
Stock-based compensation expense		11.6	10.0	9.8
Cash-settled awards
Stock-based Payment Award
Stock-based compensation expense		0.7	0.6	1.5
Performance-based awards
Stock-based Payment Award
Stock-based compensation expense		57.7	42.2	29.6
Employee stock purchase plan
Stock-based Payment Award
Stock-based compensation expense		0.7	0.6	0.6
Other
Stock-based Payment Award
Stock-based compensation expense	[1]	$ 0.9	$ 1.2	$ 0.8

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