Fair Values of Financial Instruments Level 3 Quantitative Sensitivity Analysis (Details) (Fair Value, Inputs, Level 3 [Member], USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Public_Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fair Value, Investments, Valuation Techniques	- Comparability Adjustment
Investments, Fair Value Disclosure, Significant Assumptions	0.20% - 0.20%/0.20%	[1]
Mortgage/Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fair Value, Investments, Valuation Techniques	- Discount for Size
Investments, Fair Value Disclosure, Significant Assumptions	5.77% - 5.86%/5.84%	[1]
All Other Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fair Value, Investments, Valuation Techniques	- Change in Benchmark Reference - Comparability Adjustment - Discount for Size - Lack of Marketability - Volatility of Credit - Market Convention
Investments, Fair Value Disclosure, Significant Assumptions	(0.05)% - 2.60%/0.15% (0.50)% - (0.50)%/(0.50)% 0.50% - 0.50%/0.50% 0.01% - 1.00%/0.22% (0.50)% - 6.92%/1.37% Priced at Par	[1],[2],[3],[4],[5]
Corporate Bond Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fair Value, Investments, Valuation Techniques	- Comparability Adjustment - Discount for Size - Lack of Marketability - Volatility of Credit - Market Convention
Investments, Fair Value Disclosure, Significant Assumptions	(1.24)% - 0.50%/(0.16)% 0.00% - 0.10%/0.04% 0.01% - 0.40%/0.19% 0.01% - 0.01%/0.01% Priced at Par	[6]
Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fair Value, Investments, Valuation Techniques	- Market Convention
Investments, Fair Value Disclosure, Significant Assumptions	Priced at Cost or Owner's Equity	[3]
Embedded Derivative in Modified Coinsurance Arrangement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fair Value, Derivative Financial Instruments, Liabilities, Valuation Techniques	- Projected Liability Cash Flows
Investments, Fair Value Disclosure, Significant Assumptions	Actuarial Assumptions	[7]
Estimate of Fair Value, Fair Value Disclosure [Member] | Public_Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fixed Maturity Securities	17.4	[6]
Estimate of Fair Value, Fair Value Disclosure [Member] | Mortgage/Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fixed Maturity Securities	0.5	[1]
Estimate of Fair Value, Fair Value Disclosure [Member] | All Other Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fixed Maturity Securities	485.1	[1],[2],[3],[4],[5],[6]
Estimate of Fair Value, Fair Value Disclosure [Member] | Corporate Bond Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fixed Maturity Securities	115.9	[1],[3],[4],[5],[6]
Estimate of Fair Value, Fair Value Disclosure [Member] | Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Equity Securities	4.1	[3]
Estimate of Fair Value, Fair Value Disclosure [Member] | Embedded Derivative in Modified Coinsurance Arrangement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative Liability	(107.0)	[7]

[1] Represents basis point adjustments based on issue/issuer size relative to the benchmark

[2] Represents basis point adjustments for changes in benchmark spreads associated with various ratings categories

[3] Represents a decision to price based on par value, cost, or owner's equity when limited data is available

[4] Represents basis point adjustments for credit-specific factors

[5] Represents basis point adjustments to apply a discount due to the illiquidity of an investment

[6] Represents basis point adjustments for changes in benchmark spreads associated with various industry sectors

[7] Represents various actuarial assumptions required to derive the liability cash flows including incidence, termination, and lapse rates