Investments (Aggregate Fair Value And Gross Unrealized Loss Of Fixed Maturity Securities And Equity Securities In An Unrealized Loss Position) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Investments [Line Items]
Number of Securities, 12 Months or Less	1,356	2,352
Estimated Fair Value, 12 Months or Less	$ 1,022.8	$ 2,480.0
Gross Unrealized Losses, Less than 12 Months	(30.5)	(129.2)
Number of Securities, Greater than 12 Months	197	221
Estimated Fair Value, Greater than 12 Months	259.0	356.9
Gross Unrealized Losses, Greater than 12 Months	(21.8)	(41.6)
Fixed Maturity Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, 12 Months or Less	386	1,215
Estimated Fair Value, 12 Months or Less	929.4	2,208.4
Gross Unrealized Losses, Less than 12 Months	(14.2)	(103.0)
Number of Securities, Greater than 12 Months	197	221
Estimated Fair Value, Greater than 12 Months	259.0	356.9
Gross Unrealized Losses, Greater than 12 Months	(21.8)	(41.6)
Fixed Maturity Securities [Member] | States, Municipalities And Political Subdivisions - Tax-Exempt [Member]
Schedule of Investments [Line Items]
Number of Securities, 12 Months or Less	27	19
Estimated Fair Value, 12 Months or Less	81.0	86.6
Gross Unrealized Losses, Less than 12 Months	(0.6)	(3.9)
Number of Securities, Greater than 12 Months	32	84
Estimated Fair Value, Greater than 12 Months	76.5	195.2
Gross Unrealized Losses, Greater than 12 Months	(2.2)	(15.0)
Fixed Maturity Securities [Member] | Corporate Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, 12 Months or Less	317	1,047
Estimated Fair Value, 12 Months or Less	794.0	1,798.1
Gross Unrealized Losses, Less than 12 Months	(13.1)	(88.4)
Number of Securities, Greater than 12 Months	100	36
Estimated Fair Value, Greater than 12 Months	116.8	35.4
Gross Unrealized Losses, Greater than 12 Months	(13.1)	(6.9)
Fixed Maturity Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, 12 Months or Less	28	91
Estimated Fair Value, 12 Months or Less	40.0	170.4
Gross Unrealized Losses, Less than 12 Months	(0.2)	(7.6)
Number of Securities, Greater than 12 Months	39	65
Estimated Fair Value, Greater than 12 Months	30.9	78.0
Gross Unrealized Losses, Greater than 12 Months	(2.8)	(10.9)
Fixed Maturity Securities [Member] | Commercial Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, 12 Months or Less	6	14
Estimated Fair Value, 12 Months or Less	6.4	27.7
Gross Unrealized Losses, Less than 12 Months	(0.1)	(1.0)
Number of Securities, Greater than 12 Months	3	5
Estimated Fair Value, Greater than 12 Months	4.1	15.6
Gross Unrealized Losses, Greater than 12 Months	(0.1)	(1.7)
Fixed Maturity Securities [Member] | Other Debt Obligations [Member]
Schedule of Investments [Line Items]
Number of Securities, 12 Months or Less	8	41
Estimated Fair Value, 12 Months or Less	8.0	118.5
Gross Unrealized Losses, Less than 12 Months	(0.2)	(2.0)
Number of Securities, Greater than 12 Months	23	31
Estimated Fair Value, Greater than 12 Months	30.7	32.7
Gross Unrealized Losses, Greater than 12 Months	(3.6)	(7.1)
Fixed Maturity Securities [Member] | United States Government Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, 12 Months or Less	0	3
Estimated Fair Value, 12 Months or Less	0	7.1
Gross Unrealized Losses, Less than 12 Months	0	(0.1)
Number of Securities, Greater than 12 Months	0	0
Estimated Fair Value, Greater than 12 Months	0	0
Gross Unrealized Losses, Greater than 12 Months	0	0
Fixed Maturity Securities [Member] | Government Sponsored Securities [Member]
Schedule of Investments [Line Items]
Gross Unrealized Losses, Less than 12 Months	0	0
Gross Unrealized Losses, Greater than 12 Months	0	0
Equity Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, 12 Months or Less	970	1,137
Estimated Fair Value, 12 Months or Less	93.4	271.6
Gross Unrealized Losses, Less than 12 Months	(16.3)	(26.2)
Number of Securities, Greater than 12 Months	0	0
Estimated Fair Value, Greater than 12 Months	0	0
Gross Unrealized Losses, Greater than 12 Months	$ 0	$ 0