Allowance for Credit Losses - Premiums Receivable (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Credit Loss [Abstract]
Premiums receivable	$ 271.1	$ 292.0	$ 648.6
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, December 31, 2022	4.7	5.7
Current period change for estimated uncollectible premiums	0.4	0.2
Write-offs of uncollectible premiums receivable	0.0	(1.2)
Balance, March 31, 2023	$ 5.1	$ 4.7