Reserve for Unpaid Losses and Loss Adjustment Expenses - Average Annual Payout of Incurred Claims by Age, P&C (Details)	Dec. 31, 2024
Workers' Compensation \| P&C Business Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1st Year	14.80%
2nd Year	18.40%
3rd Year	12.10%
4th Year	8.10%
5th Year	5.70%
6th Year	4.00%
7th Year	2.90%
8th Year	2.10%
9th Year	1.70%
10th Year	1.30%
General liability \| P&C Business Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1st Year	2.50%
2nd Year	7.80%
3rd Year	11.80%
4th Year	16.60%
5th Year	15.50%
6th Year	12.30%
7th Year	9.10%
8th Year	5.90%
9th Year	3.70%
10th Year	0.60%
Marine [Member] \| P&C Business Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1st Year	22.80%
2nd Year	32.00%
3rd Year	16.80%
4th Year	7.50%
5th Year	6.70%
6th Year	6.20%
7th Year	0.80%
8th Year	0.40%
9th Year	(1.50%)
10th Year	(0.70%)
Package Business [Member] \| P&C Business Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1st Year	35.80%
2nd Year	22.40%
3rd Year	9.60%
4th Year	9.30%
5th Year	6.40%
6th Year	4.30%
7th Year	3.30%
8th Year	2.10%
9th Year	1.40%
10th Year	1.20%
Property Insurance [Member] \| P&C Business Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1st Year	49.90%
2nd Year	31.90%
3rd Year	7.50%
4th Year	3.30%
5th Year	1.50%
6th Year	0.80%
7th Year	0.00%
8th Year	0.20%
9th Year	(0.20%)
10th Year	(0.50%)
Property Insurance [Member] \| P&C Personal Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1st Year	67.70%
2nd Year	26.20%
3rd Year	2.00%
4th Year	0.60%
5th Year	0.80%
6th Year	0.20%
7th Year	0.10%
8th Year	0.10%
9th Year	0.10%
10th Year	0.00%
Automobile liability \| P&C Business Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1st Year	14.10%
2nd Year	19.40%
3rd Year	20.10%
4th Year	17.00%
5th Year	12.20%
6th Year	6.80%
7th Year	4.20%
8th Year	1.20%
9th Year	0.70%
10th Year	0.00%
Automobile liability \| P&C Personal Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1st Year	32.70%
2nd Year	34.40%
3rd Year	16.30%
4th Year	8.00%
5th Year	3.60%
6th Year	1.40%
7th Year	0.60%
8th Year	0.20%
9th Year	0.20%
10th Year	0.10%
Commercial automobile physical damage \| P&C Business Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1st Year	78.20%
2nd Year	17.30%
3rd Year	(0.20%)
Professional liability \| P&C Business Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1st Year	5.30%
2nd Year	16.10%
3rd Year	16.50%
4th Year	11.80%
5th Year	9.60%
6th Year	10.30%
7th Year	8.90%
8th Year	3.40%
9th Year	2.40%
10th Year	(1.90%)
Surety Product Line [Member] \| P&C Business Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1st Year	11.10%
2nd Year	26.40%
3rd Year	11.00%
4th Year	8.60%
5th Year	1.20%
6th Year	(1.10%)
7th Year	(1.60%)
8th Year	(7.80%)
9th Year	(0.30%)
10th Year	(0.30%)
Assumed Reinsurance [Member] \| P&C Business Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1st Year	26.10%
2nd Year	33.00%
3rd Year	14.20%
4th Year	6.80%
5th Year	5.90%
6th Year	2.40%
7th Year	(1.00%)
8th Year	0.80%
9th Year	0.10%
10th Year	(0.40%)
Personal automobile physical damage \| P&C Personal Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1st Year	91.90%
2nd Year	6.30%
3rd Year	(0.40%)

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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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- 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.

+ References

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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.

+ References

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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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- Definition

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.

+ References

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- Definition

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.

+ References

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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.

+ References

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