Consolidated Statements of Shareholders’ Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]
Beginning Balance, shares at Dec. 31, 2017		51.5
Beginning balance at Dec. 31, 2017	$ 2,115.6	$ 5.1	$ 673.1	$ 1,243.0	$ 194.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	53.8			53.8
Other Comprehensive Income	(95.7)				(95.7)
Cash Dividends to Shareholders	(12.5)			(12.5)
Equity-based Compensation Cost	3.4		3.4
Equity-based Awards, Net of Shares Exchanged	(0.8)		0.4	(1.2)
Ending Balance, shares at Mar. 31, 2018		51.5
Ending balance at Mar. 31, 2018	2,063.8	$ 5.1	676.9	1,264.9	116.9
Beginning Balance, shares at Dec. 31, 2018		64.7
Beginning balance at Dec. 31, 2018	3,050.1	$ 6.5	1,666.3	1,355.5	21.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	155.3			155.3
Other Comprehensive Income	129.1				129.1
Cash Dividends to Shareholders	(16.4)			(16.4)
Equity-based Compensation Cost	7.6		7.6
Equity-based Awards, Net of Shares Exchanged, shares		0.2
Equity-based Awards, Net of Shares Exchanged	(5.6)		(0.9)	(4.7)
Ending Balance, shares at Mar. 31, 2019		64.9
Ending balance at Mar. 31, 2019	$ 3,320.1	$ 6.5	$ 1,673.0	$ 1,489.7	$ 150.9