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SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES (Details) $ in Millions	Dec. 31, 2025 USD ($)
Summary of investments other than investments in related parties
Cost or Amortized Cost	$ 7,478.3
Carrying Value	8,324.9
Fair Value	8,324.9
Fixed maturity investments
Summary of investments other than investments in related parties
Cost or Amortized Cost	2,774.8
Carrying Value	2,770.5
Fair Value	2,770.5
U.S. Government and agency obligations
Summary of investments other than investments in related parties
Cost or Amortized Cost	459.7
Carrying Value	460.3
Fair Value	460.3
Debt securities issued by corporations
Summary of investments other than investments in related parties
Cost or Amortized Cost	1,534.9
Carrying Value	1,537.7
Fair Value	1,537.7
Mortgage and asset-backed securities
Summary of investments other than investments in related parties
Cost or Amortized Cost	405.1
Carrying Value	393.0
Fair Value	393.0
Collateralized loan obligations
Summary of investments other than investments in related parties
Cost or Amortized Cost	343.9
Carrying Value	347.0
Fair Value	347.0
Foreign government and agency obligations
Summary of investments other than investments in related parties
Cost or Amortized Cost	31.2
Carrying Value	32.5
Fair Value	32.5
Short-term investments
Summary of investments other than investments in related parties
Cost or Amortized Cost	1,881.2
Carrying Value	1,881.7
Fair Value	1,881.7
Equity Method Investments
Summary of investments other than investments in related parties
Cost or Amortized Cost	1,727.3
Carrying Value	2,375.1
Equity Method Investments | MediaAlpha
Summary of investments other than investments in related parties
Cost or Amortized Cost	59.2
Carrying Value	231.2
Fair Value	231.2
Industrial, Miscellaneous and Other
Summary of investments other than investments in related parties
Cost or Amortized Cost	353.7
Carrying Value	452.3
Fair Value	452.3
Exchange-traded funds
Summary of investments other than investments in related parties
Cost or Amortized Cost	30.6
Carrying Value	30.7
Fair Value	30.7
Total common equity securities
Summary of investments other than investments in related parties
Cost or Amortized Cost	384.3
Carrying Value	483.0
Fair Value	483.0
Other long-term investments
Summary of investments other than investments in related parties
Cost or Amortized Cost	2,378.8
Carrying Value	2,958.5
Fair Value	$ 2,958.5

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Subsection 15
-Publisher SEC

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-7

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Amount of investment held by insurance company, excluding investment in related party.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15(Column D))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-7

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15(Column B))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-7

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15(Column C))
-Publisher FASB
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