Investments - Aging of Unrealized Losses on Investments in Fixed Maturities and Equity Securities (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Less than Twelve Months, Fair Value	$ 343.9	$ 259.5
Less than 12 Months, Unrealized Losses	(7.6)	(16.7)
Twelve Months or Longer, Fair Value	54.6	94.6
12 Months or Longer, Unrealized Losses	(3.8)	(6.6)
Fair Value	398.5	354.1
Unrealized Losses	(11.4)	(23.3)
Available For Sale Securities, Continuous Unrealized Loss Position, Credit Losses Recognized Related to Securites in An Unrealized Loss Position	(0.3)
Available For Sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses Related to Securities that have Previously Recognized Foregin Currency Impairment	0.1	0.2
Number of Issuers of Available for Sales Securities Continuous Unrealized Loss Possition Aggregate Losses Related to Securities that have Previously Recognized Foreign Currency impairment	1	1
US Government and Government Agencies and Authorities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than Twelve Months, Fair Value	40.8	1.3
Less than 12 Months, Unrealized Losses	(0.2)	0
Twelve Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Fair Value	40.8	1.3
Unrealized Losses	(0.2)	0
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than Twelve Months, Fair Value	6.3	2.0
Less than 12 Months, Unrealized Losses	(0.1)	0
Twelve Months or Longer, Fair Value	0.3	12.0
12 Months or Longer, Unrealized Losses	0	(0.8)
Fair Value	6.6	14.0
Unrealized Losses	(0.1)	(0.8)
Corporate Bonds and Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than Twelve Months, Fair Value	268.5	169.6
Less than 12 Months, Unrealized Losses	(5.2)	(5.1)
Twelve Months or Longer, Fair Value	38.1	74.7
12 Months or Longer, Unrealized Losses	(2.3)	(4.3)
Fair Value	306.6	244.3
Unrealized Losses	(7.5)	(9.4)
Redeemable Preferred Stocks [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than Twelve Months, Fair Value	0	0.6
Less than 12 Months, Unrealized Losses	0	(0.1)
Twelve Months or Longer, Fair Value	0.4	0.1
12 Months or Longer, Unrealized Losses	0	0
Fair Value	0.4	0.7
Unrealized Losses	0	(0.1)
Mortgage and Asset Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than Twelve Months, Fair Value	0	0
Less than 12 Months, Unrealized Losses	0	0
Twelve Months or Longer, Fair Value	1.7	2.7
12 Months or Longer, Unrealized Losses	(0.3)	(0.8)
Fair Value	1.7	2.7
Unrealized Losses	(0.3)	(0.8)
Investments in Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than Twelve Months, Fair Value	315.6	173.5
Less than 12 Months, Unrealized Losses	(5.5)	(5.2)
Twelve Months or Longer, Fair Value	40.5	89.5
12 Months or Longer, Unrealized Losses	(2.6)	(5.9)
Fair Value	356.1	263.0
Unrealized Losses	(8.1)	(11.1)
Preferred Stocks Finance, Insurance and Real Estate [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than Twelve Months, Fair Value	0	54.9
Less than 12 Months, Unrealized Losses	0	(8.1)
Twelve Months or Longer, Fair Value	2.4	2.2
12 Months or Longer, Unrealized Losses	(0.1)	(0.6)
Fair Value	2.4	57.1
Unrealized Losses	(0.1)	(8.7)
Preferred Stocks Other Industries [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than Twelve Months, Fair Value	2.3	1.8
Less than 12 Months, Unrealized Losses	(0.8)	0
Twelve Months or Longer, Fair Value	3.7	2.8
12 Months or Longer, Unrealized Losses	(0.1)	(0.1)
Fair Value	6.0	4.6
Unrealized Losses	(0.9)	(0.1)
Common Stocks Manufacturing [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than Twelve Months, Fair Value	6.3	1.5
Less than 12 Months, Unrealized Losses	(0.4)	(0.1)
Twelve Months or Longer, Fair Value	0	0.1
12 Months or Longer, Unrealized Losses	0	0
Fair Value	6.3	1.6
Unrealized Losses	(0.4)	(0.1)
Common Stock Other Industries [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than Twelve Months, Fair Value	14.2	10.7
Less than 12 Months, Unrealized Losses	(0.4)	(1.8)
Twelve Months or Longer, Fair Value	1.3	0
12 Months or Longer, Unrealized Losses	(0.1)	0
Fair Value	15.5	10.7
Unrealized Losses	(0.5)	(1.8)
Limited Liability Companies and Limited Partnerships [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than Twelve Months, Fair Value	5.5	17.1
Less than 12 Months, Unrealized Losses	(0.5)	(1.5)
Twelve Months or Longer, Fair Value	6.7	0
12 Months or Longer, Unrealized Losses	(0.9)	0
Fair Value	12.2	17.1
Unrealized Losses	(1.4)	(1.5)
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than Twelve Months, Fair Value	28.3	86.0
Less than 12 Months, Unrealized Losses	(2.1)	(11.5)
Twelve Months or Longer, Fair Value	14.1	5.1
12 Months or Longer, Unrealized Losses	(1.2)	(0.7)
Fair Value	42.4	91.1
Unrealized Losses	(3.3)	(12.2)
External Credit Rating, Investment Grade [Member] | Investments in Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized Losses	3.8	(5.7)
External Credit Rating, Non Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Related to Securities that have Previously Recognized Foregin Currency Impairment	(0.1)	(0.2)
Percentage of Unrealized Loss Postion to Amortized Cost Basis of Available for Sale Security Average	3.00%	4.00%
External Credit Rating, Non Investment Grade [Member] | Investments in Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized Losses	$ 4.3	$ (5.4)