Significant business acquisitions and other transactions - Summary of unaudited pro forma consolidated earnings (Detail) - Alleghany and PTC Acquisitions [Member] $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2022 USD ($) $ / shares
Business Acquisition [Line Items]
Revenues	$ 383,115
Net earnings (loss) attributable to Berkshire shareholders	$ (23,947)
Common Class A [Member]
Business Acquisition [Line Items]
Net earnings (loss) per equivalent Class A common share \| $ / shares	$ (16,303)

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
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+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-Section 50
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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