Share-Based Compensation (Expense Related to Non-vested Stock Awards) (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, Compensation Cost [Line Items]
Total pre-tax share-based compensation expense	$ 5.4	$ 12.1	$ 15.8
Excess tax benefit (deficiency) on share-based compensation	(5.0)	(1.7)	(0.5)
Non-Qualified Stock Option Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total pre-tax share-based compensation expense	0.6	1.5	2.3
Immediately Vested Stock Awards Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total pre-tax share-based compensation expense	0.0	0.0	0.8
Stock Unit Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total pre-tax share-based compensation expense	3.4	4.5	8.0
Performance-Based Non-Vested Stock Awards Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total pre-tax share-based compensation expense	$ 1.4	$ 6.1	$ 4.7