Investments (Fixed Maturities and Equity Securities Unrealized Loss Position) (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Below Investment Grade [Member]
12 months or less, Gross Unrealized Losses	$ 12.3	$ 25.8
12 months or less, Fair Value	553.5	829.2
Greater than 12 months, Gross Unrealized Losses	32.0	41.7
Greater than 12 months, Fair Value	273.2	298.2
Total, Gross Unrealized Losses	44.3	67.5
Total, Fair Value	826.7	1,127.4
Below Investment Grade [Member] | Corporate [Member]
12 months or less, Gross Unrealized Losses	1.1	1.0
12 months or less, Fair Value	53.6	51.1
Greater than 12 months, Gross Unrealized Losses	9.8	12.0
Greater than 12 months, Fair Value	89.2	90.0
Total, Gross Unrealized Losses	10.9	13.0
Total, Fair Value	142.8	141.1
Below Investment Grade [Member] | Fixed Maturities [Member]
12 months or less, Gross Unrealized Losses	11.7	23.9
12 months or less, Fair Value	538.6	783.4
Greater than 12 months, Gross Unrealized Losses	32.0	41.7
Greater than 12 months, Fair Value	273.2	298.2
Total, Gross Unrealized Losses	43.7	65.6
Total, Fair Value	811.8	1,081.6
Below Investment Grade [Member] | Equity Securities [Member]
12 months or less, Gross Unrealized Losses	0.6	1.9
12 months or less, Fair Value	14.9	45.8
Total, Gross Unrealized Losses	0.6	1.9
Total, Fair Value	14.9	45.8
Investment Grade [Member]
12 months or less, Gross Unrealized Losses	10.6	22.9
12 months or less, Fair Value	485.0	732.3
Greater than 12 months, Gross Unrealized Losses	22.2	29.7
Greater than 12 months, Fair Value	184.0	208.2
Total, Gross Unrealized Losses	32.8	52.6
Total, Fair Value	669.0	940.5
Investment Grade [Member] | U.S. Treasury and Government Agencies [Member]
12 months or less, Gross Unrealized Losses	1.8	2.7
12 months or less, Fair Value	70.0	84.9
Greater than 12 months, Gross Unrealized Losses	0.3	0.5
Greater than 12 months, Fair Value	15.7	16.4
Total, Gross Unrealized Losses	2.1	3.2
Total, Fair Value	85.7	101.3
Investment Grade [Member] | Corporate [Member]
12 months or less, Gross Unrealized Losses	3.5	6.7
12 months or less, Fair Value	167.5	256.1
Greater than 12 months, Gross Unrealized Losses	8.3	10.5
Greater than 12 months, Fair Value	58.6	66.8
Total, Gross Unrealized Losses	11.8	17.2
Total, Fair Value	226.1	322.9
Investment Grade [Member] | Municipal [Member]
12 months or less, Gross Unrealized Losses	3.0	10.3
12 months or less, Fair Value	147.9	289.1
Greater than 12 months, Gross Unrealized Losses	6.2	9.0
Greater than 12 months, Fair Value	79.9	86.7
Total, Gross Unrealized Losses	9.2	19.3
Total, Fair Value	227.8	375.8
Investment Grade [Member] | Residential Mortgage-Backed [Member]
12 months or less, Gross Unrealized Losses	2.1	3.1
12 months or less, Fair Value	81.0	89.1
Greater than 12 months, Gross Unrealized Losses	7.1	8.8
Greater than 12 months, Fair Value	25.1	31.0
Total, Gross Unrealized Losses	9.2	11.9
Total, Fair Value	106.1	120.1
Investment Grade [Member] | Commercial Mortgage-Backed [Member]
12 months or less, Gross Unrealized Losses	0.2	0.1
12 months or less, Fair Value	18.6	13.1
Greater than 12 months, Gross Unrealized Losses	0.3	0.9
Greater than 12 months, Fair Value	4.7	7.3
Total, Gross Unrealized Losses	0.5	1.0
Total, Fair Value	$ 23.3	$ 20.4