Investments - Schedule of Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 0.9	$ 0.2
Securities for which allowance was not previously recorded	0.2	0.1
Additional net increases (decreases) in existing allowance	0.1	(0.1)
Ending balance	1.2	0.2
Foreign Governments
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance		0.2
Securities for which allowance was not previously recorded		0.0
Additional net increases (decreases) in existing allowance		(0.2)
Ending balance		0.0
Corporate bonds
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance	0.9	0.0
Securities for which allowance was not previously recorded	0.1	0.1
Additional net increases (decreases) in existing allowance	0.1	0.1
Ending balance	1.1	$ 0.2
Asset-backed securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance	0.0
Securities for which allowance was not previously recorded	0.1
Additional net increases (decreases) in existing allowance	0.0
Ending balance	$ 0.1

Debt Securities, Available-for-sale, Excluding Accrued Interest, Allowance for Credit Loss, Additional Period Increase (Decrease)

No definition available.

+ 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 excluding accrued interest, 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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

+ Details

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- Definition

Amount, excluding accrued interest, of credit loss expense on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) with no credit loss previously recorded.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479106/326-30-50-9

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- Details

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- Details

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