Investments- Allowance for Credit Loss Impairments on Fixed Maturity Securities (Details) - Fixed maturity securities - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Debt Securities, Available-for-sale, Allowance for Credit Loss
Beginning balance	$ 1.1	$ 1.2	$ 1.2	$ 1.2
Credit losses on fixed maturity securities for which credit losses were not previously reported	0.0	0.0	1.7	0.5
Net increase related to credit losses previously reported	0.5	0.0	(0.4)	0.0
Reduction of credit allowances related to sales	0.0	0.0	(0.9)	0.0
Write-offs	0.0	0.0	0.0	(0.5)
Ending balance	$ 1.6	$ 1.2	$ 1.6	$ 1.2