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	3 Months Ended	12 Months Ended
	Mar. 31, 2014 securities	Dec. 31, 2013 securities
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	2,845	3,451
Estimated Fair Value, Less Than 12 Months	$ 5,286.7	$ 6,636.9
Gross Unrealized Loss, Less Than 12 Months	(131.2)	(244.5)
Number of Securities, 12 Months or Greater	277	250
Estimated Fair Value, 12 Months or Greater	449.9	301.7
Gross Unrealized Losses, 12 Months or Greater	(30.6)	(33.3)
Equity Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	505	426
Estimated Fair Value, Less Than 12 Months	131.8	120.8
Gross Unrealized Loss, Less Than 12 Months	(10.6)	(8.0)
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 Maturities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	2,340	3,025
Estimated Fair Value, Less Than 12 Months	5,154.9	6,516.1
Gross Unrealized Loss, Less Than 12 Months	(120.6)	(236.5)
Number of Securities, 12 Months or Greater	277	250
Estimated Fair Value, 12 Months or Greater	449.9	301.7
Gross Unrealized Losses, 12 Months or Greater	(30.6)	(33.3)
Fixed Maturities [Member] | United States Government Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	26	27
Estimated Fair Value, Less Than 12 Months	300.2	179.2
Gross Unrealized Loss, Less Than 12 Months	(1.3)	(3.4)
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 Maturities [Member] | Government Sponsored Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	15	22
Estimated Fair Value, Less Than 12 Months	28.8	73.4
Gross Unrealized Loss, Less Than 12 Months	(0.5)	(1.3)
Number of Securities, 12 Months or Greater	5	0
Estimated Fair Value, 12 Months or Greater	17.0	0
Gross Unrealized Losses, 12 Months or Greater	(0.5)	0
Fixed Maturities [Member] | States, Municipalities And Political Subdivisions, Tax-Exempt [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	496	806
Estimated Fair Value, Less Than 12 Months	1,351.0	2,070.9
Gross Unrealized Loss, Less Than 12 Months	(33.3)	(90.1)
Number of Securities, 12 Months or Greater	73	42
Estimated Fair Value, 12 Months or Greater	168.0	82.4
Gross Unrealized Losses, 12 Months or Greater	(9.5)	(9.6)
Fixed Maturities [Member] | Corporate Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	1,215	1,448
Estimated Fair Value, Less Than 12 Months	2,198.9	2,586.6
Gross Unrealized Loss, Less Than 12 Months	(54.8)	(95.2)
Number of Securities, 12 Months or Greater	102	107
Estimated Fair Value, 12 Months or Greater	127.9	81.3
Gross Unrealized Losses, 12 Months or Greater	(14.1)	(15.5)
Fixed Maturities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	490	605
Estimated Fair Value, Less Than 12 Months	985.9	1,243.0
Gross Unrealized Loss, Less Than 12 Months	(26.8)	(41.4)
Number of Securities, 12 Months or Greater	74	80
Estimated Fair Value, 12 Months or Greater	115.1	116.2
Gross Unrealized Losses, 12 Months or Greater	(5.5)	(7.1)
Fixed Maturities [Member] | Commercial Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	37	52
Estimated Fair Value, Less Than 12 Months	112.4	177.7
Gross Unrealized Loss, Less Than 12 Months	(1.1)	(2.6)
Number of Securities, 12 Months or Greater	4	4
Estimated Fair Value, 12 Months or Greater	4.8	5.6
Gross Unrealized Losses, 12 Months or Greater	(0.2)	(0.3)
Fixed Maturities [Member] | Other Debt Securities [Member]
Schedule of Investments [Line Items]
Number of Securities, Less Than 12 Months	61	65
Estimated Fair Value, Less Than 12 Months	177.7	185.3
Gross Unrealized Loss, Less Than 12 Months	(2.8)	(2.5)
Number of Securities, 12 Months or Greater	19	17
Estimated Fair Value, 12 Months or Greater	17.1	16.2
Gross Unrealized Losses, 12 Months or Greater	$ (0.8)	$ (0.8)