Fair Value of Financial Instruments - Carrying Amounts and Fair Values (Details) - Level 3 - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Reported Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Policy loans	$ 70.7	$ 68.1
Investment contracts	3,554.6	3,306.9
Reported Value Measurement | Surplus Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Surplus notes	30.0	30.0
Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Policy loans	70.2	67.6
Investment contracts	3,555.5	3,308.6
Estimate of Fair Value Measurement | Surplus Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Surplus notes	$ 30.0	$ 30.0