Share-Based Compensation and Capital Stock - Pretax Stock-Based Compensation Expenses And Associated Income Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation expense	$ 9.4	$ 11.5	$ 11.3
Income tax benefits	3.5	4.2	4.1
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation expense	2.4	1.8	2.1
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation expense	7.2	7.5	7.5
Performance Vested Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation expense	$ (0.2)	$ 2.2	$ 1.7