Business acquisition, contingent acquisition description.

No definition available.

Name:	brka_BusinessAcquisitionContingentAcquisitionDescription
Namespace Prefix:	brka_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Business acquisition, length of pipelines acquired.

+ References

No definition available.

+ Details

Name:	brka_BusinessAcquisitionLengthOfPipelinesAcquired
Namespace Prefix:	brka_
Data Type:	num:lengthItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investments acquired at the acquisition date.

+ References

No definition available.

+ Details

Name:	brka_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInvestments
Namespace Prefix:	brka_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unpaid losses and loss adjustment expenses acquired at the acquisition date.

+ References

No definition available.

+ Details

Name:	brka_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilityForClaimsAndClaimsAdjustmentExpense
Namespace Prefix:	brka_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Natural gas storage capacity acquired

+ References

No definition available.

+ Details

Name:	brka_NaturalGasStorageCapacityAcquired
Namespace Prefix:	brka_
Data Type:	num:energyItemType
Balance Type:	na
Period Type:	duration

- Definition

Payments to acquire businesses, net of post-closing adjustments.

+ References

No definition available.

+ Details

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

- Definition

Date when the business acquisition agreement was executed, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

Name:	us-gaap_BusinessAcquisitionDateOfAcquisitionAgreement1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Date when the acquirer obtains control of the acquiree, in CCYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=116868678&loc=d3e848-128460

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=116868678&loc=d3e845-128460

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessAcquisitionEffectiveDateOfAcquisition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- 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

Name:	us-gaap_BusinessAcquisitionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6613-128477

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6578-128477

+ Details

Name:	us-gaap_BusinessCombinationConsiderationTransferred1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of assets acquired at the acquisition date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121647850&loc=d3e4845-128472

+ Details

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

- Definition

Amount of liabilities assumed at the acquisition date.

+ References

+ Details

Name:	us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585

+ Details

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

- Definition

The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585

+ Details

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

- Definition

Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121559654&loc=SL6759159-111685

+ Details

Name:	us-gaap_VariableInterestEntityOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_BusinessAcquisitionAxis=brka_MLMICInsuranceCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=brka_BerkshireHathawayEnergyCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=brka_DominionEnergyIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PartnerTypeOfPartnersCapitalAccountAxis=us-gaap_GeneralPartnerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PartnerTypeOfPartnersCapitalAccountAxis=us-gaap_LimitedPartnerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=brka_FirstAcquisitionAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=brka_SecondAcquisitionAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Business acquisitions - Narrative (Detail) $ in Millions				6 Months Ended	12 Months Ended
Business acquisitions - Narrative (Detail) $ in Millions	Nov. 01, 2020 USD ($) Bcfe mi	Oct. 05, 2020	Oct. 01, 2018 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Business Acquisition [Line Items]
Aggregate consideration paid for acquisitions, net of cash acquired					$ 2,532	$ 1,683	$ 3,279
MLMIC Insurance Company [Member]
Business Acquisition [Line Items]
Acquisition price			$ 2,500
Assets			6,100
Investments			5,200
Liabilities			3,600
Unpaid losses and loss adjustment expenses			$ 3,200
Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition [Line Items]
Aggregate consideration paid for acquisitions, net of cash acquired					$ 130	$ 1,700	$ 1,000
Berkshire Hathaway Energy [Member] \| Dominion Energy, Inc. [Member]
Business Acquisition [Line Items]
Business acquisition, contingent acquisition description					to acquire substantially all of Dominion’s natural gas transmission and storage business.
Berkshire Hathaway Energy [Member] \| Dominion Energy, Inc. [Member] \| Cove Point [Member]
Business Acquisition [Line Items]
Variable interest entity, ownership percentage	25.00%
Berkshire Hathaway Energy [Member] \| Dominion Energy, Inc. [Member] \| Cove Point [Member] \| General Partner [Member]
Business Acquisition [Line Items]
Variable interest entity, ownership percentage	100.00%
Berkshire Hathaway Energy [Member] \| Dominion Energy, Inc. [Member] \| Cove Point [Member] \| Limited Partner [Member]
Business Acquisition [Line Items]
Variable interest entity, ownership percentage	25.00%
Berkshire Hathaway Energy [Member] \| Dominion Energy, Inc. [Member] \| First Acquisition Agreement [Member]
Business Acquisition [Line Items]
Business acquisition, date of acquisition		Oct. 05, 2020
Business acquisition, date of completed	Nov. 01, 2020
Payment for acquisition of business in cash after post-closing adjustments	$ 2,500
Berkshire Hathaway Energy [Member] \| Dominion Energy, Inc. [Member] \| First Acquisition Agreement [Member] \| Cove Point [Member]
Business Acquisition [Line Items]
Natural gas storage capacity acquired \| Bcfe	420
Berkshire Hathaway Energy [Member] \| Dominion Energy, Inc. [Member] \| First Acquisition Agreement [Member] \| Cove Point [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Business acquisition, length of pipelines acquired \| mi	5,400
Berkshire Hathaway Energy [Member] \| Dominion Energy, Inc. [Member] \| Second Acquisition Agreement [Member]
Business Acquisition [Line Items]
Business acquisition, date of acquisition		Oct. 05, 2020
Berkshire Hathaway Energy [Member] \| Dominion Energy, Inc. [Member] \| Second Acquisition Agreement [Member] \| Forecast [Member]
Business Acquisition [Line Items]
Payment for acquisition of business in cash				$ 1,300