Changes in Shareholders' Equity Changes in Shareholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jan. 01, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	$ 2,082.4		$ 2,082.4
Net Income			84.0
Other Comprehensive Income	9.8	$ (5.0)	49.4	$ 131.8
Total Comprehensive Income (Loss)	$ 57.5	$ (21.3)	133.4	$ 117.4
Cash Dividends and Dividend Equivalents to Shareholders ($0.72 per share)			(37.1)
Equity-based Compensation Cost			8.7
Equity-based Awards, Net of Shares Exchanged			1.7
Stockholders' Equity Attributable to Parent			$ 1,975.2
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets					$ 0.5