Common stock - Narrative (Detail) (USD $) In Billions, except Share data, unless otherwise specified	1 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2011 Class B [Member] Vote	Sep. 30, 2011 Class A [Member] Vote	Dec. 31, 2010 Class A [Member]
Common Stock [Line Items]
Ratio of dividend and distribution rights per Class B share to earnings per Class A share		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			1,651,154	1,648,120
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