Share-Based Compensation and Capital Stock - Pretax Stock-Based Compensation Expenses And Associated Income Tax Benefits (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 [Line Items]
Pretax stock-based compensation expense	$ 14.6	$ 12.1	$ 9.4
Income tax benefits	5.4	4.5	3.5
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation expense	4.6	3.4	2.4
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation expense	7.5	6.8	7.2
Performance Vested Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation expense	$ 2.5	$ 1.9	$ (0.2)