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, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation expense	$ 15.0	$ 24.9	$ 14.6
Income tax benefits	3.6	9.2	5.4
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation expense	2.4	9.2	4.6
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation expense	6.8	9.0	7.5
Performance Vested Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation expense	$ 5.8	$ 6.7	$ 2.5