Consolidated Statements of Shareholders’ Equity (USD $) In Millions, unless otherwise specified	Total	Common Stock [Member]	Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Balance at Dec. 31, 2009 (Scenario, Previously Reported [Member])	$ 1,917.6	$ 6.2	$ 765.9	$ 1,086.7	$ 58.8
Balance at Dec. 31, 2009	1,834.0	6.2	765.9	1,003.1	58.8
Balance, shares at Dec. 31, 2009 (Scenario, Previously Reported [Member])		62.4
Balance, shares at Dec. 31, 2009		62.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	177.9			177.9
Net Income (Scenario, Previously Reported [Member]) (Accounting Standards Update 2010-26 [Member])	184.6
Other Comprehensive Income	98.6				98.6
Cash Dividends to Shareholders	(54.6)			(54.6)
Repurchases of Common Stock	(34.4)	(0.1)	(17.0)	(17.3)
Repurchases of Common Stock, shares	(1.4)	(1.4)
Equity-based Compensation Cost (note 10)	4.2		4.2
Equity-based Awards, Net of Shares Exchanged (note 10)	(2.6)		(2.0)	(0.6)
Equity-based Awards, Net of Shares Exchanged, shares (note 10)		0.1
Balance at Dec. 31, 2010	2,023.1	6.1	751.1	1,108.5	157.4
Balance, shares at Dec. 31, 2010		61.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	74.5			74.5
Net Income (Scenario, Previously Reported [Member]) (Accounting Standards Update 2010-26 [Member])	83.7
Other Comprehensive Income	100.6				100.6
Cash Dividends to Shareholders	(58.2)			(58.2)
Repurchases of Common Stock	(27.4)	(0.1)	(11.6)	(15.7)
Repurchases of Common Stock, shares	(0.9)	(0.9)
Equity-based Compensation Cost (note 10)	5.3		5.3
Equity-based Awards, Net of Shares Exchanged (note 10)	(1.3)		(0.9)	(0.4)
Equity-based Awards, Net of Shares Exchanged, shares (note 10)		0.1
Balance (Scenario, Previously Reported [Member]) (Accounting Standards Update 2010-26 [Member])	2,216.1
Balance at Dec. 31, 2011	2,116.6	6.0	743.9	1,108.7	258.0
Balance, shares at Dec. 31, 2011		60.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	103.4			103.4
Other Comprehensive Income	54.7				54.7
Cash Dividends to Shareholders	(56.9)			(56.9)
Repurchases of Common Stock	(60.7)	(0.2)	(24.9)	(35.6)
Repurchases of Common Stock, shares	2.0	(2.0)
Equity-based Compensation Cost (note 10)	5.8		5.8
Equity-based Awards, Net of Shares Exchanged (note 10)	(1.2)		0.2	(1.4)
Equity-based Awards, Net of Shares Exchanged, shares (note 10)		0.2
Balance at Dec. 31, 2012	$ 2,161.7	$ 5.8	$ 725.0	$ 1,118.2	$ 312.7
Balance, shares at Dec. 31, 2012		58.5