Debt (Schedule of Long-Term Debt) (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Total principal debt	$ 861.2	$ 607.3
Unamortized fair value adjustment	(0.4)	(0.5)
Unamortized debt issuance costs	(2.9)	(0.9)
Long-term debt	857.9	605.9
Junior Debentures [Member]
Long-term debt	74.2	129.2
Senior Debentures (Unsecured) Maturing March 1, 2020 [Member]
Long-term debt	200.0	200.0
Senior Debentures (Unsecured) Maturing June 15, 2021 [Member]
Long-term debt	300.0
Senior debentures (unsecured) maturing October 15, 2025 [Member]
Long-term debt	121.6	121.6
FHLBB Borrowings [Member]
Long-term debt	143.4	134.5
Capital Securities [Member]
Long-term debt	18.0	18.0
Surplus Notes [Member]
Long-term debt	$ 4.0	$ 4.0

Including current and noncurrent portions, aggregate carrying amount of long-term borrowings as of the balance sheet date before deducting unamortized discount or premiums (if any). May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer.

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Including current and noncurrent portions, aggregate carrying amount of long-term borrowings as of the balance sheet date. May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any.

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