Separate Accounts, Death Benefits and Other Insurance Benefit Features and Embedded Product Derivatives - GMDB and GMIB Benefits by Type (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Net Amount at Risk by Product and Guarantee [Line Items]
Account Value	$ 2,177.8	$ 2,232.4
NAR after Reinsurance	27.0	34.9
Average Attained Age of Annuitant	64 years	64 years
Less: General account value with GMDB	300.3	311.3
Subtotal separate account liabilities with GMDB	1,877.5	1,921.1
Separate account liabilities without GMDB	143.8	140.7
Total separate account liabilities	2,021.3	2,061.8
GMIB	390.9	403.3
GMDB return of premium [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Account Value	726.8	755.9
NAR after Reinsurance	3.2	5.7
Average Attained Age of Annuitant	62 years	62 years
GMDB step up [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Account Value	1,389.2	1,412.4
NAR after Reinsurance	17.2	21.7
Average Attained Age of Annuitant	63 years	62 years
GMDB earnings enhancement benefit (EEB) [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Account Value	36.1	37.4
NAR after Reinsurance	0.1	0.1
Average Attained Age of Annuitant	63 years	63 years
GMDB greater of annual step up and roll up [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Account Value	25.7	26.7
NAR after Reinsurance	$ 6.5	$ 7.4
Average Attained Age of Annuitant	67 years	67 years