Investments - Net Investment Income (Parenthetical) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Net Investment Income, Reported Amounts, by Category [Line Items]
Investment, Type [Extensible Enumeration]	Deposit Asset Underlying10 Insurance Agreement [Member]	Deposit Asset Underlying10 Insurance Agreement [Member]	Deposit Asset Underlying10 Insurance Agreement [Member]
Gains (Losses) recognized for change in fair value of deposit asset underlying the 10% coinsurance agreement	$ (0.4)	$ (3.8)	$ (2.5)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Realized Investment Gains (Losses)	Realized Investment Gains (Losses)	Realized Investment Gains (Losses)
Percentage of coinsurance costs	10.00%	10.00%	10.00%