Investments (Fixed Maturities And Equity Securities In An Unrealized Loss Position) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	$ 25.9	$ 45.8
12 months or less, Fair Value	835.4	1,389.6
Greater than 12 months, Gross Unrealized Losses	11.7	18.0
Greater than 12 months, Fair Value	116.5	123.6
Total, Gross Unrealized Losses	37.6	63.8
Total, Fair Value	951.9	1,513.2
Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	19.4	37.0
12 months or less, Fair Value	746.8	1,302.4
Greater than 12 months, Gross Unrealized Losses	11.3	18.0
Greater than 12 months, Fair Value	105.9	123.6
Total, Gross Unrealized Losses	30.7	55.0
Total, Fair Value	852.7	1,426.0
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	6.5	8.8
12 months or less, Fair Value	88.6	87.2
Greater than 12 months, Gross Unrealized Losses	0.4
Greater than 12 months, Fair Value	10.6
Total, Gross Unrealized Losses	6.9	8.8
Total, Fair Value	99.2	87.2
Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	10.6	27.1
12 months or less, Fair Value	636.1	1,175.5
Greater than 12 months, Gross Unrealized Losses	9.3	14.3
Greater than 12 months, Fair Value	93.5	108.9
Total, Gross Unrealized Losses	19.9	41.4
Total, Fair Value	729.6	1,284.4
Investment Grade [Member] | U.S. Treasury And Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	0.3	0.2
12 months or less, Fair Value	42.2	57.7
Total, Gross Unrealized Losses	0.3	0.2
Total, Fair Value	42.2	57.7
Investment Grade [Member] | Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	0.1	0.5
12 months or less, Fair Value	74.2	148.8
Total, Gross Unrealized Losses	0.1	0.5
Total, Fair Value	74.2	148.8
Investment Grade [Member] | Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	4.6	19.9
12 months or less, Fair Value	364.8	699.6
Greater than 12 months, Gross Unrealized Losses	4.7	8.2
Greater than 12 months, Fair Value	32.6	35.6
Total, Gross Unrealized Losses	9.3	28.1
Total, Fair Value	397.4	735.2
Investment Grade [Member] | Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	0.5	0.5
12 months or less, Fair Value	21.9	28.0
Greater than 12 months, Gross Unrealized Losses	2.4	3.4
Greater than 12 months, Fair Value	42.2	58.8
Total, Gross Unrealized Losses	2.9	3.9
Total, Fair Value	64.1	86.8
Investment Grade [Member] | Residential Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	4.6	5.1
12 months or less, Fair Value	52.4	115.8
Greater than 12 months, Gross Unrealized Losses	2.0	2.4
Greater than 12 months, Fair Value	13.9	9.9
Total, Gross Unrealized Losses	6.6	7.5
Total, Fair Value	66.3	125.7
Investment Grade [Member] | Commercial Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	0.1	0.7
12 months or less, Fair Value	24.3	58.0
Greater than 12 months, Gross Unrealized Losses	0.2	0.3
Greater than 12 months, Fair Value	4.8	4.6
Total, Gross Unrealized Losses	0.3	1.0
Total, Fair Value	29.1	62.6
Investment Grade [Member] | Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	0.4	0.2
12 months or less, Fair Value	56.3	67.6
Total, Gross Unrealized Losses	0.4	0.2
Total, Fair Value	56.3	67.6
Below Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	8.8	9.9
12 months or less, Fair Value	110.7	126.9
Greater than 12 months, Gross Unrealized Losses	2.0	3.7
Greater than 12 months, Fair Value	12.4	14.7
Total, Gross Unrealized Losses	10.8	13.6
Total, Fair Value	123.1	141.6
Below Investment Grade [Member] | Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	7.4	8.5
12 months or less, Fair Value	93.3	118.0
Greater than 12 months, Gross Unrealized Losses	2.0	3.7
Greater than 12 months, Fair Value	12.4	14.7
Total, Gross Unrealized Losses	9.4	12.2
Total, Fair Value	105.7	132.7
Below Investment Grade [Member] | Residential Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	0.8	0.9
12 months or less, Fair Value	16.4	8.0
Total, Gross Unrealized Losses	0.8	0.9
Total, Fair Value	16.4	8.0
Below Investment Grade [Member] | Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	0.6	0.5
12 months or less, Fair Value	1.0	0.9
Total, Gross Unrealized Losses	0.6	0.5
Total, Fair Value	$ 1.0	$ 0.9