Significant business acquisitions - Pro forma consolidated earnings data (Detail) (NV Energy, IMI plc and LSPI [Member], USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013
NV Energy, IMI plc and LSPI [Member]
Business Acquisition [Line Items]
Revenues	$ 44,685
Net earnings attributable to Berkshire Hathaway shareholders	$ 4,924
Net earnings per equivalent Class A common share attributable to Berkshire Hathaway shareholders	$ 2,997

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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/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

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- Definition

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

+ Details

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- Definition

The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

+ References

+ Details

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