Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 2.1	$ 2.5	$ 1.0
State	0.1	1.0	0.9
International	37.0	29.4	33.3
Current income tax provision	39.2	32.9	35.2
Deferred:
Federal and state	41.8	21.8	(13.2)
International	(0.1)	(0.3)	4.3
Deferred income tax provision	41.7	21.5	(8.9)
Income tax expense	$ 80.9	$ 54.4	$ 26.3