Quantitative Information Regarding Significant Unobservable Inputs (Details) (Fair Value, Inputs, Level 3, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Embedded Derivative Liability
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs	(49.9)		(53.2)
Embedded Derivative Liability | Projected Cash Flows
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Significant Assumptions to Calculating Fair Value of Level 3 Instrument	Actuarial Assumptions	[1]	Actuarial Assumptions	[1]
States, Municipalities, and Political Subdivisions
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs	101.0		142.7
States, Municipalities, and Political Subdivisions | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Comparability Adjustments	0.25%	[2]	0.25%	[2]
States, Municipalities, and Political Subdivisions | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Comparability Adjustments	1.00%	[2]	1.25%	[2]
States, Municipalities, and Political Subdivisions | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Comparability Adjustments	0.71%	[2]	0.65%	[2]
Mortgage/Asset-backed Securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs			0.5
Mortgage/Asset-backed Securities | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Discount for Size			4.93%	[3]
Mortgage/Asset-backed Securities | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Discount for Size			5.03%	[3]
Mortgage/Asset-backed Securities | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Discount for Size			5.01%	[3]
All Other Corporate Bonds - Private
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs	432.8		371.3
All Other Corporate Bonds - Private | Market Convention
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Significant Assumptions to Calculating Fair Value of Level 3 Instrument	Priced at Par	[4]	Priced at Par	[4]
All Other Corporate Bonds - Private | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Change in Benchmark Reference			3.36%	[5]
Comparability Adjustments	0.50%	[2]	(0.70%)	[2]
Discount for Size	0.50%	[3]	0.50%	[3]
Lack of Marketability	0.48%	[6]	0.20%	[6]
Volatility of Credit	0.20%	[7]	0.07%	[7]
All Other Corporate Bonds - Private | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Change in Benchmark Reference			3.36%	[5]
Comparability Adjustments	0.70%	[2]	(0.40%)	[2]
Discount for Size	0.50%	[3]	0.50%	[3]
Lack of Marketability	0.48%	[6]	1.00%	[6]
Volatility of Credit	2.00%	[7]	4.00%	[7]
All Other Corporate Bonds - Private | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Change in Benchmark Reference			3.36%	[5]
Comparability Adjustments	0.60%	[2]	(0.60%)	[2]
Discount for Size	0.50%	[3]	0.50%	[3]
Lack of Marketability	0.48%	[6]	0.55%	[6]
Volatility of Credit	0.64%	[7]	0.85%	[7]
Corporate Bond Securities - Public
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs	128.7		514.4
Corporate Bond Securities - Public | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Change in Benchmark Reference			(0.32%)	[5]
Comparability Adjustments	0.10%	[2]	(0.23%)	[2]
Lack of Marketability	0.20%	[6]	0.20%	[6]
Volatility of Credit	(0.30%)	[7]	(0.88%)	[7]
Corporate Bond Securities - Public | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Change in Benchmark Reference			0.25%	[5]
Comparability Adjustments	0.50%	[2]	1.00%	[2]
Lack of Marketability	0.35%	[6]	0.20%	[6]
Volatility of Credit	0.50%	[7]	0.46%	[7]
Corporate Bond Securities - Public | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Change in Benchmark Reference			0.04%	[5]
Comparability Adjustments	0.40%	[2]	0.41%	[2]
Lack of Marketability	0.29%	[6]	0.20%	[6]
Volatility of Credit	(0.05%)	[7]	(0.26%)	[7]
Equity Securites
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs	1.1		4.2
Equity Securites | Market Convention
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Significant Assumptions to Calculating Fair Value of Level 3 Instrument	Priced at Cost or Owner's Equity	[4]	Priced at Cost or Owner's Equity	[4]

[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 based on issue/issuer size relative to the benchmark

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

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

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

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