Fair Value of Financial Instruments - Carrying Amounts and Fair Values (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Level 3 | Policy Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 62.8	$ 61.0
Fair Value	62.4	60.6
Level 3 | Investment Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	2,566.5	2,349.8
Fair Value	2,569.5	2,355.4
Level 1 | Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	123.9	83.1
Fair Value	$ 123.9	$ 83.1