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Liability for Losses and Loss Expenses - Supplementary Information About Average Historical Claims Duration (Detail) | Dec. 31, 2019
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Personal Automobile [Member] |
Claims Development [Line Items] |
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 1 | 64.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 2 | 17.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 3 | 8.80%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 4 | 4.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 5 | 2.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 6 | 0.90%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 7 | 0.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 8 | 0.30%
Homeowners [Member] |
Claims Development [Line Items] |
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 1 | 81.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 2 | 15.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 3 | 1.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 4 | 0.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 5 | 0.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 6 | 0.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 7 | 0.10%
Commercial Automobile [Member] |
Claims Development [Line Items] |
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 1 | 44.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 2 | 18.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 3 | 13.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 4 | 11.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 5 | 6.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 6 | 2.50%
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 | 0.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 9 | 0.70%
Commercial MultiPeril [Member] |
Claims Development [Line Items] |
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 1 | 47.80%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 2 | 17.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 3 | 10.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 4 | 10.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 5 | 6.60%
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 | 1.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 8 | 1.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 9 | 0.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 10 | 0.70%
Workers Compensation [Member] |
Claims Development [Line Items] |
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 1 | 29.90%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 2 | 31.50%
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 | 8.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 5 | 4.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 6 | 2.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 7 | 1.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 8 | 0.80%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year 9 | 0.70%

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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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4G -URI http://asc.fasb.org/extlink&oid=116884468&loc=SL65671329-158438 + Details
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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 Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4G -URI http://asc.fasb.org/extlink&oid=116884468&loc=SL65671329-158438 + Details
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