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Unpaid losses and loss adjustment expenses - Average historical claims duration (Detail) - Insurance Group [Member] | Dec. 31, 2023
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GEICO [Member] | Physical Damage [Member] |
Shortduration Insurance Contracts Historical Claims Duration [Line Items] |
Average annual percentage payout of incurred losses, net of reinsurance, year one | 97.00%
Average annual percentage payout of incurred losses, net of reinsurance, year two | 3.00%
GEICO [Member] | Auto Liability [Member] |
Shortduration Insurance Contracts Historical Claims Duration [Line Items] |
Average annual percentage payout of incurred losses, net of reinsurance, year one | 41.00%
Average annual percentage payout of incurred losses, net of reinsurance, year two | 31.00%
Average annual percentage payout of incurred losses, net of reinsurance, year three | 13.00%
Average annual percentage payout of incurred losses, net of reinsurance, year four | 7.00%
Average annual percentage payout of incurred losses, net of reinsurance, year five | 4.00%
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] |
Shortduration Insurance Contracts Historical Claims Duration [Line Items] |
Average annual percentage payout of incurred losses, net of reinsurance, year one | 2.00%
Average annual percentage payout of incurred losses, net of reinsurance, year two | 8.00%
Average annual percentage payout of incurred losses, net of reinsurance, year three | 12.00%
Average annual percentage payout of incurred losses, net of reinsurance, year four | 14.00%
Average annual percentage payout of incurred losses, net of reinsurance, year five | 13.00%
Average annual percentage payout of incurred losses, net of reinsurance, year six | 12.00%
Average annual percentage payout of incurred losses, net of reinsurance, year seven | 8.00%
Average annual percentage payout of incurred losses, net of reinsurance, year eight | 6.00%
Average annual percentage payout of incurred losses, net of reinsurance, year nine | 5.00%
Average annual percentage payout of incurred losses, net of reinsurance, year ten | 3.00%
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] |
Shortduration Insurance Contracts Historical Claims Duration [Line Items] |
Average annual percentage payout of incurred losses, net of reinsurance, year one | 15.00%
Average annual percentage payout of incurred losses, net of reinsurance, year two | 18.00%
Average annual percentage payout of incurred losses, net of reinsurance, year three | 14.00%
Average annual percentage payout of incurred losses, net of reinsurance, year four | 13.00%
Average annual percentage payout of incurred losses, net of reinsurance, year five | 9.00%
Average annual percentage payout of incurred losses, net of reinsurance, year six | 6.00%
Average annual percentage payout of incurred losses, net of reinsurance, year seven | 5.00%
Average annual percentage payout of incurred losses, net of reinsurance, year eight | 3.00%
Average annual percentage payout of incurred losses, net of reinsurance, year nine | 1.00%
Average annual percentage payout of incurred losses, net of reinsurance, year ten | 2.00%
Berkshire Hathaway Reinsurance Group [Member] | Property [Member] |
Shortduration Insurance Contracts Historical Claims Duration [Line Items] |
Average annual percentage payout of incurred losses, net of reinsurance, year one | 22.00%
Average annual percentage payout of incurred losses, net of reinsurance, year two | 35.00%
Average annual percentage payout of incurred losses, net of reinsurance, year three | 15.00%
Average annual percentage payout of incurred losses, net of reinsurance, year four | 8.00%
Average annual percentage payout of incurred losses, net of reinsurance, year five | 4.00%
Average annual percentage payout of incurred losses, net of reinsurance, year six | 4.00%
Average annual percentage payout of incurred losses, net of reinsurance, year seven | 2.00%
Average annual percentage payout of incurred losses, net of reinsurance, year eight | 2.00%
Average annual percentage payout of incurred losses, net of reinsurance, year nine | 2.00%
Average annual percentage payout of incurred losses, net of reinsurance, year ten | 1.00%
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] |
Shortduration Insurance Contracts Historical Claims Duration [Line Items] |
Average annual percentage payout of incurred losses, net of reinsurance, year one | 14.00%
Average annual percentage payout of incurred losses, net of reinsurance, year two | 17.00%
Average annual percentage payout of incurred losses, net of reinsurance, year three | 13.00%
Average annual percentage payout of incurred losses, net of reinsurance, year four | 11.00%
Average annual percentage payout of incurred losses, net of reinsurance, year five | 8.00%
Average annual percentage payout of incurred losses, net of reinsurance, year six | 6.00%
Average annual percentage payout of incurred losses, net of reinsurance, year seven | 5.00%
Average annual percentage payout of incurred losses, net of reinsurance, year eight | 4.00%
Average annual percentage payout of incurred losses, net of reinsurance, year nine | 3.00%
Average annual percentage payout of incurred losses, net of reinsurance, year ten | 2.00%

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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://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 4G -SubTopic 40 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-4G + 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 -Name Accounting Standards Codification -Section 50 -Paragraph 4G -SubTopic 40 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-4G + Details
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- Definition 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 Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 4G -SubTopic 40 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-4G + Details
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- Definition 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 Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 4G -SubTopic 40 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-4G + Details
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- Definition 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 Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 4G -SubTopic 40 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-4G + Details
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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 Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 4G -SubTopic 40 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-4G + Details
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