Summary Of Accounting Policies And Accounting Changes - Impact on Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Policy Acquisition Costs	$ 303.4	$ 294.0
Current and Deferred Income Tax Assets	5.4	6.4
Total Assets	8,009.1	7,934.7
Liabilities for Income Taxes	21.5	6.2
Total Liabilities	5,847.4	5,818.1
Retained Earnings	1,118.2	1,108.7
Total Shareholders’ Equity	2,161.7	2,116.6	2,023.1	1,834.0
Total Liabilities and Shareholders’ Equity	8,009.1	7,934.7
Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total Shareholders’ Equity				1,917.6
Accounting Standards Update 2010-26 [Member] | Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Policy Acquisition Costs		448.5
Current and Deferred Income Tax Assets		3.1
Total Assets		8,085.9
Liabilities for Income Taxes		57.9
Total Liabilities		5,869.8
Retained Earnings		1,208.2
Total Shareholders’ Equity		2,216.1
Total Liabilities and Shareholders’ Equity		8,085.9
Accounting Standards Update 2010-26 [Member] | Scenario, Computed Without Change in Accounting Principle [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Policy Acquisition Costs	467.7
Total Assets	8,173.4
Liabilities for Income Taxes	80.0
Total Liabilities	5,905.9
Retained Earnings	1,224.0
Total Shareholders’ Equity	2,267.5
Total Liabilities and Shareholders’ Equity	8,173.4
Accounting Standards Update 2010-26 [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Policy Acquisition Costs	(164.3)	(154.5)
Current and Deferred Income Tax Assets		3.3
Total Assets	(164.3)	(151.2)
Liabilities for Income Taxes	(58.5)	(51.7)
Total Liabilities	(58.5)	(51.7)
Retained Earnings	(105.8)	(99.5)
Total Shareholders’ Equity	(105.8)	(99.5)
Total Liabilities and Shareholders’ Equity	$ (164.3)	$ (151.2)