Investments - Estimated Fair Value of Investments in Fixed Maturities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Other Receivables	$ 206.1	$ 218.7
Asset-backed Securities Not Due at a Single Maturity Date, Fair Value	213.4
Investments in Fixed Maturities, Fair Value	4,860.2	4,773.4
Accrued Expenses and Other Liabilities	431.4	403.3
US Government and Government Agencies and Authorities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in Fixed Maturities, Fair Value	428.9	491.7
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Schedule of Available-for-sale Securities [Line Items]
Asset-backed Securities Not Due at a Single Maturity Date, Fair Value	189.3
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Schedule of Available-for-sale Securities [Line Items]
Asset-backed Securities Not Due at a Single Maturity Date, Fair Value	19.6
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Schedule of Available-for-sale Securities [Line Items]
Asset-backed Securities Not Due at a Single Maturity Date, Fair Value	0.6
Other Issuers [Member]
Schedule of Available-for-sale Securities [Line Items]
Asset-backed Securities Not Due at a Single Maturity Date, Fair Value	3.9
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in Fixed Maturities, Fair Value	1,401.4	1,852.6
Corporate Bonds and Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in Fixed Maturities, Fair Value	2,993.4	2,342.3
Redeemable Preferred Stocks [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in Fixed Maturities, Fair Value	32.6	81.7
Mortgage and Asset Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in Fixed Maturities, Fair Value	3.9	5.1
Investments in Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Other Receivables	0	0
Investments in Fixed Maturities, Fair Value	4,860.2	4,773.4
Accrued Expenses and Other Liabilities	$ 1.5	$ 0

Amount of debt securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 137

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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Reference 7: http://www.xbrl.org/2003/role/presentationRef

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Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

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