Investments - Schedule of Investments (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	$ 4,416.3
Amortized Cost Basis	477.2	462.7
Fixed Maturities at Fair Value	4,701.1	4,860.2
Fair Value	545.0	521.9
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Due in One Year or Less - Amortized Cost	115.0
Due in One Year or Less - Fair Value	117.8
Due after One Year to Five Years - Amortized Cost	641.9
Due after One Year to Five Years - Fair Value	675.9
Due after Five Years to Ten Years - Amortized Cost	1,259.5
Due after Five Years to Ten Years - Fair Value	1,295.9
Due after Ten Years - Amortized Cost	2,182.3
Due after Ten Years - Fair Value	2,383.4
Asset-backed Securities Not Due in a Single Maturity Date - Amortized Cost	217.6
Asset-backed Securities Not Due in a Single Maturity Date - Fair Value	228.1
Other Receivables	206.2	206.1
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	1,248.4	343.9
Less Than 12 Months, Unrealized Losses	(68.0)	(7.6)
12 Months or Longer, Fair Value	71.4	54.6
12 Months or Longer, Unrealized Losses	(4.7)	(3.8)
Total, Fair Value	1,319.8	398.5
Total, Unrealized Losses	(72.7)	(11.4)
Available For Sale Securities, Continuous Unrealized Loss Position, Credit Losses Recognized Related to Securites in An Unrealized Loss Position, In a Position of 12 Months or Longer	(0.5)	0
Less Than 12 Months, Fair Value	(1.3)	(0.3)
Available For Sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses Related to Securities that have Previously Recognized Foreign Currency Impairment	0.1
Other Liabilities	448.5	431.4
Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	4,416.3	4,283.8
Gross Unrealized Gains	351.4	584.5
Gross Unrealized Losses	(66.6)	(8.1)
Fixed Maturities at Fair Value	4,701.1	4,860.2
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Other Receivables	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	1,084.0	315.6
Less Than 12 Months, Unrealized Losses	(62.7)	(5.5)
12 Months or Longer, Fair Value	61.6	40.5
12 Months or Longer, Unrealized Losses	(3.9)	(2.6)
Total, Fair Value	1,145.6	356.1
Total, Unrealized Losses	(66.6)	(8.1)
Other Liabilities	6.2	1.5
Collateralized Loan Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed Maturities at Fair Value	29.8
US Government and Government Agencies and Authorities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	372.5	384.0
Gross Unrealized Gains	29.8	45.1
Gross Unrealized Losses	(7.1)	(0.2)
Fixed Maturities at Fair Value	395.2	428.9
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	89.5	40.8
Less Than 12 Months, Unrealized Losses	(7.1)	(0.2)
12 Months or Longer, Fair Value	0.1	0
12 Months or Longer, Unrealized Losses	0	0
Total, Fair Value	89.6	40.8
Total, Unrealized Losses	(7.1)	(0.2)
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Asset-backed Securities Not Due in a Single Maturity Date - Fair Value	175.3
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Asset-backed Securities Not Due in a Single Maturity Date - Fair Value	14.3
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Asset-backed Securities Not Due in a Single Maturity Date - Fair Value	0.5
Other Issuers [Member]
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Asset-backed Securities Not Due in a Single Maturity Date - Fair Value	38.0
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,333.7	1,251.0
Gross Unrealized Gains	83.6	150.5
Gross Unrealized Losses	(16.1)	(0.1)
Fixed Maturities at Fair Value	1,401.2	1,401.4
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	216.8	6.3
Less Than 12 Months, Unrealized Losses	(16.1)	(0.1)
12 Months or Longer, Fair Value	0.3	0.3
12 Months or Longer, Unrealized Losses	0	0
Total, Fair Value	217.1	6.6
Total, Unrealized Losses	(16.1)	(0.1)
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	0.6
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fixed Maturities at Fair Value	0.6
Bonds and Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2,669.9	2,615.5
Gross Unrealized Gains	234.3	385.4
Gross Unrealized Losses	(42.4)	(7.5)
Fixed Maturities at Fair Value	2,861.8	2,993.4
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	754.4	268.5
Less Than 12 Months, Unrealized Losses	(38.6)	(5.2)
12 Months or Longer, Fair Value	59.6	38.1
12 Months or Longer, Unrealized Losses	(3.8)	(2.3)
Total, Fair Value	814.0	306.6
Total, Unrealized Losses	(42.4)	(7.5)
Redeemable Preferred Stocks [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2.1	30.1
Gross Unrealized Gains	2.2	2.5
Gross Unrealized Losses	0	0
Fixed Maturities at Fair Value	4.3	32.6
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value		0
Less Than 12 Months, Unrealized Losses		0
12 Months or Longer, Fair Value		0.4
12 Months or Longer, Unrealized Losses		0
