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, 2013 securities	Dec. 31, 2012 securities
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	3,675	1,709
Estimated Fair Value, Less Than 12 Months	$ 6,709.4	$ 1,911.2
Gross Unrealized Losses, Less Than 12 Months	(258.5)	(36.7)
Number of Securities, 12 Months or Greater	151	143
Estimated Fair Value, 12 Months or Greater	151.4	158.0
Gross Unrealized Losses, 12 Months or Greater	(18.2)	(14.6)
Fixed Maturity Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	3,051	748
Estimated Fair Value, Less Than 12 Months	6,515.2	1,761.6
Gross Unrealized Losses, Less Than 12 Months	(241.8)	(24.2)
Number of Securities, 12 Months or Greater	151	143
Estimated Fair Value, 12 Months or Greater	151.4	158.0
Gross Unrealized Losses, 12 Months or Greater	(18.2)	(14.6)
Fixed Maturity Securities [Member] | United States Government Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	24	17
Estimated Fair Value, Less Than 12 Months	119.9	48.5
Gross Unrealized Losses, Less Than 12 Months	(1.4)	(0.2)
Number of Securities, 12 Months or Greater	0	0
Estimated Fair Value, 12 Months or Greater	0	0
Gross Unrealized Losses, 12 Months or Greater	0	0
Fixed Maturity Securities [Member] | Government Sponsored Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	23
Estimated Fair Value, Less Than 12 Months	56.6
Gross Unrealized Losses, Less Than 12 Months	(1.5)	0
Number of Securities, 12 Months or Greater	0
Estimated Fair Value, 12 Months or Greater	0
Gross Unrealized Losses, 12 Months or Greater	0	0
Fixed Maturity Securities [Member] | States, Municipalities And Political Subdivisions, Tax-Exempt [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	768	184
Estimated Fair Value, Less Than 12 Months	1,979.3	420.1
Gross Unrealized Losses, Less Than 12 Months	(93.6)	(5.7)
Number of Securities, 12 Months or Greater	22	1
Estimated Fair Value, 12 Months or Greater	14.3	46.9
Gross Unrealized Losses, 12 Months or Greater	(1.2)	(1.6)
Fixed Maturity Securities [Member] | Corporate Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	1,700	457
Estimated Fair Value, Less Than 12 Months	3,075.0	1,066.5
Gross Unrealized Losses, Less Than 12 Months	(109.3)	(17.0)
Number of Securities, 12 Months or Greater	57	74
Estimated Fair Value, 12 Months or Greater	53.0	52.6
Gross Unrealized Losses, 12 Months or Greater	(12.4)	(8.0)
Fixed Maturity Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	434	79
Estimated Fair Value, Less Than 12 Months	921.9	211.0
Gross Unrealized Losses, Less Than 12 Months	(29.4)	(1.1)
Number of Securities, 12 Months or Greater	54	44
Estimated Fair Value, 12 Months or Greater	65.8	25.5
Gross Unrealized Losses, 12 Months or Greater	(3.3)	(1.9)
Fixed Maturity Securities [Member] | Commercial Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	50	4
Estimated Fair Value, Less Than 12 Months	216.8	10.1
Gross Unrealized Losses, Less Than 12 Months	(3.4)	0
Number of Securities, 12 Months or Greater	1	3
Estimated Fair Value, 12 Months or Greater	0.6	4.1
Gross Unrealized Losses, 12 Months or Greater	0	0
Fixed Maturity Securities [Member] | Other Debt Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	52	7
Estimated Fair Value, Less Than 12 Months	145.7	5.4
Gross Unrealized Losses, Less Than 12 Months	(3.2)	(0.2)
Number of Securities, 12 Months or Greater	17	21
Estimated Fair Value, 12 Months or Greater	17.7	28.9
Gross Unrealized Losses, 12 Months or Greater	(1.3)	(3.1)
Equity Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	624	961
Estimated Fair Value, Less Than 12 Months	194.2	149.6
Gross Unrealized Losses, Less Than 12 Months	(16.7)	(12.5)
Number of Securities, 12 Months or Greater	0	0
Estimated Fair Value, 12 Months or Greater	0	0
Gross Unrealized Losses, 12 Months or Greater	$ 0	$ 0