Common stock - Narrative (Detail) (USD $)	1 Months Ended	3 Months Ended
	Dec. 31, 2012	Mar. 31, 2013 Vote
Class B [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
Number of shares of Class B stock obtainable from converting one Class A share		1,500
Shares repurchased	606,499
Class A [Member]
Class of Stock [Line Items]
Number of votes entitled per share, number		1
Class A equivalent shares outstanding	1,642,945	1,643,397
Shares repurchased	9,475
Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, shares authorized		1,000,000
Preferred Stock, shares issued		0
Preferred Stock, shares outstanding		0
Common Stock [Member]
Class of Stock [Line Items]
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
Payment for repurchase of common shares	1,300,000,000