Credit Losses (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Credit Loss [Abstract]
Premium Receivable, Allowance for Credit Loss	$ 10.3	$ 10.8	$ 4.6
Premium Receivable, Allowance for Credit Loss, Period Increase (Decrease)	10.6	13.0
Premium Receivable, Allowance for Credit Loss, Writeoff	(2.5)	(6.8)
Premium Receivable, Allowance for Credit Loss, Recovery	(8.6)	0.0
Reinsurance Recoverable, Allowance for Credit Loss	0.6	0.4	0.0
Reinsurance Recoverable, Allowance for Credit Loss, Period Increase (Decrease)	0.2	0.4
Debt Securities, Available-for-sale, Allowance for Credit Loss	0.2	0.7	$ 0.0
Debt Securities, Available-for-sale, Allowance for Credit Loss, Period Increase (Decrease)	0.0	3.1
Debt Securities, Available-for-sale, Allowance for Credit Loss, Securities Sold	(0.2)	(2.4)
Debt Securities, Available-for-sale, Allowance for Credit Loss, Recovery	(0.3)	0.0
Accrued investment income	$ 14.5	$ 15.3

Interest, dividends, rents, ancillary and other revenues earned but not yet received by the entity on its investments.

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Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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The carrying value as of the balance sheet date of the estimated valuation allowance to reduce gross premiums receivable to net realizable value.

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