Investments - Change in Allowance for Credit Losses on Fixed Maturities Available-for-Sale (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	$ 8.2	$ 9.6
Additions for Securities for which No Previous Expected Credit Losses were Recognized	3.4	2.9
Reductions due to Sales	(0.8)	(2.6)
Net (Decrease) Increase in Allowance on Securities for which Expected Credit Losses were Previously Recognized	(0.1)	(0.9)
Write-offs Charged Against Allowance		(0.8)
Balance, End of Year	10.7	8.2
States and Political Subdivisions
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	0.5	0.7
Additions for Securities for which No Previous Expected Credit Losses were Recognized	0.0	0.0
Reductions due to Sales	0.0	0.0
Net (Decrease) Increase in Allowance on Securities for which Expected Credit Losses were Previously Recognized	0.2	(0.2)
Write-offs Charged Against Allowance		(0.4)
Balance, End of Year	0.3	0.5
Bonds and Notes
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	7.7	8.9
Additions for Securities for which No Previous Expected Credit Losses were Recognized	3.4	2.9
Reductions due to Sales	(0.8)	(2.6)
Net (Decrease) Increase in Allowance on Securities for which Expected Credit Losses were Previously Recognized	0.1	(1.1)
Write-offs Charged Against Allowance		(0.4)
Balance, End of Year	$ 10.4	$ 7.7