Quantitative Information Regarding Significant Unobservable Inputs (Details) (Fair Value, Inputs, Level 3, USD $) In Millions, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2013		Dec. 31, 2012
Embedded Derivative in Modified Coinsurance Arrangement
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Embedded Derivative in Modified Coinsurance Arrangement	$ (65.1)		$ (83.9)
Fair Value Measurements, Valuation Techniques	- Projected Liability Cash Flows		- Projected Liability Cash Flows
Embedded Derivative in Modified Coinsurance Arrangement | Projected Cash Flows
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Significant Assumptions	Actuarial Assumptions	[1]	Actuarial Assumptions	[1]
States, Municipalities, and Political Subdivisions
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value of fixed maturity securities	117.9		42.7
Fair Value Measurements, Valuation Techniques	- Comparability Adjustment		- Comparability Adjustment - Lack of Marketability - Volatility of Credit
States, Municipalities, and Political Subdivisions | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	0.25%	[2]	0.25%	[2]
Volatility of Credit			0.15%	[3]
Lack of Marketability			0.25%	[4]
States, Municipalities, and Political Subdivisions | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	1.25%	[2]	0.25%	[2]
Volatility of Credit			0.15%	[3]
Lack of Marketability			0.25%	[4]
States, Municipalities, and Political Subdivisions | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	0.67%	[2]	0.25%	[2]
Volatility of Credit			0.15%	[3]
Lack of Marketability			0.25%	[4]
Public Utilities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value of fixed maturity securities	68.1		17.4
Fair Value Measurements, Valuation Techniques	- Volatility of Credit		- Comparability Adjustment
Public Utilities | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments			0.20%	[2]
Volatility of Credit	0.25%	[3]
Public Utilities | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments			0.20%	[2]
Volatility of Credit	0.75%	[3]
Public Utilities | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments			0.20%	[2]
Volatility of Credit	0.42%	[3]
Mortgage/Asset-backed Securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value of fixed maturity securities	0.5		0.5
Fair Value Measurements, Valuation Techniques	- Discount for Size		- Discount for Size
Mortgage/Asset-backed Securities | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount for Size	5.24%	[5]	5.74%	[5]
Mortgage/Asset-backed Securities | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount for Size	5.36%	[5]	5.84%	[5]
Mortgage/Asset-backed Securities | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount for Size	5.32%	[5]	5.81%	[5]
All Other Corporate Bonds - Private
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value of fixed maturity securities	229.6		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
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Significant Assumptions	Priced at Par	[6]	Priced at Par	[6]
All Other Corporate Bonds - Private | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	(0.40%)	[2]	1.48%	[2]
Volatility of Credit	(0.72%)	[3]	(0.25%)	[3]
Discount for Size	0.50%	[5]	0.10%	[5]
Change in Benchmark Reference	2.16%	[7]	0.04%	[7]
Lack of Marketability	1.00%	[4]	0.10%	[4]
All Other Corporate Bonds - Private | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	(0.40%)	[2]	1.48%	[2]
Volatility of Credit	4.00%	[3]	7.72%	[3]
Discount for Size	0.50%	[5]	0.50%	[5]
Change in Benchmark Reference	2.16%	[7]	2.89%	[7]
Lack of Marketability	1.00%	[4]	1.00%	[4]
All Other Corporate Bonds - Private | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	(0.40%)	[2]	1.48%	[2]
Volatility of Credit	0.92%	[3]	1.51%	[3]
Discount for Size	0.50%	[5]	0.24%	[5]
Change in Benchmark Reference	2.16%	[7]	0.28%	[7]
Lack of Marketability	1.00%	[4]	0.46%	[4]
Corporate Bond Securities - Public
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value of fixed maturity securities	216.2		165.0
Fair Value Measurements, Valuation Techniques	- Change in Benchmark Reference - Comparability Adjustment - 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
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Significant Assumptions			Priced at Par	[6]
Corporate Bond Securities - Public | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	(0.45%)	[2]	(0.59%)	[2]
Volatility of Credit	(0.46%)	[3]	(0.30%)	[3]
Discount for Size			0.25%	[5]
Change in Benchmark Reference	(1.11%)	[7]	0.25%	[7]
Lack of Marketability	0.20%	[4]	0.20%	[4]
Corporate Bond Securities - Public | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	1.00%	[2]	1.00%	[2]
Volatility of Credit	(0.12%)	[3]	(0.30%)	[3]
Discount for Size			0.25%	[5]
Change in Benchmark Reference	0.35%	[7]	0.25%	[7]
Lack of Marketability	0.20%	[4]	0.30%	[4]
Corporate Bond Securities - Public | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	0.17%	[2]	0.27%	[2]
Volatility of Credit	(0.29%)	[3]	(0.30%)	[3]
Discount for Size			0.25%	[5]
Change in Benchmark Reference	(0.27%)	[7]	0.25%	[7]
Lack of Marketability	0.20%	[4]	0.24%	[4]
Equity Securites
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value of Equity Securities - Private	$ 4.0		$ 4.0
Fair Value Measurements, Valuation Techniques	- Market Convention		- Market Convention
Equity Securites | Market Convention
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Significant Assumptions	Priced at Cost or Owner's Equity	[6]	Priced at Cost or Owner's Equity	[6]

[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