Investment gains/losses - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Sales and redemptions of equity securities		$ 9,011	$ 7,815
Taxable gains on sales of equity securities	$ 629	$ 1,359

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