Investments- Allowance for Credit Loss Impairments on Fixed Maturity Securities (Details) - Fixed maturity securities - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale, Allowance for Credit Loss
Beginning balance	$ 1.2	$ 8.3	$ 1.2	$ 7.7
Credit losses on fixed maturity securities for which credit losses were not previously reported	0.0	0.0
Net increase related to credit losses previously reported	0.0	0.9
Reduction of credit allowances related to sales	0.0	0.0
Write-offs	0.0	(0.3)
Ending balance	$ 1.2	$ 8.3