Fair Value of Financial Instruments - Quantitative Estimates for Level 3 Assets (Details) (USD $) In Millions, unless otherwise specified																									3 Months Ended		12 Months Ended		3 Months Ended		12 Months Ended		3 Months Ended		12 Months Ended		3 Months Ended		12 Months Ended		3 Months Ended		12 Months Ended		3 Months Ended		12 Months Ended		3 Months Ended		12 Months Ended		3 Months Ended		12 Months Ended		3 Months Ended		12 Months Ended		3 Months Ended													12 Months Ended	3 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended
	Mar. 31, 2014 US Treasury and Government Level 3		Dec. 31, 2013 US Treasury and Government Level 3		Mar. 31, 2014 State and political subdivision Level 3		Dec. 31, 2013 State and political subdivision Level 3		Mar. 31, 2014 Corporate Level 3		Dec. 31, 2013 Corporate Level 3		Mar. 31, 2014 Other asset-backed Level 3		Dec. 31, 2013 Other asset-backed Level 3		Mar. 31, 2014 Fair value investments Level 3		Dec. 31, 2013 Fair value investments Level 3		Mar. 31, 2014 EIA/VED Embedded Derivative Level 3	Dec. 31, 2013 EIA/VED Embedded Derivative Level 3	Mar. 31, 2014 GMAB/GMWB Embedded Derivatives Level 3	Dec. 31, 2013 GMAB/GMWB Embedded Derivatives Level 3	Mar. 31, 2014 Market Approach Valuation Technique [Member] US Treasury and Government		Dec. 31, 2012 Market Approach Valuation Technique [Member] US Treasury and Government		Mar. 31, 2014 Market Approach Valuation Technique [Member] US Treasury and Government Minimum		Dec. 31, 2012 Market Approach Valuation Technique [Member] US Treasury and Government Minimum		Mar. 31, 2014 Market Approach Valuation Technique [Member] US Treasury and Government Maximum		Dec. 31, 2012 Market Approach Valuation Technique [Member] US Treasury and Government Maximum		Mar. 31, 2014 Market Approach Valuation Technique [Member] State and political subdivision		Dec. 31, 2012 Market Approach Valuation Technique [Member] State and political subdivision		Mar. 31, 2014 Market Approach Valuation Technique [Member] State and political subdivision Minimum		Dec. 31, 2012 Market Approach Valuation Technique [Member] State and political subdivision Minimum		Mar. 31, 2014 Market Approach Valuation Technique [Member] State and political subdivision Maximum		Dec. 31, 2012 Market Approach Valuation Technique [Member] State and political subdivision Maximum		Mar. 31, 2014 Market Approach Valuation Technique [Member] Corporate		Dec. 31, 2012 Market Approach Valuation Technique [Member] Corporate		Mar. 31, 2014 Market Approach Valuation Technique [Member] Corporate Minimum		Dec. 31, 2012 Market Approach Valuation Technique [Member] Corporate Minimum		Mar. 31, 2014 Market Approach Valuation Technique [Member] Corporate Maximum		Dec. 31, 2012 Market Approach Valuation Technique [Member] Corporate Maximum		Mar. 31, 2014 Income Approach Valuation Technique Other asset-backed		Mar. 31, 2013 Income Approach Valuation Technique Other asset-backed		Mar. 31, 2014 Income Approach Valuation Technique Other asset-backed Minimum		Mar. 31, 2013 Income Approach Valuation Technique Other asset-backed Minimum		Mar. 31, 2014 Income Approach Valuation Technique Other asset-backed Maximum		Mar. 31, 2013 Income Approach Valuation Technique Other asset-backed Maximum		Mar. 31, 2014 Income Approach Valuation Technique EIA/VED Embedded Derivative Minimum Level 3	Dec. 31, 2012 Income Approach Valuation Technique EIA/VED Embedded Derivative Minimum Level 3	Mar. 31, 2014 Income Approach Valuation Technique EIA/VED Embedded Derivative Maximum Level 3	Dec. 31, 2013 Income Approach Valuation Technique EIA/VED Embedded Derivative Maximum Level 3	Dec. 31, 2012 Income Approach Valuation Technique EIA/VED Embedded Derivative Maximum Level 3	Mar. 31, 2014 Income Approach Valuation Technique GMAB/GMWB Embedded Derivatives Level 3	Dec. 31, 2012 Income Approach Valuation Technique GMAB/GMWB Embedded Derivatives Level 3	Mar. 31, 2014 Income Approach Valuation Technique GMAB/GMWB Embedded Derivatives Minimum Level 3	Dec. 31, 2012 Income Approach Valuation Technique GMAB/GMWB Embedded Derivatives Minimum Level 3	Mar. 31, 2014 Income Approach Valuation Technique GMAB/GMWB Embedded Derivatives Maximum Level 3	Dec. 31, 2012 Income Approach Valuation Technique GMAB/GMWB Embedded Derivatives Maximum Level 3	Mar. 31, 2014 Income Approach Valuation Technique Fair Value Investments		Mar. 31, 2013 Income Approach Valuation Technique Fair Value Investments
Fair Value, Option, Quantitative Disclosures [Line Items]
U.S. government and agency	$ 65.8	[1]	$ 58.8	[2]
State and political subdivision					46.4	[1]	45.4	[2]
Corporate									948.7	[1]	874.1	[2]
Other asset-backed													10.4	[1]	11.3	[2]	0.8	[1]	0.8	[2]
Yield																									3.17%	[1]	3.18%	[2]	0.95%	[1]	1.07%	[2]	6.29%	[1]	5.00%	[2]	3.86%	[1]	3.88%	[2]	2.36%	[1]	2.44%	[2]	5.33%	[1]	5.79%	[2]	3.63%	[1]	3.81%	[2]	0.95%	[1]	1.06%	[2]	6.29%	[1]	6.75%	[2]	2.12%	[1]	2.30%	[2]	1.90%	[1]	2.10%	[2]	3.32%	[1]	3.41%	[2]
Prepayment rate																																																															2.00%	[2]
Default rate																																																															2.53%	[2]																				0.26%	[1]	0.25%	[2]
Recovery rate																																																															10.00%	[2]																				42.00%	[1]	45.00%	[2]
Default rate term 2																																																															0.37%	[2]
Embedded derivatives																					$ 97.2	$ 78.9	$ (3.5)	$ (4.1)
Mortality rate																																																																									97.00%	97.00%	103.00%	103.00%		105.00%	105.00%
Lapse rate																																																																									0.02%	0.02%	35.00%		47.15%			0.00%	0.00%	40.00%	40.00%
Volatility surface																																																																																9.57%	10.85%	46.36%	46.33%
Swap curve																																																																									0.17%	0.19%	3.40%		3.79%			0.14%	0.15%	3.70%	4.15%

[1] Excludes Level 3 assets which are valued based upon non-binding independent third-party valuations or third-party price information for which unobservable inputs are not reasonably available to us.

[2] Excludes Level 3 assets which are valued based upon non-binding independent third-party valuations or third-party price information for which unobservable inputs are not reasonably available to us.