Fair Value of Financial Instruments - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities at fair value	$ 99.6	$ 147.2
Derivatives embedded in fixed indexed annuity products	91.0
Fair Value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities at fair value	99.6	147.2
Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives embedded in fixed indexed annuity products	91.0
Fair Value, Inputs, Level 3 | Fair Value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities at fair value	$ 2.0	1.4
discounted cash flow | Fair Value, Inputs, Level 3 | lapse rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives embedded in fixed indexed annuity products, measurement input	0.054
discounted cash flow | Fair Value, Inputs, Level 3 | Mortality multiplier
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives embedded in fixed indexed annuity products, measurement input	0.678
discounted cash flow | Fair Value, Inputs, Level 3 | non-performance adjustment
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives embedded in fixed indexed annuity products, measurement input	5
market comparable | Fair Value, Inputs, Level 3 | price/book ExAOCI
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities, measurement input	1.06
black-scholes | Fair Value, Inputs, Level 3 | time to exit
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities, measurement input	2.67
Minimum | discounted cash flow | Fair Value, Inputs, Level 3 | option budget
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives embedded in fixed indexed annuity products, measurement input	0.0090
Minimum | black-scholes | Fair Value, Inputs, Level 3 | volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities, measurement input	0.280
Maximum | discounted cash flow | Fair Value, Inputs, Level 3 | option budget
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives embedded in fixed indexed annuity products, measurement input	0.0340
Maximum | black-scholes | Fair Value, Inputs, Level 3 | volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities, measurement input	0.440
Municipal bonds | Fair Value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value		1,703.4
Municipal bonds | Fair Value, Inputs, Level 3 | Fair Value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 54.4	60.8
Municipal bonds | Minimum | discounted cash flow | Fair Value, Inputs, Level 3 | option adjusted spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0308
Corporate bonds | Fair Value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value		2,388.7
Corporate bonds | Fair Value, Inputs, Level 3 | Fair Value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 261.3	$ 210.3
Corporate bonds | discounted cash flow | Fair Value, Inputs, Level 3 | option adjusted spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	241
Corporate bonds | discounted cash flow | Fair Value, Inputs, Level 3 | exit cap rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.062
Corporate bonds | vendor priced | Fair Value, Inputs, Level 3 | vendor priced
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.00796
Corporate bonds | market comparable | Fair Value, Inputs, Level 3 | EV / Fwd EBITDA (x)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	5.92
Corporate bonds | Minimum | discounted cash flow | Fair Value, Inputs, Level 3 | yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.061
Corporate bonds | Minimum | discounted cash flow | Fair Value, Inputs, Level 3 | discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.062
Corporate bonds | Maximum | discounted cash flow | Fair Value, Inputs, Level 3 | yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.110
Corporate bonds | Maximum | discounted cash flow | Fair Value, Inputs, Level 3 | discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.107
Mortgage-backed and other asset-backed securities | Fair Value, Inputs, Level 3 | Fair Value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 107.6
Mortgage-backed and other asset-backed securities | discounted cash flow | Fair Value, Inputs, Level 3 | London Interbank Offered Rate (LIBOR)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.023
Mortgage-backed and other asset-backed securities | discounted cash flow | Fair Value, Inputs, Level 3 | discount margin
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.395
Mortgage-backed and other asset-backed securities | discounted cash flow | Fair Value, Inputs, Level 3 | PDI spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.055
Mortgage-backed and other asset-backed securities | discounted cash flow | Fair Value, Inputs, Level 3 | SBL spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.045
Mortgage-backed and other asset-backed securities | discounted cash flow | Fair Value, Inputs, Level 3 | CPR
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.200
Mortgage-backed and other asset-backed securities | discounted cash flow | Fair Value, Inputs, Level 3 | default rate annual
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.040
Mortgage-backed and other asset-backed securities | discounted cash flow | Fair Value, Inputs, Level 3 | recovery
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.650
Mortgage-backed and other asset-backed securities | discounted cash flow | Fair Value, Inputs, Level 3 | I spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0175
Mortgage-backed and other asset-backed securities | discounted cash flow | Fair Value, Inputs, Level 3 | N spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0463
Mortgage-backed and other asset-backed securities | discounted cash flow | Fair Value, Inputs, Level 3 | T spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0226
Mortgage-backed and other asset-backed securities | market comparable | Fair Value, Inputs, Level 3 | median price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	81.34
Mortgage-backed and other asset-backed securities | Minimum | discounted cash flow | Fair Value, Inputs, Level 3 | yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.064
Mortgage-backed and other asset-backed securities | Minimum | discounted cash flow | Fair Value, Inputs, Level 3 | discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.160
Mortgage-backed and other asset-backed securities | Minimum | discounted cash flow | Fair Value, Inputs, Level 3 | median comparable yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.207
Mortgage-backed and other asset-backed securities | Minimum | discounted cash flow | Fair Value, Inputs, Level 3 | weighting
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.170
Mortgage-backed and other asset-backed securities | Minimum | vendor priced | Fair Value, Inputs, Level 3 | haircut
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0001
Mortgage-backed and other asset-backed securities | Maximum | discounted cash flow | Fair Value, Inputs, Level 3 | yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.065
Mortgage-backed and other asset-backed securities | Maximum | discounted cash flow | Fair Value, Inputs, Level 3 | discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.210
Mortgage-backed and other asset-backed securities | Maximum | discounted cash flow | Fair Value, Inputs, Level 3 | median comparable yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.432
Mortgage-backed and other asset-backed securities | Maximum | discounted cash flow | Fair Value, Inputs, Level 3 | weighting
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.830
Mortgage-backed and other asset-backed securities | Maximum | vendor priced | Fair Value, Inputs, Level 3 | haircut
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.003