Stock-Based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense, Before Tax	$ 21.9	$ 23.8	$ 22.6
Allocated Share-based Compensation Expense, Net of Tax	14.4	15.7	14.9
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense, Before Tax	6.6	4.5	2.5
Restricted Stock Units and Cash-Settled Awards
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense, Before Tax	14.9	18.6	19.0
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense, Before Tax	0.0	0.2	0.6
Other Awards
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense, Before Tax	$ 0.4	$ 0.5	$ 0.5