Fair Value of Financial Instruments - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) security	Dec. 31, 2022 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of investment portfolio fair value pricing services or index price	87.70%	88.60%
Net investment losses included in net income related to financial assets	$ (0.4)	$ 3.4
Net investment (gains) losses included in net income related to financial liabilities	$ (1.3)	14.8
Fair Value Recurring Basis Unobservable Input Reconciliation Liability Gain Loss Statement Of Income Extensible List Not Disclosed Flag	true
Carrying Value | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Separate account (variable annuity) assets	$ 3,294.1	2,792.3
Fair Value | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Separate account (variable annuity) assets	$ 3,294.1	2,792.3
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of invested assets in total investment portfolio Level 3 recurring	9.50%
Fair Value, Inputs, Level 3 | Fair Value | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Separate account (variable annuity) assets	$ 0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Fair Value | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Separate account (variable annuity) assets	3,294.1	2,792.3
Fair Value, Inputs, Level 2 [Member] | Fair Value | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Separate account (variable annuity) assets	$ 0.0	$ 0.0
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of hard-to-value fixed maturity securities | security	75
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of hard-to-value fixed maturity securities | security	125