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, 2013	Dec. 31, 2012
Variable Annuity Embedded Derivatives Table [Line Items]
GMWB	$ 10.1	$ 14.3
Average Attained Age of Annuitant	64 years	64 years
GMAB	8.6	14.3
COMBO	(0.3)	(0.3)
Total variable annuity embedded derivative liabilities	18.4	28.3
Account Value
Variable Annuity Embedded Derivatives Table [Line Items]
GMWB	564.5	547.4
GMAB	389.3	379.5
COMBO	8.0	8.3
Total variable annuity embedded derivative liabilities	$ 961.8	$ 935.2
GMWB
Variable Annuity Embedded Derivatives Table [Line Items]
Average Attained Age of Annuitant	63 years	63 years
GMAB
Variable Annuity Embedded Derivatives Table [Line Items]
Average Attained Age of Annuitant	58 years	58 years
COMBO
Variable Annuity Embedded Derivatives Table [Line Items]
Average Attained Age of Annuitant	61 years	61 years