Common stock - Narrative (Detail) (USD $)	6 Months Ended			6 Months Ended
	Jun. 30, 2012 Class B [Member] Vote	Jun. 30, 2012 Class A [Member] Vote	Dec. 31, 2011 Class A [Member]	Jun. 30, 2012 Common Stock [Member]	Jun. 30, 2012 Preferred 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		1,651,922	1,650,806
Preferred Stock, shares authorized					1,000,000
Preferred Stock, shares issued					0
Preferred Stock, shares outstanding					0
Shares repurchase, authorization description				In September 2011, our Board of Directors approved a common stock repurchase program whereby it authorized Berkshire Hathaway to repurchase its Class A and Class B shares of Berkshire at prices no higher than a 10% premium over the book value of the shares.
Minimum cash equivalent threshold after repurchase of common stock shares, amount				$ 20,000,000,000