Quantitative Information Regarding Significant Unobservable Inputs (Details) (Fair Value, Inputs, Level 3 [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Embedded Derivative Financial Instruments [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Measurements, Significant Assumptions	Actuarial Assumptions	[1]	Actuarial Assumptions	[1]
Embedded Derivative, Fair Value of Embedded Derivative Liability	$ (77.5)		$ (83.9)
Fair Value Measurements, Valuation Techniques	- Projected Liability Cash Flows		- Projected Liability Cash Flows
US States and Political Subdivisions Debt Securities [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Measurements, Significant Assumptions	0.25% - 1.25% / 0.74%		0.25% - 0.25% / 0.25% 0.25% - 0.25% / 0.25% 0.15% - 0.15% / 0.15%
Fair value of fixed maturity securities	126.5		42.7
Fair Value Measurements, Valuation Techniques	- Comparability Adjustment		- Comparability Adjustment - Lack of Marketability - Volatility of Credit
US States and Political Subdivisions Debt Securities [Member] | Minimum [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	0.25%	[2]	0.25%	[2]
Fair Value Inputs, Entity Credit Risk			0.15%	[3]
Fair Value Inputs, Discount for Lack of Marketability			0.25%	[4]
US States and Political Subdivisions Debt Securities [Member] | Maximum [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	1.25%	[2]	0.25%	[2]
Fair Value Inputs, Entity Credit Risk			0.15%	[3]
Fair Value Inputs, Discount for Lack of Marketability			0.25%	[4]
US States and Political Subdivisions Debt Securities [Member] | Weighted Average [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	0.74%	[2]	0.25%	[2]
Fair Value Inputs, Entity Credit Risk			0.15%	[3]
Fair Value Inputs, Discount for Lack of Marketability			0.25%	[4]
Public Utilities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Measurements, Significant Assumptions	0.25% - 0.30% / 0.27% 0.25% - 0.25% / 0.25%		0.20% - 0.20% / 0.20%
Fair value of fixed maturity securities	89.2		17.4
Fair Value Measurements, Valuation Techniques	- Comparability Adjustment - Volatility of Credit		- Comparability Adjustment
Public Utilities | Minimum [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	0.25%	[2]	0.20%	[2]
Fair Value Inputs, Entity Credit Risk	0.25%	[3]
Public Utilities | Maximum [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	0.30%	[2]	0.20%	[2]
Fair Value Inputs, Entity Credit Risk	0.25%	[3]
Public Utilities | Weighted Average [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	0.27%	[2]	0.20%	[2]
Fair Value Inputs, Entity Credit Risk	0.25%	[3]
Asset-backed Securities [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Measurements, Significant Assumptions	5.76% - 5.86% / 5.84%		5.74% - 5.84% / 5.81%
Fair value of fixed maturity securities	0.5		0.5
Fair Value Measurements, Valuation Techniques	- Discount for Size		- Discount for Size
Asset-backed Securities [Member] | Minimum [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount for Size	5.76%	[5]	5.74%	[5]
Asset-backed Securities [Member] | Maximum [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount for Size	5.86%	[5]	5.84%	[5]
Asset-backed Securities [Member] | Weighted Average [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Discount for Size	5.84%	[5]	5.81%	[5]
All Other Corporate Bonds - Private
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Measurements, Significant Assumptions	0.75% - 3.20% / 1.07% (0.54)% - (0.08)% / (0.37)% 0.50% - 0.50% / 0.50% 0.50% - 1.00% / 0.76% 0.50% - 7.72% / 1.60% Priced at Par		0.04% - 2.89% / 0.28% 1.48% - 1.48% / 1.48% 0.10% - 0.50% / 0.24% 0.10% - 1.00% / 0.46% (0.25)% -7.72% / 1.51% Priced at Par
Fair value of fixed maturity securities	237.5		391.8
Fair Value Measurements, Valuation Techniques	- Change in Benchmark Reference - Comparability Adjustment - Discount for Size - Lack of Marketability - Volatility of Credit - Market Convention		- Change in Benchmark Reference - Comparability Adjustment - Discount for Size - Lack of Marketability - Volatility of Credit - Market Convention
