Separate Accounts, Death Benefits and Other Insurance Benefit Features and Embedded Product Derivatives - Non-Insurance Guaranteed Product Features(Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Variable Annuity Embedded Derivatives Table [Line Items]
GMWB	$ 9.0	$ 6.9
GMAB	(0.7)	(0.3)
COMBO	(0.1)	(0.2)
Total variable annuity embedded derivative liabilities	8.2	6.4
Average Attained Age of Annuitant	65 years	65 years
Account Value
Variable Annuity Embedded Derivatives Table [Line Items]
GMWB	453.6	471.3
GMAB	290.9	305.8
COMBO	5.2	6.9
Total variable annuity embedded derivative liabilities	$ 749.7	$ 784.0
GMWB
Variable Annuity Embedded Derivatives Table [Line Items]
Average Attained Age of Annuitant	65 years	65 years
GMAB
Variable Annuity Embedded Derivatives Table [Line Items]
Average Attained Age of Annuitant	59 years	59 years
COMBO
Variable Annuity Embedded Derivatives Table [Line Items]
Average Attained Age of Annuitant	63 years	64 years