Quantitative Information Regarding Significant Unobservable Inputs (Details) $ in Millions		Jun. 30, 2022 USD ($) Rate	Dec. 31, 2021 USD ($) Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed Maturity Securities		$ 36,576.4	$ 43,336.0
Equity Securities		37.0	33.7
Public Utilities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed Maturity Securities		5,388.4	6,416.0
Corporate Debt Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed Maturity Securities		25,287.9	29,823.4
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		$ (34.3)	$ (30.1)
Fair Value, Inputs, Level 3 | Discounted Cash Flow | Embedded Derivative in Modified Coinsurance Arrangement | Weighted Average | Spread of Swap Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Embedded Derivative Liability, Measurement Input | Rate		0.010	0.007
Fair Value, Inputs, Level 3 | Public Utilities | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed Maturity Securities		$ 13.6
Fair Value, Inputs, Level 3 | Corporate Debt Securities | Market Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
All Other Corporate Bonds - Private		$ 11.1	$ 111.8
Fair Value, Inputs, Level 3 | Corporate Debt Securities | Market Approach | Minimum | Lack of Marketability
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
All Other Corporate Bonds - Private, Measurement Input | Rate	[1]		0.0014
Fair Value, Inputs, Level 3 | Corporate Debt Securities | Market Approach | Minimum | Volatility of Credit
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
All Other Corporate Bonds - Private, Measurement Input | Rate	[2]	0.0486	0.0630
Fair Value, Inputs, Level 3 | Corporate Debt Securities | Market Approach | Maximum | Lack of Marketability
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
All Other Corporate Bonds - Private, Measurement Input | Rate	[1]		0.0073
Fair Value, Inputs, Level 3 | Corporate Debt Securities | Market Approach | Maximum | Volatility of Credit
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
All Other Corporate Bonds - Private, Measurement Input | Rate	[2]	0.0486	0.0630
Fair Value, Inputs, Level 3 | Corporate Debt Securities | Market Approach | Weighted Average | Lack of Marketability
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
All Other Corporate Bonds - Private, Measurement Input | Rate	[1]		0.0051
Fair Value, Inputs, Level 3 | Corporate Debt Securities | Market Approach | Weighted Average | Volatility of Credit
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
All Other Corporate Bonds - Private, Measurement Input | Rate	[2]	0.0486	0.0630
Fair Value, Inputs, Level 3 | Equity Securities | Market Approach
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity Securities		$ 10.9	$ 5.8

[1] Represents basis point adjustments to apply a discount due to the illiquidity of an investment

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