Share-Based Compensation Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based compensation expense
Pre-tax compensation expense	$ 6.0	$ 7.0	$ 13.0	$ 14.0
Income tax benefit	(1.0)	(2.0)	(4.0)	(5.0)
Total share-based compensation expense, net of income taxes	5.0	5.0	9.0	9.0
Employee Stock Option
Share-based compensation expense
Pre-tax compensation expense	2.0	3.0	4.0	5.0
Income tax benefit		(1.0)	(1.0)	(2.0)
Total share-based compensation expense, net of income taxes	2.0	2.0	3.0	3.0
Restricted Stock Units (RSUs)
Share-based compensation expense
Pre-tax compensation expense	3.0	3.0	6.0	6.0
Income tax benefit	(1.0)	(1.0)	(2.0)	(2.0)
Total share-based compensation expense, net of income taxes	2.0	2.0	4.0	4.0
Performance shares and other share-based awards
Share-based compensation expense
Pre-tax compensation expense	1.0	1.0	3.0	3.0
Income tax benefit			(1.0)	(1.0)
Total share-based compensation expense, net of income taxes	$ 1.0	$ 1.0	$ 2.0	$ 2.0