Separate Accounts, Death Benefits and Other Insurance Benefit Features and Embedded Product Derivatives - Corporate Account Investments of Account Balances of Variable Annuity Contracts with Guarantees (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Insurance [Abstract]
Debt securities	$ 356.6	$ 369.3
Equity funds	1,571.6	1,516.3
Other	47.7	49.7
Total	$ 1,975.9	$ 1,935.3