Common stock - Narrative (Detail) (USD $)	6 Months Ended				6 Months Ended
	Jun. 30, 2013 Class B [Member] Vote	Jun. 30, 2013 Class A [Member] Vote	Dec. 31, 2012 Class A [Member]	Jun. 30, 2013 Preferred Stock [Member]	Jun. 30, 2013 Common Stock [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	0.0001	1
Number of shares of Class B stock obtainable from converting one Class A share	1,500
Class A equivalent shares outstanding		1,643,743	1,642,945
Preferred Stock, shares authorized				1,000,000
Preferred Stock, shares issued				0
Preferred Stock, shares outstanding				0
Shares repurchase, authorization description					In 2011, Berkshire's Board of Directors ("Berkshire's Board") approved a common stock repurchase program. Under the program, as amended in December 2012, 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. Berkshire may repurchase shares in the open market or through privately negotiated transactions. Berkshire's Board authorization does not specify a maximum number of shares to be repurchased.
Minimum cash equivalent threshold after repurchase of common stock shares, amount					$ 20,000,000,000