Reserve for Loss and Loss Expense - Schedule of Short-duration Insurance Contracts, Schedule of Historical Claims Duration (Details)	Dec. 31, 2024
Standard Commercial Lines \| General liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration insurance contracts, Historical claims duration, year one	5.80%
Short-duration insurance contracts, historical claims duration, year two	11.00%
Short-duration insurance contracts, historical claims duration, year three	14.00%
Short-duration insurance contracts, historical claims duration, year four	16.20%
Short-duration insurance contracts, historical claims duration, year five	14.10%
Short-duration insurance contracts, historical claims duration, year six	10.30%
Short-duration insurance contracts, historical claims duration, year seven	8.90%
Short-duration insurance contracts, historical claims duration, year eight	5.00%
Short-duration insurance contracts, historical claims duration, year nine	3.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year ten	1.30%
Standard Commercial Lines \| Workers Compensation
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration insurance contracts, Historical claims duration, year one	23.30%
Short-duration insurance contracts, historical claims duration, year two	27.20%
Short-duration insurance contracts, historical claims duration, year three	13.10%
Short-duration insurance contracts, historical claims duration, year four	8.40%
Short-duration insurance contracts, historical claims duration, year five	4.10%
Short-duration insurance contracts, historical claims duration, year six	2.90%
Short-duration insurance contracts, historical claims duration, year seven	2.40%
Short-duration insurance contracts, historical claims duration, year eight	1.40%
Short-duration insurance contracts, historical claims duration, year nine	0.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year ten	0.70%
Standard Commercial Lines \| Commercial automobile
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration insurance contracts, Historical claims duration, year one	36.40%
Short-duration insurance contracts, historical claims duration, year two	18.00%
Short-duration insurance contracts, historical claims duration, year three	14.30%
Short-duration insurance contracts, historical claims duration, year four	12.40%
Short-duration insurance contracts, historical claims duration, year five	9.60%
Short-duration insurance contracts, historical claims duration, year six	4.30%
Short-duration insurance contracts, historical claims duration, year seven	2.10%
Short-duration insurance contracts, historical claims duration, year eight	1.10%
Short-duration insurance contracts, historical claims duration, year nine	0.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year ten	0.30%
Standard Commercial Lines \| Businessowners’ policies
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration insurance contracts, Historical claims duration, year one	49.50%
Short-duration insurance contracts, historical claims duration, year two	22.00%
Short-duration insurance contracts, historical claims duration, year three	8.20%
Short-duration insurance contracts, historical claims duration, year four	8.40%
Short-duration insurance contracts, historical claims duration, year five	5.90%
Short-duration insurance contracts, historical claims duration, year six	1.90%
Short-duration insurance contracts, historical claims duration, year seven	1.90%
Short-duration insurance contracts, historical claims duration, year eight	1.00%
Short-duration insurance contracts, historical claims duration, year nine	0.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year ten	0.20%
Standard Commercial Lines \| Commercial property
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration insurance contracts, Historical claims duration, year one	68.30%
Short-duration insurance contracts, historical claims duration, year two	26.80%
Short-duration insurance contracts, historical claims duration, year three	3.10%
Short-duration insurance contracts, historical claims duration, year four	0.80%
Short-duration insurance contracts, historical claims duration, year five	0.30%
Short-duration insurance contracts, historical claims duration, year six	0.20%
Short-duration insurance contracts, historical claims duration, year seven	0.10%
Short-duration insurance contracts, historical claims duration, year eight	0.10%
Short-duration insurance contracts, historical claims duration, year nine	0.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year ten	0.10%
Standard Personal Lines \| Personal automobile
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration insurance contracts, Historical claims duration, year one	58.80%
Short-duration insurance contracts, historical claims duration, year two	19.20%
Short-duration insurance contracts, historical claims duration, year three	9.20%
Short-duration insurance contracts, historical claims duration, year four	6.10%
Short-duration insurance contracts, historical claims duration, year five	3.50%
Short-duration insurance contracts, historical claims duration, year six	1.60%
Short-duration insurance contracts, historical claims duration, year seven	0.40%
Short-duration insurance contracts, historical claims duration, year eight	0.80%
Short-duration insurance contracts, historical claims duration, year nine	0.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year ten	0.10%
Standard Personal Lines \| Homeowners
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration insurance contracts, Historical claims duration, year one	71.20%
Short-duration insurance contracts, historical claims duration, year two	22.90%
Short-duration insurance contracts, historical claims duration, year three	3.30%
Short-duration insurance contracts, historical claims duration, year four	1.10%
Short-duration insurance contracts, historical claims duration, year five	1.00%
Short-duration insurance contracts, historical claims duration, year six	0.20%
Short-duration insurance contracts, historical claims duration, year seven	0.10%
Short-duration insurance contracts, historical claims duration, year eight	0.10%
Short-duration insurance contracts, historical claims duration, year nine	0.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year ten	0.10%
E&S Lines \| Casualty lines
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration insurance contracts, Historical claims duration, year one	3.60%
Short-duration insurance contracts, historical claims duration, year two	11.00%
Short-duration insurance contracts, historical claims duration, year three	17.20%
Short-duration insurance contracts, historical claims duration, year four	19.30%
Short-duration insurance contracts, historical claims duration, year five	14.90%
Short-duration insurance contracts, historical claims duration, year six	8.20%
Short-duration insurance contracts, historical claims duration, year seven	8.40%
Short-duration insurance contracts, historical claims duration, year eight	8.10%
Short-duration insurance contracts, historical claims duration, year nine	2.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year ten	1.80%

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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.

+ References

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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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