Common stock (Tables)

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Changes in issued, treasury and outstanding Berkshire common stock

Changes in Berkshire’s issued, treasury and outstanding common stock during the three years ending December 31, 2017 are shown in the table below.

	Class A, $5 Par Value (1,650,000 shares authorized)									Class B, $0.0033 Par Value (3,225,000,000 shares authorized)
	Issued			Treasury			Outstanding			Issued		Treasury			Outstanding
Balance December 31, 2014		838,019			(11,680	)		826,339			1,226,265,250		(1,409,762	)		1,224,855,488
Conversions of Class A common stock to Class B common stock and exercises of replacement stock options issued in a business acquisition		(17,917	)		—			(17,917	)		27,601,348		—			27,601,348
Balance December 31, 2015		820,102			(11,680	)		808,422			1,253,866,598		(1,409,762	)		1,252,456,836
Conversions of Class A common stock to Class B common stock and exercises of replacement stock options issued in a business acquisition		(32,044	)		—			(32,044	)		49,457,329		—			49,457,329
Balance December 31, 2016		788,058			(11,680	)		776,378			1,303,323,927		(1,409,762	)		1,301,914,165
Conversions of Class A common stock to Class B common stock and exercises of replacement stock options issued in a business acquisition		(25,303	)		—			(25,303	)		38,742,822		—			38,742,822
Balance December 31, 2017		762,755			(11,680	)		751,075			1,342,066,749		(1,409,762	)		1,340,656,987