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Investment Securities - Debt Securities Issued by Corporation (Details) - Debt securities issued by corporations - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Debt Securities, Trading, Credit Quality Indicator [Line Items]
Fixed maturity investments, at fair value	$ 1,104.5	$ 1,045.0
AAA
Debt Securities, Trading, Credit Quality Indicator [Line Items]
Fixed maturity investments, at fair value	14.1	11.5
AA
Debt Securities, Trading, Credit Quality Indicator [Line Items]
Fixed maturity investments, at fair value	83.7	83.8
A
Debt Securities, Trading, Credit Quality Indicator [Line Items]
Fixed maturity investments, at fair value	552.7	552.4
BBB
Debt Securities, Trading, Credit Quality Indicator [Line Items]
Fixed maturity investments, at fair value	445.3	390.9
BB
Debt Securities, Trading, Credit Quality Indicator [Line Items]
Fixed maturity investments, at fair value	2.0	0.0
Other
Debt Securities, Trading, Credit Quality Indicator [Line Items]
Fixed maturity investments, at fair value	$ 6.7	$ 6.4

X

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
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Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
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-URI https://asc.fasb.org/1943274/2147483467/210-10-45-1

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- Definition

Debt Securities, Trading, Credit Quality Indicator

+ References

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