Derivative contracts - Narrative (Detail) - USD ($)	9 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Finance and Financial Products [Member]
Derivative [Line Items]
Liabilities	$ 4,430,000,000	$ 4,810,000,000
Finance and Financial Products [Member] \| Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Collateral posting requirements under contracts with collateral provisions	0	0
Additional collateral posting requirements	1,100,000,000
Liabilities	4,430,000,000	4,810,000,000
Finance and Financial Products [Member] \| Not Designated as Hedging Instrument [Member] \| Equity Index Put Options [Member]
Derivative [Line Items]
Aggregate intrinsic value of equity index put option contracts	$ 1,400,000,000	1,400,000,000
Weighted average remaining life of derivative contract	5 years 2 months 12 days
Liabilities	$ 4,188,000,000	4,560,000,000
Finance and Financial Products [Member] \| Not Designated as Hedging Instrument [Member] \| Credit Default Contracts - Municipalities [Member]
Derivative [Line Items]
Weighted average remaining life of derivative contract	16 years
Railroad, Utilities and Energy [Member] \| Not Designated as Hedging Instrument [Member] \| Other Assets [Member]
Derivative [Line Items]
Assets	$ 109,000,000	108,000,000
Railroad, Utilities and Energy [Member] \| Not Designated as Hedging Instrument [Member] \| Accounts Payable, Accruals and Other Liabilities [Member]
Derivative [Line Items]
Liabilities	$ 257,000,000	$ 230,000,000
Minimum [Member] \| Finance and Financial Products [Member] \| Not Designated as Hedging Instrument [Member] \| Equity Index Put Options [Member]
Derivative [Line Items]
Derivative maturity month and year	2018-06
Minimum [Member] \| Finance and Financial Products [Member] \| Not Designated as Hedging Instrument [Member] \| Credit Default Contracts - Municipalities [Member]
Derivative [Line Items]
Derivative maturity year	2019
Maximum [Member] \| Finance and Financial Products [Member] \| Not Designated as Hedging Instrument [Member] \| Equity Index Put Options [Member]
Derivative [Line Items]
Derivative maturity month and year	2026-01
Maximum [Member] \| Finance and Financial Products [Member] \| Not Designated as Hedging Instrument [Member] \| Credit Default Contracts - Municipalities [Member]
Derivative [Line Items]
Derivative maturity year	2054

Month and year the derivative contract matures, in YYYY-MM format.

No definition available.

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Namespace Prefix:	brka_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Year the derivative contract matures, in CCYY format.

+ References

No definition available.

+ Details

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

- Definition

Represents the undiscounted liability assuming the contracts are settled on their future expiration dates based on the index values at the most recent balance sheet date.

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4H

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624258-113959

+ Details

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Period Type:	instant

- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4H

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624258-113959

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- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13433-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13495-108611

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

+ Details

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Period Type:	instant

- Definition

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13495-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13433-108611

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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- Details

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- Details

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