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
	Sep. 30, 2013		Dec. 31, 2012
Net Amount at Risk by Product and Guarantee [Line Items]
Account Value	$ 2,200.5		$ 2,232.4
NAR after Reinsurance	16.8		34.9
Average Attained Age of Annuitant	64 years		64 years
Less: General account value with GMDB	299.1		311.3
Subtotal separate account liabilities with GMDB	1,901.4		1,921.1
Separate account liabilities without GMDB	148.1		140.7
Total separate account liabilities	2,049.5		2,061.8
GMIB	388.5	[1]	403.3	[1]
GMDB return of premium [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Account Value	732.4		755.9
NAR after Reinsurance	2.3		5.7
Average Attained Age of Annuitant	63 years		62 years
GMDB step up [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Account Value	1,405.6		1,412.4
NAR after Reinsurance	8.8		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	35.8		37.4
NAR after Reinsurance	0.1		0.1
Average Attained Age of Annuitant	64 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	26.7		26.7
NAR after Reinsurance	$ 5.6		$ 7.4
Average Attained Age of Annuitant	67 years		67 years

[1] Policies with a GMIB also have a GMDB, however these benefits are not additive. When a policy terminates due to death, any NAR related to GMIB is released. Similarly, when a policy goes into benefit status on a GMIB, its GMDB NAR is released.