Fair Value of Financial Instruments Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Ceded Policy Loans	$ 3,270.8	$ 3,313.6
Derivative Credit Risk Valuation Adjustment, Derivative Assets	0.0	0.0
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	$ 0.0	$ 0.0
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Percentage of Total Fair Value of Fixed Maturities Securities	20.20%
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	61.90%
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	17.10%
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	79.80%
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	0.80%