Quantitative Information Regarding Significant Unobservable Inputs (Details) (Fair Value, Inputs, Level 3, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Embedded Derivative in Modified Coinsurance Arrangement
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Quantitative unobservable inputs Level 3 fair value - internally derived	$ (53.2)		$ (83.9)
States, Municipalities, and Political Subdivisions
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Quantitative unobservable inputs Level 3 fair value - internally derived	142.7		42.7
States, Municipalities, and Political Subdivisions | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	0.25%	[1]	0.25%	[1]
Volatility of Credit			0.15%	[2]
Lack of Marketability			0.25%	[3]
States, Municipalities, and Political Subdivisions | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	1.25%	[1]	0.25%	[1]
Volatility of Credit			0.15%	[2]
Lack of Marketability			0.25%	[3]
States, Municipalities, and Political Subdivisions | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	0.65%	[1]	0.25%	[1]
Volatility of Credit			0.15%	[2]
Lack of Marketability			0.25%	[3]
Public Utilities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Quantitative unobservable inputs Level 3 fair value - internally derived	64.3		17.4
Public Utilities | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments			0.20%	[1]
Volatility of Credit	0.75%	[2]
Public Utilities | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments			0.20%	[1]
Volatility of Credit	1.25%	[2]
Public Utilities | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments			0.20%	[1]
Volatility of Credit	0.92%	[2]
Mortgage/Asset-backed Securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Quantitative unobservable inputs Level 3 fair value - internally derived	0.5		0.5
Mortgage/Asset-backed Securities | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount for Size	4.93%	[4]	5.74%	[4]
Mortgage/Asset-backed Securities | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount for Size	5.03%	[4]	5.84%	[4]
Mortgage/Asset-backed Securities | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Discount for Size	5.01%	[4]	5.81%	[4]
All Other Corporate Bonds - Private
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Quantitative unobservable inputs Level 3 fair value - internally derived	307.0		391.8
All Other Corporate Bonds - Private | Market Convention
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Significant Assumptions to Calculating Fair Value of Level 3 Instrument	Priced at Par	[5]	Priced at Par	[5]
All Other Corporate Bonds - Private | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	(0.70%)	[1]	1.48%	[1]
Volatility of Credit	0.07%	[2]	(0.25%)	[2]
Discount for Size	0.50%	[4]	0.10%	[4]
Change in Benchmark Reference	3.36%	[6]	0.04%	[6]
Lack of Marketability	0.20%	[3]	0.10%	[3]
All Other Corporate Bonds - Private | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	(0.40%)	[1]	1.48%	[1]
Volatility of Credit	4.00%	[2]	7.72%	[2]
Discount for Size	0.50%	[4]	0.50%	[4]
Change in Benchmark Reference	3.36%	[6]	2.89%	[6]
Lack of Marketability	1.00%	[3]	1.00%	[3]
All Other Corporate Bonds - Private | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	(0.60%)	[1]	1.48%	[1]
Volatility of Credit	0.84%	[2]	1.51%	[2]
Discount for Size	0.50%	[4]	0.24%	[4]
Change in Benchmark Reference	3.36%	[6]	0.28%	[6]
Lack of Marketability	0.55%	[3]	0.46%	[3]
Corporate Bond Securities - Public
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Quantitative unobservable inputs Level 3 fair value - internally derived	514.4		165.0
Corporate Bond Securities - Public | Market Convention
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Significant Assumptions to Calculating Fair Value of Level 3 Instrument			Priced at Par	[5]
Corporate Bond Securities - Public | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	(0.23%)	[1]	(0.59%)	[1]
Volatility of Credit	(0.88%)	[2]	(0.30%)	[2]
Discount for Size			0.25%	[4]
Change in Benchmark Reference	(0.32%)	[6]	0.25%	[6]
Lack of Marketability	0.20%	[3]	0.20%	[3]
Corporate Bond Securities - Public | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	1.00%	[1]	1.00%	[1]
Volatility of Credit	0.46%	[2]	(0.30%)	[2]
Discount for Size			0.25%	[4]
Change in Benchmark Reference	0.25%	[6]	0.25%	[6]
Lack of Marketability	0.20%	[3]	0.30%	[3]
Corporate Bond Securities - Public | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Comparability Adjustments	0.41%	[1]	0.27%	[1]
Volatility of Credit	(0.26%)	[2]	(0.30%)	[2]
Discount for Size			0.25%	[4]
Change in Benchmark Reference	0.04%	[6]	0.25%	[6]
Lack of Marketability	0.20%	[3]	0.24%	[3]
Equity Securites
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Quantitative unobservable inputs Level 3 fair value - internally derived	$ 4.2		$ 4.0
Equity Securites | Market Convention
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Significant Assumptions to Calculating Fair Value of Level 3 Instrument	Priced at Cost or Owner's Equity	[5]	Priced at Cost or Owner's Equity	[5]
Embedded Derivative in Modified Coinsurance Arrangement | Projected Cash Flows
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Significant Assumptions to Calculating Fair Value of Level 3 Instrument	Actuarial Assumptions	[7]	Actuarial Assumptions	[7]

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

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

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

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

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

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

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