Fair Value of Financial Instruments Fair Value of Financial Instruments - Quantitative Estimates for Level 3 Liabilities (Details) (Level 3, USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
EIA/VED Embedded Derivative
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Embedded derivatives	$ 63.4	$ 51.2
EIA/VED Embedded Derivative | Income Approach Valuation Technique
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Mortality rate	75.00%	75.00%
Fair Value Inputs, CSA Rate	3.76%	4.47%
EIA/VED Embedded Derivative | Minimum | Income Approach Valuation Technique
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Swap curve	0.24%	0.21%
Lapse rate	0.60%	1.00%
EIA/VED Embedded Derivative | Maximum | Income Approach Valuation Technique
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Swap curve	2.69%	2.50%
Lapse rate	35.00%	35.00%
GMAB/GMWB Embedded Derivatives
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Embedded derivatives	$ 18.4	$ 28.3
GMAB/GMWB Embedded Derivatives | Income Approach Valuation Technique
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Mortality rate	75.00%	75.00%
Fair Value Inputs, CSA Rate	3.76%	4.47%
GMAB/GMWB Embedded Derivatives | Minimum | Income Approach Valuation Technique
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Swap curve	0.24%	0.36%
Lapse rate	0.00%	0.00%
Volatility surface	9.32%	11.67%
GMAB/GMWB Embedded Derivatives | Maximum | Income Approach Valuation Technique
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Swap curve	3.18%	3.17%
Lapse rate	60.00%	60.00%
Volatility surface	44.45%	50.83%