Investment gains/losses - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Sales and redemptions of equity securities	$ 14,336	$ 18,783	$ 19,512
Taxable gains on sales of equity securities	$ 3,200	$ 3,300

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