Investments (Aggregate Fair Value And Gross Unrealized Loss Of Fixed Maturity Securities And Equity Securities In An Unrealized Loss Position) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) securities	Dec. 31, 2014 USD ($) securities
Investment [Line Items]
Number of Securities, Less than 12 Months | securities	4,060	2,564
Estimated Fair Value, Less than 12 Months	$ 7,327.4	$ 4,381.7
Gross Unrealized Losses, Less than 12 Months	$ (321.5)	$ (139.6)
Number of Securities, 12 Months or Greater | securities	587	629
Estimated Fair Value, 12 Months or Greater	$ 840.9	$ 1,215.6
Gross Unrealized Losses, 12 Months or Greater	$ (126.0)	$ (57.2)
Fixed Maturity Securities [Member]
Investment [Line Items]
Number of Securities, Less than 12 Months | securities	3,268	2,157
Estimated Fair Value, Less than 12 Months	$ 7,066.3	$ 4,256.3
Gross Unrealized Losses, Less than 12 Months	$ (290.6)	$ (128.5)
Number of Securities, 12 Months or Greater | securities	587	629
Estimated Fair Value, 12 Months or Greater	$ 840.9	$ 1,215.6
Gross Unrealized Losses, 12 Months or Greater	$ (126.0)	$ (57.2)
Fixed Maturity Securities [Member] | United States Government Securities [Member]
Investment [Line Items]
Number of Securities, Less than 12 Months | securities	48	17
Estimated Fair Value, Less than 12 Months	$ 248.4	$ 145.3
Gross Unrealized Losses, Less than 12 Months	$ (1.6)	$ (0.3)
Number of Securities, 12 Months or Greater | securities	2	2
Estimated Fair Value, 12 Months or Greater	$ 0.9	$ 0.9
Gross Unrealized Losses, 12 Months or Greater	$ 0.0	$ 0.0
Fixed Maturity Securities [Member] | Government Sponsored Securities [Member]
Investment [Line Items]
Number of Securities, Less than 12 Months | securities	13	2
Estimated Fair Value, Less than 12 Months	$ 18.3	$ 0.3
Gross Unrealized Losses, Less than 12 Months	$ (0.1)	$ 0.0
Number of Securities, 12 Months or Greater | securities	6	16
Estimated Fair Value, 12 Months or Greater	$ 8.2	$ 29.3
Gross Unrealized Losses, 12 Months or Greater	$ (0.1)	$ (0.4)
Fixed Maturity Securities [Member] | States, Municipalities And Political Subdivisions, Tax-Exempt [Member]
Investment [Line Items]
Number of Securities, Less than 12 Months | securities	198	136
Estimated Fair Value, Less than 12 Months	$ 467.8	$ 315.6
Gross Unrealized Losses, Less than 12 Months	$ (4.0)	$ (1.8)
Number of Securities, 12 Months or Greater | securities	43	80
Estimated Fair Value, 12 Months or Greater	$ 83.0	$ 174.3
Gross Unrealized Losses, 12 Months or Greater	$ (5.2)	$ (3.0)
Fixed Maturity Securities [Member] | Corporate Securities [Member]
Investment [Line Items]
Number of Securities, Less than 12 Months | securities	2,492	1,802
Estimated Fair Value, Less than 12 Months	$ 4,912.3	$ 3,213.3
Gross Unrealized Losses, Less than 12 Months	$ (267.2)	$ (123.1)
Number of Securities, 12 Months or Greater | securities	372	314
Estimated Fair Value, 12 Months or Greater	$ 447.0	$ 514.6
Gross Unrealized Losses, 12 Months or Greater	$ (110.5)	$ (43.2)
Fixed Maturity Securities [Member] | Residential Mortgage-Backed Securities [Member]
Investment [Line Items]
Number of Securities, Less than 12 Months | securities	298	78
Estimated Fair Value, Less than 12 Months	$ 668.3	$ 155.0
Gross Unrealized Losses, Less than 12 Months	$ (7.6)	$ (1.0)
Number of Securities, 12 Months or Greater | securities	119	186
Estimated Fair Value, 12 Months or Greater	$ 186.3	$ 398.3
Gross Unrealized Losses, 12 Months or Greater	$ (7.2)	$ (8.6)
Fixed Maturity Securities [Member] | Commercial Mortgage-Backed Securities [Member]
Investment [Line Items]
Number of Securities, Less than 12 Months | securities	66	43
Estimated Fair Value, Less than 12 Months	$ 263.0	$ 156.2
Gross Unrealized Losses, Less than 12 Months	$ (4.3)	$ (0.6)
Number of Securities, 12 Months or Greater | securities	17	10
Estimated Fair Value, 12 Months or Greater	$ 38.5	$ 33.2
Gross Unrealized Losses, 12 Months or Greater	$ (0.4)	$ (0.4)
Fixed Maturity Securities [Member] | Other Debt Securities [Member]
Investment [Line Items]
Number of Securities, Less than 12 Months | securities	153	79
Estimated Fair Value, Less than 12 Months	$ 488.2	$ 270.6
Gross Unrealized Losses, Less than 12 Months	$ (5.8)	$ (1.7)
Number of Securities, 12 Months or Greater | securities	28	21
Estimated Fair Value, 12 Months or Greater	$ 77.0	$ 65.0
Gross Unrealized Losses, 12 Months or Greater	$ (2.6)	$ (1.6)
Equity Securities [Member]
Investment [Line Items]
Number of Securities, Less than 12 Months | securities	792	407
Estimated Fair Value, Less than 12 Months	$ 261.1	$ 125.4
Gross Unrealized Losses, Less than 12 Months	$ (30.9)	$ (11.1)
Number of Securities, 12 Months or Greater | securities	0	0
Estimated Fair Value, 12 Months or Greater	$ 0.0	$ 0.0
Gross Unrealized Losses, 12 Months or Greater	$ 0.0	$ 0.0