Pension plans - Defined contribution pension plans - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Contribution Plan [Abstract]
Contributions to defined contribution plans	$ 1,001	$ 912	$ 739

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