Fair Value Measurements - Quantitative Information about Significant Unobservable Inputs (Details) - Valuation, Market Approach - Significant Unobservable Inputs (Level 3) $ in Millions	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Other
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Fair Value	$ 56.4	$ 32.0
Total Level 3 Fixed Maturity Investments
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Fair Value	227.9	249.9
Investment-grade | Investment-grade
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Fair Value	56.5	87.9
Non-investment-grade | Senior Debt
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Fair Value	72.9	76.1
Non-investment-grade | Junior Debt
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Fair Value	$ 42.1	$ 53.9
Measurement Input, Discount Rate | Investment-grade | Investment-grade | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Alternative investment, measurement input	0.046	0.023
Measurement Input, Discount Rate | Investment-grade | Investment-grade | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Alternative investment, measurement input	0.145	0.103
Measurement Input, Discount Rate | Investment-grade | Investment-grade | Weighted-average Yield
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Alternative investment, measurement input	0.092	0.054
Senior Debt | Measurement Input, Discount Rate | Non-investment-grade | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt instrument, measurement input	0.046	0.051
Senior Debt | Measurement Input, Discount Rate | Non-investment-grade | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt instrument, measurement input	0.367	0.202
Senior Debt | Measurement Input, Discount Rate | Non-investment-grade | Weighted-average Yield
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt instrument, measurement input	0.109	0.085
Junior Debt | Measurement Input, Discount Rate | Non-investment-grade | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt instrument, measurement input	0.088	0.060
Junior Debt | Measurement Input, Discount Rate | Non-investment-grade | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt instrument, measurement input	0.225	0.275
Junior Debt | Measurement Input, Discount Rate | Non-investment-grade | Weighted-average Yield
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt instrument, measurement input	0.151	0.150