Reserves For Losses And Loss Expenses (Supplementary Information Regarding Average Historical Claims Duration) (Details)	Dec. 31, 2024
Insurance \| Other liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 1	5.70%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 2	13.20%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 3	15.80%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 4	16.20%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 5	13.20%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 6	10.60%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 7	8.60%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 8	6.50%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 9	5.00%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 10	3.10%
Insurance \| Workers' compensation
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 1	24.70%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 2	31.10%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 3	16.30%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 4	9.10%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 5	5.20%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 6	3.50%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 7	2.50%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 8	2.00%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 9	1.10%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 10	0.90%
Insurance \| Professional liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 1	7.30%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 2	16.00%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 3	16.30%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 4	14.80%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 5	9.00%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 6	10.10%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 7	6.70%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 8	3.10%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 9	3.20%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 10	2.50%
Insurance \| Auto
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 1	33.70%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 2	20.40%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 3	14.80%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 4	12.10%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 5	8.20%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 6	4.20%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 7	2.20%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 8	1.40%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 9	0.50%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 10	0.50%
Insurance \| Short-tail lines
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 1	53.10%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 2	33.60%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 3	6.20%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 4	2.80%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 5	0.70%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 6	0.80%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 7	0.50%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 8	0.30%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 9	0.80%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 10	0.20%
Reinsurance & Monoline Excess \| Casualty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 1	6.30%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 2	11.00%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 3	12.70%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 4	14.50%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 5	11.70%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 6	11.20%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 7	9.00%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 8	7.10%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 9	4.30%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 10	3.80%
Reinsurance & Monoline Excess \| Monoline excess
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 1	7.30%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 2	5.10%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 3	3.30%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 4	2.70%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 5	3.10%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 6	2.60%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 7	2.70%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 8	3.60%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 9	3.70%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 10	2.00%
Reinsurance & Monoline Excess \| Property
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 1	34.40%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 2	32.10%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 3	15.10%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 4	5.60%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 5	3.70%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 6	1.50%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 7	1.20%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 8	0.70%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 9	0.40%
Average annual percentage payout of incurred claims by age, net of reinsurance, Year 10	0.30%

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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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- Definition

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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