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, 2015	Dec. 31, 2014
Insurance [Abstract]
Debt securities	$ 265.5	$ 276.0
Equity funds	1,264.6	1,303.1
Other	35.1	35.5
Total	$ 1,565.2	$ 1,614.6