Fair Value of Financial Instruments - Carrying Amounts and Fair Values (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Level 3 | Policy Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 69.2	$ 68.1
Fair Value	68.7	67.6
Level 3 | Investment Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	3,425.8	3,306.9
Fair Value	3,427.5	3,308.6
Level 3 | Reported Value Measurement | Surplus Notes | Surplus Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Surplus notes	30.0	30.0
Level 1 | Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	93.9	162.3
Fair Value	$ 93.9	$ 162.3