Retroactive reinsurance contracts - Narrative (Detail) - USD ($) $ in Billions	Mar. 31, 2024	Dec. 31, 2023
Retroactive Reinsurance [Member]
Effects of Reinsurance [Line Items]
Unamortized deferred charges of retroactive reinsurance contracts	$ 9.3	$ 9.5

The remaining unamortized excess of the estimated ultimate liability for claims and claim costs over the premiums earned with respect to retroactive property/casualty reinsurance contracts.

No definition available.

Name:	brka_UnamortizedDeferredChargesOnReinsuranceAssumed
Namespace Prefix:	brka_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant