Investments - Allowance for Credit Loss Impairments on Fixed Maturity Securities (Details) - Fixed maturity securities - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 1.2	$ 1.2	$ 7.7
Credit losses on fixed maturity securities for which credit losses were not previously reported	1.7	0.0	0.0
Net increases (decreases) related to credit losses previously reported	(0.4)	0.0	3.1
Reduction of credit allowances related to sales	(1.6)	0.0	(9.2)
Write-offs	0.0	0.0	(0.4)
Ending balance	$ 0.9	$ 1.2	$ 1.2