Allowance for Credit Losses - Reinsurance Recoverables (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance recoverables, net	$ 3,029.1	$ 2,966.4	$ 3,009.0
Balance, December 31, 2021	3.8	4.1
Current period change for estimated uncollectible reinsurance	1.7	(0.3)
Write-offs of uncollectible reinsurance recoverables	0.0	0.0
Reclassified to assets held-for-sale	(0.8)
Balance, December 31, 2022	$ 4.7	$ 3.8

Reinsurance Recoverable, Allowance for Credit Loss, Reclassified to Assets Held-for-Sale

No definition available.

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Balance Type:	credit
Period Type:	duration

- Definition

Amount of the write-down or write-off of a receivable from a reinsurer.

+ References

+ Details

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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- Definition

Amount of expense (reversal of expense) for expected credit loss on reinsurance recoverable.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Amount, after valuation allowance, recoverable under reinsurance contracts including premium paid under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(6))
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 50
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-URI https://asc.fasb.org/extlink&oid=99397103&loc=d3e6824-158387

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 5
-URI https://asc.fasb.org/extlink&oid=99404803&loc=d3e21409-158489

+ Details

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Period Type:	instant

- Definition

Amount of allowance for credit loss on reinsurance recoverable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

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-Publisher FASB
-Name Accounting Standards Codification
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

+ Details

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Balance Type:	credit
Period Type:	instant