Investment gains/losses - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Sales and redemptions of equity securities	$ 2,063	$ 4,240
Taxable gains on sales of equity securities	$ 518	$ 727

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