Investments in fixed maturity securities - Narrative (Detail) - Foreign governments [Member]	Sep. 30, 2016
AA or Higher Credit Rating [Member]
Summary of Investment Holdings [Line Items]
Percentage of fixed maturity investments by credit rating	92.00%
United Kingdom, Germany, Australia or Canada [Member]
Summary of Investment Holdings [Line Items]
Percentage of fixed maturity investments by geographic location	80.00%

The percentage of the available-for-sale debt securities portfolio as of the reporting date that originate from or are guaranteed by a specified country or countries.

No definition available.

Name:	brka_PercentageOfAvailableForSaleSecuritiesDebtSecuritiesByGeographicLocation
Namespace Prefix:	brka_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant