Condensed Consolidated Statements of Shareholders’ Equity - USD ($) $ in Millions	Total	Common Stock	Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Previously Reported	Previously Reported Common Stock	Previously Reported Paid-in Capital	Previously Reported Retained Earnings	Previously Reported Accumulated Other Comprehensive Income (Loss)	Cumulative Effect of Adoption of New Accounting Standard	Cumulative Effect of Adoption of New Accounting Standard Retained Earnings	Cumulative Effect of Adoption of New Accounting Standard Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of Adoption of New Accounting Standard											$ 0.5	$ 0.5
Beginning balance (in shares) at Dec. 31, 2016							51,300,000
Beginning balance at Dec. 31, 2016						$ 1,975.2	$ 5.1	$ 660.3	$ 1,172.8	$ 137.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	$ 120.9			$ 120.9
Other Comprehensive Income (Loss) (Note 13)	57.4				$ 57.4
Cash Dividends and Dividend Equivalents to Shareholders	$ (49.5)			(49.5)
Repurchases of Common Stock (in shares)	0
Equity-based Compensation Cost (Note 11)	$ 9.4		$ 9.4
Equity-based Awards, Net of Shares Exchanged (Note 11) (in shares)		200,000
Equity-based Awards, Net of Shares Exchanged (Note 11)	1.7		3.4	(1.7)
Ending balance (in shares) at Dec. 31, 2017		51,500,000					51,500,000
Ending balance at Dec. 31, 2017	2,115.6	$ 5.1	673.1	1,224.8	212.6	$ 2,115.6	$ 5.1	$ 673.1	$ 1,243.0	$ 194.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of Adoption of New Accounting Standard											$ 0.0	$ (18.2)	$ 18.2
Net Income	190.1			190.1
Other Comprehensive Income (Loss) (Note 13)	(190.8)				(190.8)
Cash Dividends and Dividend Equivalents to Shareholders	$ (56.4)			(56.4)
Repurchases of Common Stock (in shares)	0
Equity-based Compensation Cost (Note 11)	$ 18.6		18.6
Equity-based Awards, Net of Shares Exchanged (Note 11) (in shares)		100,000
Equity-based Awards, Net of Shares Exchanged (Note 11)	(5.6)	$ 0.0	(2.6)	(3.0)	0.0
Issuances of Common Stock (in shares)		13,100,000
Issuances of Common Stock	978.6	$ 1.4	977.2	0.0
Ending balance (in shares) at Dec. 31, 2018		64,700,000
Ending 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	531.1			531.1
Other Comprehensive Income (Loss) (Note 13)	314.3				314.3
Cash Dividends and Dividend Equivalents to Shareholders	$ (68.4)			(68.4)
Repurchases of Common Stock (in shares)	0
Equity-based Compensation Cost (Note 11)	$ 25.3		25.3
Equity-based Awards, Net of Shares Exchanged (Note 11) (in shares)		400,000
Equity-based Awards, Net of Shares Exchanged (Note 11)	(9.2)		(1.3)	(7.9)
Issuances of Common Stock (in shares)		1,600,000
Issuances of Common Stock	127.2	$ 0.2	127.0	0.0
Shares Issued Under Employee Stock Purchase Plan (Note 10)	1.9		1.9
Ending balance (in shares) at Dec. 31, 2019		66,700,000
Ending balance at Dec. 31, 2019	$ 3,972.3	$ 6.7	$ 1,819.2	$ 1,810.3	$ 336.1