Fair Value Measurements - Quantitative Information for Level 3 Inputs (Details) - Market Yield - Significant Unobservable Inputs (Level 3) $ in Millions	Mar. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Senior Debt | Measurement Input, Discount Rate | Non-investment-grade | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt instrument, measurement input	0.067	0.070
Senior Debt | Measurement Input, Discount Rate | Non-investment-grade | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt instrument, measurement input	0.266	0.241
Senior Debt | Measurement Input, Discount Rate | Non-investment-grade | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt instrument, measurement input	0.104	0.100
Junior Debt | Measurement Input, Discount Rate | Non-investment-grade | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt instrument, measurement input	0.084	0.095
Junior Debt | Measurement Input, Discount Rate | Non-investment-grade | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt instrument, measurement input	0.270	0.310
Junior Debt | Measurement Input, Discount Rate | Non-investment-grade | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt instrument, measurement input	0.125	0.132
Investment-grade | Investment grade
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 74.4	$ 59.9
Investment-grade | Measurement Input, Discount Rate | Investment grade | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Alternative investment, measurement input	0.016	0.034
Investment-grade | Measurement Input, Discount Rate | Investment grade | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Alternative investment, measurement input	0.094	0.116
Investment-grade | Measurement Input, Discount Rate | Investment grade | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Alternative investment, measurement input	0.073	0.079
Senior Debt | Non-investment-grade
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 114.9	$ 42.7
Junior Debt | Non-investment-grade
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	31.3	35.7
Other
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	150.7	66.9
Investments in Fixed Maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Assets, Fair Value Disclosure	$ 371.3	$ 205.2