Common stock - Narrative (Detail)	9 Months Ended
	Sep. 30, 2019 USD ($) Vote shares	Dec. 31, 2018 shares
Class of Stock [Line Items]
Preferred Stock, shares authorized	1,000,000
Preferred Stock, shares issued	0
Common Stock Repurchase Program [Member]
Class of Stock [Line Items]
Shares repurchase, authorization description	For several years, Berkshire had a common stock repurchase program that permitted Berkshire to repurchase its Class A and Class B shares at prices no higher than a 20% premium over the book value of the shares. On July 17, 2018, Berkshire’s Board of Directors authorized an amendment to the program, permitting Berkshire to repurchase shares any time that Warren Buffett, Berkshire’s Chairman of the Board and Chief Executive Officer, and Charlie Munger, Vice Chairman of the Board, believe that the repurchase price is below Berkshire’s intrinsic value, conservatively determined.
Minimum cash, cash equivalents and U.S. Treasury Bills threshold after repurchase of common stock shares, amount | $	$ 20,000,000,000
Class A [Member]
Class of Stock [Line Items]
Number of votes entitled per share, number | Vote	1
Shares outstanding	708,983	729,316
Class B [Member]
Class of Stock [Line Items]
Number of votes entitled per share, number | Vote	0.0001
Economic equivalent of Class B share to Class A share	0.0667%
Number of shares of Class B stock obtainable from converting one Class A share	1,500
Shares outstanding	1,384,102,610	1,367,420,074
Equivalent Class A [Member]
Class of Stock [Line Items]
Shares outstanding	1,631,718	1,640,929