Quantitative Information Regarding Significant Unobservable Inputs (Details) $ in Millions		Mar. 31, 2023 USD ($) Rate	Dec. 31, 2022 USD ($) Rate	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity Securities		$ 26.5	$ 25.8
Embedded Derivative in Modified Coinsurance Arrangement
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs		(13.6)	(13.9)	$ (33.5)	$ (30.1)
Fair Value, Inputs, Level 3 | Discounted Cash Flow | Embedded Derivative in Modified Coinsurance Arrangement
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative in Modified Coinsurance Arrangement	[1]	$ (13.6)	$ (13.9)
Fair Value, Inputs, Level 3 | Discounted Cash Flow | Embedded Derivative in Modified Coinsurance Arrangement | Weighted Average | Input Measurement, Spread of Swap Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Liability, Measurement Input | Rate		0.006	0.006
Fair Value, Inputs, Level 3 | All Other Corporate Bonds | Market Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
All Other Corporate Bonds - Private	[2],[3]	$ 16.8	$ 15.3
Fair Value, Inputs, Level 3 | All Other Corporate Bonds | Market Approach | Minimum | Volatility of Credit
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
All Other Corporate Bonds - Private, Measurement Input | Rate		0.0462	0.0541
Fair Value, Inputs, Level 3 | All Other Corporate Bonds | Market Approach | Maximum | Volatility of Credit
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
All Other Corporate Bonds - Private, Measurement Input | Rate		0.0462	0.0541
Fair Value, Inputs, Level 3 | All Other Corporate Bonds | Market Approach | Weighted Average | Volatility of Credit
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
All Other Corporate Bonds - Private, Measurement Input | Rate		0.0462	0.0541
Fair Value, Inputs, Level 3 | Equity Securities | Market Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity Securities	[2]	$ 16.2	$ 16.2

[1] Represents various actuarial assumptions required to derive the liability cash flows. Fair value of embedded derivative is most often driven by the change in the weighted average credit spread to the swap curve for the assets backing the hypothetical loan

[2] Represents a decision to price based on par value, cost, owner's equity, or the price of the most recent capital funding round when limited data is available

[3] Represents basis point adjustments for credit-specific factors