Fair Value OF Financial Instrument - Quantitative Information about Significant Unobservable Inputs for Level 3 Recurring Fair Value Measurements (Details) $ in Millions	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Fair Value Measurement Inputs and Valuation Techniques
Fair Value	$ 5,714.6	$ 5,387.9
Net MRBs	(9.0)	(6.8)	$ (3.9)
Fair Value
Fair Value Measurement Inputs and Valuation Techniques
Fair Value	5,714.6	5,387.9
Fair Value | Corporate  Bonds
Fair Value Measurement Inputs and Valuation Techniques
Fair Value	$ 1,910.3	$ 1,782.4
Fair Value, Inputs, Level 3 | discounted cash flow | lapse rate | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques
Derivatives embedded in fixed indexed annuity products, measurement input	0.075	0.064
Net MRBs, measurement input	0.075	0.064
Fair Value, Inputs, Level 3 | discounted cash flow | mortality multiplier | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques
Derivatives embedded in fixed indexed annuity products, measurement input	0.710	0.670
Net MRBs, measurement input	0.710	0.670
Fair Value, Inputs, Level 3 | discounted cash flow | option budget | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Derivatives embedded in fixed indexed annuity products, measurement input	0.009	0.009
Fair Value, Inputs, Level 3 | discounted cash flow | option budget | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Derivatives embedded in fixed indexed annuity products, measurement input	0.039	0.038
Fair Value, Inputs, Level 3 | discounted cash flow | non-performance adjustment | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques
Derivatives embedded in fixed indexed annuity products, measurement input	0.050	0.050
Fair Value, Inputs, Level 3 | Corporate  Bonds | discounted cash flow | yield | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Corporate bonds, measurement input		0.039
Fair Value, Inputs, Level 3 | Corporate  Bonds | discounted cash flow | yield | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Corporate bonds, measurement input		0.106
Fair Value, Inputs, Level 3 | Corporate  Bonds | discounted cash flow | option adjusted spread | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Corporate bonds, measurement input		0.0242
Fair Value, Inputs, Level 3 | Corporate  Bonds | discounted cash flow | option adjusted spread | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Corporate bonds, measurement input		0.0768
Fair Value, Inputs, Level 3 | Fair Value
Fair Value Measurement Inputs and Valuation Techniques
Fair Value	$ 465.3	$ 499.9
Derivatives embedded in fixed indexed annuity products	82.1	82.3
Net MRBs	(9.0)	(6.8)
Fair Value, Inputs, Level 3 | Fair Value | Internal
Fair Value Measurement Inputs and Valuation Techniques
Fair Value	6.7	199.3
Fair Value, Inputs, Level 3 | Fair Value | Corporate  Bonds
Fair Value Measurement Inputs and Valuation Techniques
Fair Value	342.6	351.3
Fair Value, Inputs, Level 3 | Fair Value | Corporate  Bonds | Internal
Fair Value Measurement Inputs and Valuation Techniques
Fair Value	$ 6.7	$ 199.3