Investment gains/losses - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Sales and redemptions of equity securities		$ 14,164	$ 10,572
Taxable gains on sales of equity securities	$ 1,329	$ 2,688

The taxable gains on sales of equity securities represent the difference between the proceeds from sales and the original cost.

No definition available.

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