Significant business acquisitions - Narrative (Detail) $ in Millions			1 Months Ended	3 Months Ended			5 Months Ended	6 Months Ended
	Jan. 31, 2023 USD ($)	Oct. 19, 2022 USD ($)	Jan. 31, 2023 USD ($)	Jun. 30, 2023 USD ($) Store Location	Mar. 31, 2023 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) Store Location	Jun. 30, 2023 USD ($) Store Location	Jun. 30, 2022 USD ($)
Business Acquisition [Line Items]
Revenues				$ 65,383		$ 52,933		$ 125,128	$ 102,359
Net earnings attributable to Berkshire shareholders				35,912		(43,621)		71,416	(38,041)
Equity method earnings				$ 511		$ 204		$ 1,199	$ 543
Pilot Travel Centers LLC [Member]
Business Acquisition [Line Items]
Percentage of additional interest acquired	41.40%
Business acquisition, cash consideration	$ 8,200
Equity interest ownership percentage	38.60%		38.60%	38.60%			38.60%	38.60%
Revenues							$ 24,300
Net earnings attributable to Berkshire shareholders							$ 197
One-time, non-cash remeasurement gain recognized					$ 3,000
Equity method earnings			$ 105
Pilot Travel Centers LLC [Member] | Canadian Provinces [Member] | Travel Center Locations [Member]
Business Acquisition [Line Items]
Number of places retail locations located | Location				6			6	6
Pilot Travel Centers LLC [Member] | U.S. States [Member] | Travel Center Locations [Member]
Business Acquisition [Line Items]
Number of places retail locations located | Location				43			43	43
Pilot Travel Centers LLC [Member] | U.S. and Canada [Member] | Retail Site [Member] | Minimum [Member]
Business Acquisition [Line Items]
Number of retail | Store				150			150	150
Pilot Travel Centers LLC [Member] | U.S. and Canada [Member] | Travel Center Locations [Member] | Minimum [Member]
Business Acquisition [Line Items]
Number of retail | Store				650			650	650
Alleghany Corporation [Member]
Business Acquisition [Line Items]
Business acquisition, cash consideration		$ 11,500
Business acquisition, effective date of acquisition		Oct. 19, 2022