Common stock - Narrative (Detail)	9 Months Ended
	Sep. 30, 2015 USD ($) Vote shares	Dec. 31, 2014 shares
Class of Stock [Line Items]
Preferred Stock, shares authorized	1,000,000
Preferred Stock, shares issued	0
Preferred Stock, shares outstanding	0
Common Stock Repurchase Program [Member]
Class of Stock [Line Items]
Shares repurchase, authorization description	Berkshire's Board of Directors ("Berkshire's Board") has approved a common stock repurchase program under which Berkshire may repurchase its Class A and Class B shares at prices no higher than a 20% premium over the book value of the shares.
Minimum cash and cash equivalent threshold after repurchase of common stock shares, amount | $	$ 20,000,000,000
Number of shares acquired	0
Class B [Member]
Class of Stock [Line Items]
Ratio of net earnings per equivalent common share and dividend and distribution rights of Class B shares to Class A shares	0.000667
Number of votes entitled per share, number | Vote	0.0001
Number of shares of Class B stock obtainable from converting one Class A share	1,500
Class A [Member]
Class of Stock [Line Items]
Number of votes entitled per share, number | Vote	1
Class A equivalent shares outstanding	1,643,355	1,642,909