Pension plans - Defined contribution pension plans - Narrative (Detail) - USD ($) $ in Billions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Plan [Abstract]
Contributions to defined contribution plans	$ 1.4	$ 1.2	$ 1.0

Amount of employer contributions to a defined contribution plan.

No definition available.

Name:	brka_DefinedContributionPlanEmployerContributionAmount
Namespace Prefix:	brka_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration