Changes in Shareholders' Equity Changes in Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	$ 2,063.8
Net Income	53.8
Other Comprehensive Income (Loss)	(95.7)	$ 17.1
Total Comprehensive Income (Loss)	(41.9)	$ 16.8
Cash Dividends and Dividend Equivalents to Shareholders ($0.24 per share)	$ (12.5)
Dividends Paid to Shareholders Per Share (in dollars per share)	$ 0.24	$ 0.24
Equity-based Compensation Cost	$ 3.4
Equity-based Awards, Net of Shares Exchanged	(0.8)
Stockholders' Equity Attributable to Parent	$ 2,115.6
AOCI Attributable to Parent [Member] | Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			$ (17.7)
AOCI Attributable to Parent [Member] | Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			35.9
Retained Earnings [Member] | Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			17.7
Retained Earnings [Member] | Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			$ (35.9)