Total, Fair Value		0.4
Total, Unrealized Losses		0
Mortgage and Asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	37.5	3.2
Gross Unrealized Gains	1.5	1.0
Gross Unrealized Losses	(1.0)	(0.3)
Fixed Maturities at Fair Value	38.0	3.9
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	23.3	0
Less Than 12 Months, Unrealized Losses	(0.9)	0
12 Months or Longer, Fair Value	1.6	1.7
12 Months or Longer, Unrealized Losses	(0.1)	(0.3)
Total, Fair Value	24.9	1.7
Total, Unrealized Losses	(1.0)	(0.3)
Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed Maturities at Fair Value	6.7	2.3
Non-governmental Residential Mortgage-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed Maturities at Fair Value	1.2	1.3
Other Asset Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed Maturities at Fair Value	0.3	0.3
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	477.2	462.7
Gross Unrealized Gains	73.9	62.5
Gross Unrealized Losses	(6.1)	(3.3)
Fair Value	545.0	521.9
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	164.4	28.3
Less Than 12 Months, Unrealized Losses	(5.3)	(2.1)
12 Months or Longer, Fair Value	9.8	14.1
12 Months or Longer, Unrealized Losses	(0.8)	(1.2)
Total, Fair Value	174.2	42.4
Total, Unrealized Losses	(6.1)	(3.3)
Preferred Stock Finance, Insurance and Real Estate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	75.4	75.4
Gross Unrealized Gains	3.3	3.9
Gross Unrealized Losses	(0.9)	(0.1)
Fair Value	77.8	79.2
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	14.2	0
Less Than 12 Months, Unrealized Losses	(0.8)	0
12 Months or Longer, Fair Value	2.4	2.4
12 Months or Longer, Unrealized Losses	(0.1)	(0.1)
Total, Fair Value	16.6	2.4
Total, Unrealized Losses	(0.9)	(0.1)
Preferred Stocks Other Industries [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	14.5	18.4
Gross Unrealized Gains	5.3	3.8
Gross Unrealized Losses	(0.5)	(0.9)
Fair Value	19.3	21.3
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	1.4	2.3
Less Than 12 Months, Unrealized Losses	(0.5)	(0.8)
12 Months or Longer, Fair Value	0.7	3.7
12 Months or Longer, Unrealized Losses	0	(0.1)
Total, Fair Value	2.1	6.0
Total, Unrealized Losses	(0.5)	(0.9)
Common Stocks Manufacturing [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	67.3	67.0
Gross Unrealized Gains	27.9	20.9
Gross Unrealized Losses	(0.2)	(0.4)
Fair Value	95.0	87.5
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	2.5	6.3
Less Than 12 Months, Unrealized Losses	(0.2)	(0.4)
12 Months or Longer, Fair Value	0.2	0
12 Months or Longer, Unrealized Losses	0	0
Total, Fair Value	2.7	6.3
Total, Unrealized Losses	(0.2)	(0.4)
Common Stocks Other Industries [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	49.8	59.1
Gross Unrealized Gains	17.2	8.1
Gross Unrealized Losses	(0.4)	(0.5)
Fair Value	66.6	66.7
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	2.2	14.2
Less Than 12 Months, Unrealized Losses	(0.4)	(0.4)
12 Months or Longer, Fair Value	0.5	1.3
12 Months or Longer, Unrealized Losses	0	(0.1)
Total, Fair Value	2.7	15.5
Total, Unrealized Losses	(0.4)	(0.5)
Exchange Traded Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	140.2	119.6
Gross Unrealized Gains	0.3	6.3
Gross Unrealized Losses	(1.5)	0
Fair Value	139.0	125.9
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	82.2
Less Than 12 Months, Unrealized Losses	(1.5)
12 Months or Longer, Fair Value	0
12 Months or Longer, Unrealized Losses	0
Total, Fair Value	82.2
Total, Unrealized Losses	(1.5)
Limited Liability Companies and Limited Partnerships [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	130.0	123.2
Gross Unrealized Gains	19.9	19.5
Gross Unrealized Losses	(2.6)	(1.4)
Fair Value	147.3	141.3
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	61.9	5.5
Less Than 12 Months, Unrealized Losses	(1.9)	(0.5)
12 Months or Longer, Fair Value	6.0	6.7
12 Months or Longer, Unrealized Losses	(0.7)	(0.9)
Total, Fair Value	67.9	12.2
Total, Unrealized Losses	(2.6)	(1.4)
External Credit Rating, Investment Grade [Member] | Fixed Maturities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Total, Unrealized Losses	61.3	3.8
External Credit Rating, Non Investment Grade [Member] | Fixed Maturities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Total, Unrealized Losses	5.3	4.3
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Related to Securities that have Previously Recognized Foreign Currency Impairment	$ (0.1)	$ (0.1)
Number of Issuers of Available for Sales Securities Continuous Unrealized Loss Position Aggregate Losses Related to Securities that have Previously Recognized Foreign Currency impairment	(1)	1
Percentage of Unrealized Loss Postion to Amortized Cost Basis of Available for Sale Security Average	5.00%	3.00%