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

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