Common stock - Narrative (Detail)
 12 Months Ended
Dec. 31, 2018
USD ($)
Vote
shares
Dec. 31, 2017
shares
Dec. 31, 2016
shares
Dec. 31, 2015
shares
Class of Stock [Line Items]        
Preferred Stock, shares authorized 1,000,000      
Preferred Stock, shares issued 0      
Class A [Member]        
Class of Stock [Line Items]        
Number of votes entitled per share, number | Vote 1      
Shares outstanding 729,316 751,075 776,378 808,422
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 1,367,420,074 1,340,656,987 1,301,914,165 1,252,456,836
Equivalent Class A [Member]        
Class of Stock [Line Items]        
Shares outstanding 1,640,929 1,644,846    
Common Stock Repurchase Program [Member]        
Class of Stock [Line Items]        
Shares repurchase, authorization description For several years, Berkshire had a common stock repurchase program, which 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