Fair Value of Financial Instruments - Fair Value by Balance Sheet Grouping (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	$ 61.5	$ 61.0
Fair Value	61.1	60.6
Level 3 | Investment Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	2,468.1	2,349.8
Fair Value	2,472.7	2,355.4
Level 1 | Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	116.2	83.1
Fair Value	$ 116.2	$ 83.1