Significant business acquisitions - Summary of unaudited pro forma consolidated earnings (Detail) - Alleghany and PTC Acquisitions [Member] $ / shares in Units, $ in Millions	9 Months Ended
Sep. 30, 2022 USD ($) $ / shares
Business Acquisition [Line Items]
Revenues	$ 287,682
Net earnings (loss) attributable to Berkshire Hathaway shareholders	$ (41,161)
Common Class A [Member]
Business Acquisition [Line Items]
Net earnings (loss) per equivalent Class A common share \| $ / shares	$ (27,987)

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 805
-SubTopic 20
-Name Accounting Standards Codification
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The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-Section 50
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-Topic 805
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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
-Name Accounting Standards Codification
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-URI https://asc.fasb.org//1943274/2147479328/805-10-50-2

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