All Other Corporate Bonds - Private | Market Convention [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Measurements, Significant Assumptions	Priced at Par	[6]	Priced at Par	[6]
All Other Corporate Bonds - Private | Minimum [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	(0.54%)	[2]	1.48%	[2]
Fair Value Inputs, Entity Credit Risk	0.50%	[3]	(0.25%)	[3]
Fair Value Inputs, Discount for Size	0.50%	[5]	0.10%	[5]
Fair Value Inputs, Change in Benchmark Reference	0.75%	[7]	0.04%	[7]
Fair Value Inputs, Discount for Lack of Marketability	0.50%	[4]	0.10%	[4]
All Other Corporate Bonds - Private | Maximum [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	(0.08%)	[2]	1.48%	[2]
Fair Value Inputs, Entity Credit Risk	7.72%	[3]	7.72%	[3]
Fair Value Inputs, Discount for Size	0.50%	[5]	0.50%	[5]
Fair Value Inputs, Change in Benchmark Reference	3.20%	[7]	2.89%	[7]
Fair Value Inputs, Discount for Lack of Marketability	1.00%	[4]	1.00%	[4]
All Other Corporate Bonds - Private | Weighted Average [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	(0.37%)	[2]	1.48%	[2]
Fair Value Inputs, Entity Credit Risk	1.60%	[3]	1.51%	[3]
Fair Value Inputs, Discount for Size	0.50%	[5]	0.24%	[5]
Fair Value Inputs, Change in Benchmark Reference	1.07%	[7]	0.28%	[7]
Fair Value Inputs, Discount for Lack of Marketability	0.76%	[4]	0.46%	[4]
Corporate Bond Securities - Public
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Measurements, Significant Assumptions	(0.88)% - (0.88)% / (0.88)% (0.30)% - 1.00% / 0.10% (0.57)% - (0.57)% / (0.57)% 0.05% - 0.20% / 0.13% (0.30)% - 0.30% / 0.10%		0.25% - 0.25% / 0.25% (0.59)% - 1.00% / 0.27% 0.25% - 0.25% / 0.25% 0.20% - 0.30% / 0.24% (0.30)% - (0.30)% / (0.30)% Priced at Par
Fair value of fixed maturity securities	328.4		165.0
Fair Value Measurements, Valuation Techniques	- Change in Benchmark Reference - Comparability Adjustment - Discount for Size - Lack of Marketability - Volatility of Credit		- Change in Benchmark Reference - Comparability Adjustment - Discount for Size - Lack of Marketability - Volatility of Credit - Market Convention
Corporate Bond Securities - Public | Market Convention [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Measurements, Significant Assumptions			Priced at Par	[6]
Corporate Bond Securities - Public | Minimum [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	(0.30%)	[2]	(0.59%)	[2]
Fair Value Inputs, Entity Credit Risk	(0.30%)	[3]	(0.30%)	[3]
Fair Value Inputs, Discount for Size	(0.57%)	[5]	0.25%	[5]
Fair Value Inputs, Change in Benchmark Reference	(0.88%)	[7]	0.25%	[7]
Fair Value Inputs, Discount for Lack of Marketability	0.05%	[4]	0.20%	[4]
Corporate Bond Securities - Public | Maximum [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	1.00%	[2]	1.00%	[2]
Fair Value Inputs, Entity Credit Risk	0.30%	[3]	(0.30%)	[3]
Fair Value Inputs, Discount for Size	(0.57%)	[5]	0.25%	[5]
Fair Value Inputs, Change in Benchmark Reference	(0.88%)	[7]	0.25%	[7]
Fair Value Inputs, Discount for Lack of Marketability	0.20%	[4]	0.30%	[4]
Corporate Bond Securities - Public | Weighted Average [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	0.10%	[2]	0.27%	[2]
Fair Value Inputs, Entity Credit Risk	0.10%	[3]	(0.30%)	[3]
Fair Value Inputs, Discount for Size	(0.57%)	[5]	0.25%	[5]
Fair Value Inputs, Change in Benchmark Reference	(0.88%)	[7]	0.25%	[7]
Fair Value Inputs, Discount for Lack of Marketability	0.13%	[4]	0.24%	[4]
Equity Securities [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Measurements, Significant Assumptions	Priced at Cost or Owner's Equity	[6]	Priced at Cost or Owner's Equity	[6]
Available-for-sale Securities, Equity Securities	$ 4.0		$ 4.0
Fair Value Measurements, Valuation Techniques	- Market Convention		- Market Convention

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

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

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

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

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

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

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