Fair Value of Financial Instruments Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Ceded Policy Loans	$ 3,066.5		$ 3,066.5		$ 3,150.1
Long-term Debt	3,042.6		3,042.6		2,449.4
Gain (Loss) on Embedded Derivative	10.2	$ (2.0)	4.6	$ (5.9)
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term Debt	$ 2,444.4		$ 2,444.4		956.4
Percentage of Total Fair Value of Fixed Maturities Securities	21.90%		21.90%
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term Debt	$ 889.4		$ 889.4		$ 1,689.5
Fair Value, Inputs, Level 2 | Pricing Service
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Percentage of Total Fair Value of Fixed Maturities Securities	63.60%		63.60%
Fair Value, Inputs, Level 2 | Other Observable Market Data
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Percentage of Total Fair Value of Fixed Maturities Securities	3.00%		3.00%
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Private Equity Partnership Future Liquidation Term			1 year
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Private Equity Partnership Future Liquidation Term			11 years
Fair Value Inputs Other Than Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Percentage of Total Fair Value of Fixed Maturities Securities	78.10%		78.10%
Fair Value Inputs Level 2 Or Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Percentage of Total Fair Value of Fixed Maturities Securities	11.50%		11.50%