RESERVES FOR LOSSES AND LOSS SETTLEMENT EXPENSES - Average Historical Claims Duration (Details)	Dec. 31, 2025
Commercial other liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	7.10%
Year 2	14.10%
Year 3	14.10%
Year 4	16.50%
Year 5	10.20%
Year 6	9.00%
Year 7	8.10%
Year 8	5.60%
Year 9	4.40%
Year 10	9.40%
Commercial fire and allied
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	58.60%
Year 2	22.00%
Year 3	6.90%
Year 4	3.90%
Year 5	2.70%
Year 6	1.40%
Year 7	0.40%
Year 8	0.00%
Year 9	0.40%
Year 10	0.00%
Commercial automobile
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	35.70%
Year 2	21.30%
Year 3	17.30%
Year 4	11.80%
Year 5	7.80%
Year 6	3.20%
Year 7	1.60%
Year 8	0.40%
Year 9	0.50%
Year 10	0.00%
Commercial workers' compensation
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	34.40%
Year 2	31.70%
Year 3	13.80%
Year 4	8.20%
Year 5	4.10%
Year 6	2.50%
Year 7	1.50%
Year 8	1.10%
Year 9	0.10%
Year 10	0.40%
Personal
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	51.30%
Year 2	35.20%
Year 3	13.80%
Year 4	2.20%
Year 5	0.60%
Year 6	0.30%
Year 7	0.50%
Year 8	0.10%
Year 9	0.40%
Year 10	0.00%

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- Definition

Percentage of average annual payout, after reinsurance, in the eighth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 55
-Paragraph 9F
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480046/944-40-55-9F

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 4G
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480081/944-40-50-4G

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Percentage of average annual payout, after reinsurance, in the fifth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the fourth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

+ References

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Percentage of average annual payout, after reinsurance, in the ninth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

+ References

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Percentage of average annual payout, after reinsurance, in the first year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the seventh year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the sixth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the tenth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the third year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the second year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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