Fair value measurements - Significant unobservable inputs (Detail) (Significant Unobservable Inputs (Level 3) [Member], USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011
Net Derivative Contract Liabilities [Member]
Fair value measurements Significant unobservable inputs [Line Items]
Beginning Balance	$ (9,908)	$ (8,222)
Gains (losses) included in earnings	23	194
Gains (losses) included in other comprehensive income	3
Gains (losses) included in regulatory assets and liabilities	3	83
Settlements	13	(23)
Ending Balance	(9,866)	(7,968)
Fixed Maturities [Member]
Fair value measurements Significant unobservable inputs [Line Items]
Beginning Balance	784	801
Gains (losses) included in other comprehensive income	5	3
Acquisitions		6
Dispositions	(7)	(33)
Transfers out of Level 3	(129)
Ending Balance	653	777
Equity Securities [Member]
Fair value measurements Significant unobservable inputs [Line Items]
Beginning Balance	22	35
Gains (losses) included in other comprehensive income	16	5
Ending Balance	38	40
Other Fixed Maturities and Equity Securities [Member]
Fair value measurements Significant unobservable inputs [Line Items]
Beginning Balance	11,669	17,589
Gains (losses) included in other comprehensive income	1,770	(1,385)
Transfers out of Level 3		(5,500)
Ending Balance	$ 13,439	$ 10,704

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Namespace Prefix:	brka_
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Balance Type:	na
Period Type:	duration

This element represents dispositions which have taken place during the period in relation to assets and liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3).

+ References

No definition available.

+ Details

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Namespace Prefix:	brka_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents amounts recorded to regulatory assets and liabilities arising from net derivative contract liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3).

+ References

No definition available.

+ Details

Name:	brka_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisRegulatoryAssetsAndLiabilities
Namespace Prefix:	brka_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of gain (loss) recognized in earnings, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of gain (loss) recognized in other comprehensive income, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Purchases that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Settlements that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Transfers out of assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant