Unpaid losses and loss adjustment expenses - Reconciliation of unpaid losses and allocated loss adjustment expenses to balance sheet liability (Detail) - Insurance Group [Member] $ in Millions	Dec. 31, 2022 USD ($)
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid losses and ALAE, net	$ 97,203
Reinsurance recoverable	4,669
Unallocated loss adjustment expenses	2,232
Other losses and loss adjustment expenses	3,368
Unpaid losses and loss adjustment expenses	107,472
GEICO [Member] | Physical Damage [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid losses and ALAE, net	884
Reinsurance recoverable	5
GEICO [Member] | Auto Liability [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid losses and ALAE, net	20,930
Reinsurance recoverable	867
Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid losses and ALAE, net	8,980
Reinsurance recoverable	28
Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid losses and ALAE, net	18,491
Reinsurance recoverable	1,543
Berkshire Hathaway Reinsurance Group [Member] | Property [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid losses and ALAE, net	16,552
Reinsurance recoverable	787
Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid losses and ALAE, net	31,366
Reinsurance recoverable	$ 1,439