Fair Value Measurements - Fair Value Inputs (Details) (USD $) In Millions, unless otherwise specified																																																																																																																				12 Months Ended					12 Months Ended
	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Investments in Fixed Maturities [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Investments in Fixed Maturities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] US Government and Government Agencies and Authorities [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] US Government and Government Agencies and Authorities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] States and Political Subdivisions [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] States and Political Subdivisions [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Corporate Bonds and Notes [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Corporate Bonds and Notes [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Redeemable Preferred Stocks [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Redeemable Preferred Stocks [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Mortgage and Asset Backed [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Mortgage and Asset Backed [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Equity Securities [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Equity Securities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Preferred Stocks Finance, Insurance and Real Estate [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Preferred Stocks Finance, Insurance and Real Estate [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Preferred Stocks Other Industries [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Preferred Stocks Other Industries [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Common Stock Manufacturing [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Common Stock Manufacturing [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Common Stock Other Industries [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Common Stock Other Industries [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Exchange Traded Funds [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Exchange Traded Funds [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Limited Liability Companies and Limited Partnerships [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Limited Liability Companies and Limited Partnerships [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Investments in Fixed Maturities [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Investments in Fixed Maturities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] US Government and Government Agencies and Authorities [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] US Government and Government Agencies and Authorities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] States and Political Subdivisions [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] States and Political Subdivisions [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Corporate Bonds and Notes [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Corporate Bonds and Notes [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Redeemable Preferred Stocks [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Redeemable Preferred Stocks [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Mortgage and Asset Backed [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Mortgage and Asset Backed [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Equity Securities [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Equity Securities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Preferred Stocks Finance, Insurance and Real Estate [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Preferred Stocks Finance, Insurance and Real Estate [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Preferred Stocks Other Industries [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Preferred Stocks Other Industries [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Common Stock Manufacturing [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Common Stock Manufacturing [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Common Stock Other Industries [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Common Stock Other Industries [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Exchange Traded Funds [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Exchange Traded Funds [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Limited Liability Companies and Limited Partnerships [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Limited Liability Companies and Limited Partnerships [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Investments in Fixed Maturities [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Investments in Fixed Maturities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] US Government and Government Agencies and Authorities [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] US Government and Government Agencies and Authorities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] States and Political Subdivisions [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] States and Political Subdivisions [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Corporate Bonds and Notes [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Corporate Bonds and Notes [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Redeemable Preferred Stocks [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Redeemable Preferred Stocks [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Mortgage and Asset Backed [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Mortgage and Asset Backed [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Equity Securities [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Equity Securities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Preferred Stocks Finance, Insurance and Real Estate [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Preferred Stocks Finance, Insurance and Real Estate [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Preferred Stocks Other Industries [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Preferred Stocks Other Industries [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Common Stock Manufacturing [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Common Stock Manufacturing [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Common Stock Other Industries [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Common Stock Other Industries [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Exchange Traded Funds [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Exchange Traded Funds [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Limited Liability Companies and Limited Partnerships [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Limited Liability Companies and Limited Partnerships [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Investments in Fixed Maturities [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Investments in Fixed Maturities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member] US Government and Government Agencies and Authorities [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member] US Government and Government Agencies and Authorities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member] States and Political Subdivisions [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member] States and Political Subdivisions [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Corporate Bonds and Notes [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Corporate Bonds and Notes [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Redeemable Preferred Stocks [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Redeemable Preferred Stocks [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Mortgage and Asset Backed [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Mortgage and Asset Backed [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Equity Securities [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Equity Securities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Preferred Stocks Finance, Insurance and Real Estate [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Preferred Stocks Finance, Insurance and Real Estate [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Preferred Stocks Other Industries [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Preferred Stocks Other Industries [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Common Stock Manufacturing [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Common Stock Manufacturing [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Common Stock Other Industries [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Common Stock Other Industries [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Exchange Traded Funds [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Exchange Traded Funds [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Limited Liability Companies and Limited Partnerships [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member] Fair Value [Member] Limited Liability Companies and Limited Partnerships [Member]	Dec. 31, 2012 Other Debt Obligations [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Investments in Fixed Maturities [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 External Credit Rating, Investment Grade [Member] Private Placement [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 External Credit Rating, Investment Grade [Member] Minimum [Member] Private Placement [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 External Credit Rating, Investment Grade [Member] Maximum [Member] Private Placement [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 External Credit Rating, Investment Grade [Member] Weighted Average [Member] Private Placement [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 External Credit Rating, Non Investment Grade [Member] Senior Debt Obligations [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 External Credit Rating, Non Investment Grade [Member] Junior Subordinated Debt [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 External Credit Rating, Non Investment Grade [Member] Minimum [Member] Senior Debt Obligations [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 External Credit Rating, Non Investment Grade [Member] Minimum [Member] Junior Subordinated Debt [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 External Credit Rating, Non Investment Grade [Member] Maximum [Member] Senior Debt Obligations [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 External Credit Rating, Non Investment Grade [Member] Maximum [Member] Junior Subordinated Debt [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 External Credit Rating, Non Investment Grade [Member] Weighted Average [Member] Senior Debt Obligations [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 External Credit Rating, Non Investment Grade [Member] Weighted Average [Member] Junior Subordinated Debt [Member] Market Approach Valuation Technique [Member] Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure			$ 135.8	$ 153.6	$ 135.8	$ 153.6	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 265.6	$ 184.1	$ 0	$ 0	$ 0	$ 0	$ 79.6	$ 74.7	$ 60.1	$ 42.8	$ 125.9	$ 66.6	$ 0	$ 0			$ 4,358.6	$ 4,378.3	$ 293.1	$ 338.1	$ 1,401.4	$ 1,852.6	$ 2,632.4	$ 2,107.2	$ 27.9	$ 75.6	$ 3.8	$ 4.8	$ 101.7	$ 106.6	$ 79.2	$ 86.7	$ 15.3	$ 14.9	$ 6.0	$ 5.0	$ 1.2	$ 0	$ 0	$ 0	$ 0	$ 0			$ 365.8	$ 241.5	$ 0	$ 0	$ 0	$ 0	$ 361.0	$ 235.1	$ 4.7	$ 6.1	$ 0.1	$ 0.3	$ 154.6	$ 106.6	$ 0	$ 0	$ 6.0	$ 5.6	$ 1.9	$ 3.7	$ 5.4	$ 4.2	$ 0	$ 0	$ 141.3	$ 93.1			$ 4,860.2	$ 4,773.4	$ 428.9	$ 491.7	$ 1,401.4	$ 1,852.6	$ 2,993.4	$ 2,342.3	$ 32.6	$ 81.7	$ 3.9	$ 5.1	$ 521.9	$ 397.3	$ 79.2	$ 86.7	$ 21.3	$ 20.5	$ 87.5	$ 83.4	$ 66.7	$ 47.0	$ 125.9	$ 66.6	$ 141.3	$ 93.1
Trading Securities, Fair Value Disclosure	4.5	4.4																											0	0																											0	0																											4.5	4.4
Investments, Fair Value Disclosure	405.9	342.1																											4,460.3	4,484.9																											520.4	348.1																											5,386.6	5,175.1
Assets, Fair Value Disclosure																																																																																																																	$ 15.5	$ 361.0	$ 94.6				$ 77.7	$ 173.2
Fair Value Inputs, Discount Rate																																																																																																																				1.30%	6.30%	4.00%			5.70%	8.80%	18.00%	21.40%	9.10%	14.80%