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Investments in equity securities (Detail) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Summary of Investment Holdings [Line Items]    
Cost basis of investments $ 58,836us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis $ 58,370us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
Unrealized gains on investments 57,718us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax 60,137us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Unrealized losses on investments (1,023)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax (1,037)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Fair value of investments 115,531us-gaap_AvailableForSaleSecuritiesEquitySecurities [1] 117,470us-gaap_AvailableForSaleSecuritiesEquitySecurities [2]
Banks, insurance and finance [Member]    
Summary of Investment Holdings [Line Items]    
Cost basis of investments 22,948us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ invest_InvestmentSectorAxis
= brka_BanksInsuranceAndFinanceMember		 22,495us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ invest_InvestmentSectorAxis
= brka_BanksInsuranceAndFinanceMember
Unrealized gains on investments 30,964us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ invest_InvestmentSectorAxis
= brka_BanksInsuranceAndFinanceMember		 33,170us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ invest_InvestmentSectorAxis
= brka_BanksInsuranceAndFinanceMember
Fair value of investments 53,912us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ invest_InvestmentSectorAxis
= brka_BanksInsuranceAndFinanceMember		 55,665us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ invest_InvestmentSectorAxis
= brka_BanksInsuranceAndFinanceMember
Consumer products [Member]    
Summary of Investment Holdings [Line Items]    
Cost basis of investments 6,862us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ invest_InvestmentSectorAxis
= brka_ConsumerProductsMember		 6,951us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ invest_InvestmentSectorAxis
= brka_ConsumerProductsMember
Unrealized gains on investments 17,478us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ invest_InvestmentSectorAxis
= brka_ConsumerProductsMember		 18,389us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ invest_InvestmentSectorAxis
= brka_ConsumerProductsMember
Unrealized losses on investments (1)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ invest_InvestmentSectorAxis
= brka_ConsumerProductsMember		 (1)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ invest_InvestmentSectorAxis
= brka_ConsumerProductsMember
Fair value of investments 24,339us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ invest_InvestmentSectorAxis
= brka_ConsumerProductsMember		 25,339us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ invest_InvestmentSectorAxis
= brka_ConsumerProductsMember
Commercial, industrial and other [Member]    
Summary of Investment Holdings [Line Items]    
Cost basis of investments 29,026us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ invest_InvestmentSectorAxis
= brka_CommercialIndustrialAndOtherMember		 28,924us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis
/ invest_InvestmentSectorAxis
= brka_CommercialIndustrialAndOtherMember
Unrealized gains on investments 9,276us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ invest_InvestmentSectorAxis
= brka_CommercialIndustrialAndOtherMember		 8,578us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ invest_InvestmentSectorAxis
= brka_CommercialIndustrialAndOtherMember
Unrealized losses on investments (1,022)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ invest_InvestmentSectorAxis
= brka_CommercialIndustrialAndOtherMember		 (1,036)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ invest_InvestmentSectorAxis
= brka_CommercialIndustrialAndOtherMember
Fair value of investments $ 37,280us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ invest_InvestmentSectorAxis
= brka_CommercialIndustrialAndOtherMember		 $ 36,466us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ invest_InvestmentSectorAxis
= brka_CommercialIndustrialAndOtherMember
[1] Approximately 58% of the aggregate fair value was concentrated in the equity securities of four companies (American Express Company - $11.8 billion; Wells Fargo & Company - $26.7 billion; International Business Machines Corporation - $12.8 billion; and The Coca-Cola Company - $16.2 billion).
[2] Approximately 59% of the aggregate fair value was concentrated in the equity securities of four companies (American Express Company - $14.1 billion; Wells Fargo & Company - $26.5 billion; International Business Machines Corporation - $12.3 billion; and The Coca-Cola Company - $16.9 billion).