Common stock - Narrative (Detail) (USD $) In Billions, except Share data, unless otherwise specified			12 Months Ended		1 Months Ended
	Dec. 31, 2011 Class A [Member] Vote	Dec. 31, 2010 Class A [Member]	Dec. 31, 2011 Class B [Member] Vote	Dec. 31, 2011 Preferred Stock [Member]	Sep. 30, 2011 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	1		0.0001
Number of shares of Class B stock obtainable from converting one Class A share			1,500
Class A equivalent shares outstanding	1,650,806	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