Separate Accounts, Death Benefits and Other Insurance Benefit Features and Embedded Product Derivatives Variable Annuity GMDB Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Net Amount at Risk by Product and Guarantee [Line Items]
Account Value	$ 1,879.1	$ 2,192.4
Net Amount at Risk by Product and Guarantee, Net Amount at Risk, Before Reinsurance	71.9	73.4
NAR after Reinsurance	16.8	13.7
Average Attained Age of Annuitant	65 years	64 years
Less: General account value with GMDB	270.7	294.7
Subtotal separate account liabilities with GMDB	1,608.4	1,897.7
Separate account liabilities without GMDB	149.1	155.0
Total separate account liabilities	1,757.5	2,052.7
GMIB ending balance	308.4	385.7
Return of premium
Net Amount at Risk by Product and Guarantee [Line Items]
Account Value	626.6	728.8
Net Amount at Risk by Product and Guarantee, Net Amount at Risk, Before Reinsurance	1.4	1.8
NAR after Reinsurance	1.4	1.8
Average Attained Age of Annuitant	63 years	63 years
Step up
Net Amount at Risk by Product and Guarantee [Line Items]
Account Value	1,200.7	1,401.0
Net Amount at Risk by Product and Guarantee, Net Amount at Risk, Before Reinsurance	65.7	66.7
NAR after Reinsurance	10.6	7.0
Average Attained Age of Annuitant	64 years	63 years
Earnings enhancement benefit ("EEB")
Net Amount at Risk by Product and Guarantee [Line Items]
Account Value	29.1	35.9
Net Amount at Risk by Product and Guarantee, Net Amount at Risk, Before Reinsurance	0	0.1
NAR after Reinsurance	0	0.1
Average Attained Age of Annuitant	65 years	64 years
Greater of annual step up and roll up
Net Amount at Risk by Product and Guarantee [Line Items]
Account Value	22.7	26.7
Net Amount at Risk by Product and Guarantee, Net Amount at Risk, Before Reinsurance	4.8	4.8
NAR after Reinsurance	$ 4.8	$ 4.8
Average Attained Age of Annuitant	69 years	68 years