Investment gains/losses - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Investments Debt And Equity Securities [Abstract]
Sales and redemptions of equity securities	$ 2,166	$ 2,063
Taxable gains on sales of equity securities	$ 1,211	$ 518

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