Business segment data - Revenues by segment (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Total revenues	$ 58,473	$ 64,370
BNSF [Member]
Segment Reporting Information [Line Items]
Total revenues	5,590
Berkshire Hathaway Energy [Member]
Segment Reporting Information [Line Items]
Total revenues	4,512
Manufacturing Businesses [Member]
Segment Reporting Information [Line Items]
Total revenues	12,912
McLane Company [Member]
Segment Reporting Information [Line Items]
Total revenues	12,189
Service and Retailing Businesses [Member]
Segment Reporting Information [Line Items]
Total revenues	6,560
Finance and Financial Products Reportable Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	2,060
Operating Businesses [Member]
Segment Reporting Information [Line Items]
Total revenues	58,495	64,441
Operating Businesses [Member] \| Insurance Group [Member]
Segment Reporting Information [Line Items]
Interest, dividend and other investment income	1,213	1,132
Total revenues	14,586	22,885
Operating Businesses [Member] \| Insurance Group [Member] \| GEICO [Member]
Segment Reporting Information [Line Items]
Premiums earned	7,915	6,845
Operating Businesses [Member] \| Insurance Group [Member] \| Berkshire Hathaway Reinsurance Group [Member]
Segment Reporting Information [Line Items]
Premiums earned	3,540	13,232
Operating Businesses [Member] \| Insurance Group [Member] \| Berkshire Hathaway Primary Group [Member]
Segment Reporting Information [Line Items]
Premiums earned	1,918	1,676
Operating Businesses [Member] \| BNSF [Member]
Segment Reporting Information [Line Items]
Total revenues	5,624	5,185
Operating Businesses [Member] \| Berkshire Hathaway Energy [Member]
Segment Reporting Information [Line Items]
Total revenues	4,512	4,231
Operating Businesses [Member] \| Manufacturing Businesses [Member]
Segment Reporting Information [Line Items]
Total revenues	12,934	12,097
Operating Businesses [Member] \| McLane Company [Member]
Segment Reporting Information [Line Items]
Total revenues	12,189	12,101
Operating Businesses [Member] \| Service and Retailing Businesses [Member]
Segment Reporting Information [Line Items]
Total revenues	6,587	6,093
Operating Businesses [Member] \| Finance and Financial Products Reportable Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	2,063	1,849
Corporate, Eliminations and Other [Member]
Segment Reporting Information [Line Items]
Total revenues	$ (22)	$ (71)

Amount including accretion (amortization) of purchase discount (premium) of interest income and dividend income on securities and investments.

No definition available.

+ Details

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

- Definition

Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.1)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(c))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 235
-Section S99
-Paragraph 2
-Subparagraph (SX 210.12-17)
-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574992-122915

+ Details

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

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=brka_BurlingtonNorthernSantaFeCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=brka_BerkshireHathawayEnergyCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=brka_ManufacturingBusinessesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=brka_McLaneCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=brka_ServiceAndRetailingBusinessesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=brka_FinanceAndFinancialProductsReportableSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=brka_BerkshireHathawayInsuranceGroupMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsegmentsAxis=brka_GeicoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsegmentsAxis=brka_BerkshireHathawayReinsuranceGroupMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsegmentsAxis=brka_BerkshireHathawayPrimaryGroupMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConsolidationItemsAxis=brka_CorporateReconcilingItemsAndEliminationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: