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Retroactive reinsurance contracts - Narrative (Detail) - USD ($) $ in Billions | Mar. 31, 2024 | Dec. 31, 2023
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Retroactive Reinsurance [Member] |  |
Effects of Reinsurance [Line Items] |  |
Unamortized deferred charges of retroactive reinsurance contracts | $ 9.3 | $ 9.5

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- Definition The remaining unamortized excess of the estimated ultimate liability for claims and claim costs over the premiums earned with respect to retroactive property/casualty reinsurance contracts. + References No definition available. + Details
Name: | brka_UnamortizedDeferredChargesOnReinsuranceAssumed
Namespace Prefix: | brka_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_EffectsOfReinsuranceLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_CededCreditRiskAxis=brka_RetroactiveReinsuranceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |