Consolidated Statements of Shareholders’ Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income
Beginning balance (in shares) at Dec. 31, 2019		66.7
Beginning balance at Dec. 31, 2019	$ 3,972.3	$ 6.7	$ 1,819.2	$ 1,810.3	$ 336.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	312.4			312.4
Other Comprehensive Income (Loss), Net of Tax	212.9				212.9
Cash Dividends and Dividend Equivalents to Shareholders	(59.6)			(59.6)
Repurchases of Common Stock (in shares)		1.6
Repurchases of Common Stock (Note 10)	(110.4)	$ (0.2)	(44.2)	(66.0)
Shares Issued Under Employee Stock Purchase Plan			3.1
Shares Issued Under Employee Stock Purchase Plan	3.1
Equity-based Compensation Cost	19.7		19.7
Equity-based Awards, Net of Shares Exchanged (in shares)		0.3
Equity-based Awards, Net of Shares Exchanged	(2.9)	$ 0.0	0.7	(3.6)
Ending balance (in shares) at Sep. 30, 2020		65.4
Ending balance at Sep. 30, 2020	4,347.5	$ 6.5	1,798.5	1,993.5	549.0
Beginning balance (in shares) at Jun. 30, 2020		65.3
Beginning balance at Jun. 30, 2020	4,187.9	$ 6.5	1,792.5	1,891.6	497.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	122.3			122.3
Other Comprehensive Income (Loss), Net of Tax	51.7				51.7
Cash Dividends and Dividend Equivalents to Shareholders	(19.7)			(19.7)
Shares Issued Under Employee Stock Purchase Plan	1.2		1.2
Equity-based Compensation Cost	6.1		6.1
Equity-based Awards, Net of Shares Exchanged (in shares)		0.1
Equity-based Awards, Net of Shares Exchanged	(2.0)	$ 0.0	(1.3)	(0.7)
Ending balance (in shares) at Sep. 30, 2020		65.4
Ending balance at Sep. 30, 2020	4,347.5	$ 6.5	1,798.5	1,993.5	549.0
Beginning balance (in shares) at Dec. 31, 2020		65.4
Beginning balance at Dec. 31, 2020	4,563.4	$ 6.5	1,805.2	2,071.2	680.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	(14.7)			(14.7)
Other Comprehensive Income (Loss), Net of Tax	(201.1)				(201.1)
Cash Dividends and Dividend Equivalents to Shareholders	(61.1)			(61.1)
Repurchases of Common Stock (in shares)		2.1
Repurchases of Common Stock (Note 10)	(161.7)	$ (0.2)	(57.8)	(103.7)
Shares Issued Under Employee Stock Purchase Plan	3.9	$ 0.1	3.9
Equity-based Compensation Cost	24.6		24.6
Equity-based Awards, Net of Shares Exchanged (in shares)		0.3
Equity-based Awards, Net of Shares Exchanged	(2.1)	$ 0.1	1.1	(3.3)
Ending balance (in shares) at Sep. 30, 2021		63.7
Ending balance at Sep. 30, 2021	4,151.2	$ 6.4	1,777.0	1,888.4	479.4
Beginning balance (in shares) at Jun. 30, 2021		63.6
Beginning balance at Jun. 30, 2021	4,306.2	$ 6.4	1,770.9	1,985.9	543.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	(75.3)			(75.3)
Other Comprehensive Income (Loss), Net of Tax	(63.6)				(63.6)
Cash Dividends and Dividend Equivalents to Shareholders	(19.7)			(19.7)
Repurchases of Common Stock (in shares)		0.1
Repurchases of Common Stock (Note 10)	(3.0)	$ 0.0	(1.1)	(1.9)
Shares Issued Under Employee Stock Purchase Plan	1.4	$ 0.1	1.4
Equity-based Compensation Cost	6.1		6.1
Equity-based Awards, Net of Shares Exchanged (in shares)		0.1
Equity-based Awards, Net of Shares Exchanged	(0.9)	$ 0.0	(0.3)	(0.6)
Ending balance (in shares) at Sep. 30, 2021		63.7
Ending balance at Sep. 30, 2021	$ 4,151.2	$ 6.4	$ 1,777.0	$ 1,888.4	$ 479.4