Common stock - Narrative (Detail) (USD $)	12 Months Ended						1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Class B [Member] Vote	Dec. 31, 2012 Class A [Member] Vote	Dec. 31, 2011 Class A [Member]	Dec. 31, 2012 Preferred Stock [Member]	Dec. 31, 2012 Common Stock [Member]	Dec. 31, 2012 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				1,642,945	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, Berkshire's Board of Directors ("Berkshire's Board") approved a common stock repurchase program under which Berkshire may repurchase its Class A and Class B shares at prices no higher than a 10% premium over the book value of the shares. In December 2012, Berkshire's Board amended the repurchase program by raising the price limit to no higher than a 20% premium over book value.
Minimum cash equivalent threshold after repurchase of common stock shares, amount								$ 20,000,000,000
Payment for repurchase of common shares	$ 1,296,000,000	$ 67,000,000					$ 1,300,000,000