Quantitative Information Regarding Significant Unobservable Inputs (Details) $ in Millions		Dec. 31, 2024 USD ($) Rate	Dec. 31, 2023 USD ($) Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed Maturity Securities		$ 35,629.9	$ 36,833.9
Equity Securities		24.5	31.9
All Other Corporate Bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed Maturity Securities		24,822.2	25,670.7
Mortgage/Asset-backed Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed Maturity Securities	[1]	917.2	644.1
Fair Value, Inputs, Level 3 | Market Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity Securities	[2]	24.4	21.6
Fair Value, Inputs, Level 3 | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Asset in Modified Coinsurance Arrangement	[3]	$ 11.5
Embedded Derivative Liability in Modified Coinsurance Arrangement	[3]		$ (1.5)
Fair Value, Inputs, Level 3 | Discounted Cash Flow | Weighted Average | Input Measurement, Spread of Swap Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Liability, Measurement Input | Rate			0.002
Embedded Derivative Asset, Measurement Input | Rate		(0.0023)
Fair Value, Inputs, Level 3 | All Other Corporate Bonds | Market Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed Maturity Securities	[2],[4]	$ 16.3	$ 15.9
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		0.0500	0.0500
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		0.0500	0.0500
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		0.0500	0.0500
Fair Value, Inputs, Level 3 | Mortgage/Asset-backed Securities | Market Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed Maturity Securities		$ 21.2

[1] 2Includes credit-tranched securities collateralized by loan obligations, auto loans, and other asset types

[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 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

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