Consolidated Statements of Shareholders’ Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Beginning balance at Dec. 31, 2014	$ 2,090.7	$ 5.2	$ 660.1	$ 1,202.7	$ 222.7
Beginning Balance, shares at Dec. 31, 2014		52.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	85.7			85.7
Other Comprehensive Income (Note 12)	(98.4)				(98.4)
Cash Dividends to Shareholders	(49.7)			(49.7)
Repurchases of Common Stock	$ (43.5)	$ (0.1)	(15.5)	(27.9)
Repurchases of Common Stock, shares	(1.2)	(1.2)
Equity-based Compensation Cost	$ 6.5		6.5
Equity-based Awards, Net of Shares Exchanged	1.1		2.9	(1.8)
Equity-based Awards, Net of Shares Exchanged, shares		0.1
Ending Balance, shares at Dec. 31, 2015		51.3
Ending balance at Dec. 31, 2015	1,992.4	$ 5.1	654.0	1,209.0	124.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	16.8			16.8
Other Comprehensive Income (Note 12)	12.7				12.7
Cash Dividends to Shareholders	(49.2)			(49.2)
Repurchases of Common Stock	$ (3.8)	$ 0.0	(1.8)	(2.0)
Repurchases of Common Stock, shares	(0.1)	(0.1)
Equity-based Compensation Cost	$ 4.7		4.7
Equity-based Awards, Net of Shares Exchanged	1.6		3.4	(1.8)
Equity-based Awards, Net of Shares Exchanged, shares		0.1
Ending Balance, shares at Dec. 31, 2016		51.3
Ending balance at Dec. 31, 2016	1,975.2	$ 5.1	660.3	1,172.8	137.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of Adoption of New Accounting Standard	0.5			0.5
Closing balance, adjusted	1,975.7	$ 5.1	660.3	1,173.3	137.0
Net Income	120.9			120.9
Other Comprehensive Income (Note 12)	57.4				57.4
Cash Dividends to Shareholders	$ (49.5)			(49.5)
Repurchases of Common Stock, shares	0.0
Equity-based Compensation Cost	$ 9.4		9.4
Equity-based Awards, Net of Shares Exchanged	1.7		3.4	(1.7)
Equity-based Awards, Net of Shares Exchanged, shares		0.2
Ending Balance, shares at Dec. 31, 2017		51.5
Ending balance at Dec. 31, 2017	$ 2,115.6	$ 5.1	$ 673.1	$ 1,243.0	$ 194.4