Common stock (Tables)

12 Months Ended

Dec. 31, 2018

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, 2018 are shown in the table below. In addition to our common stock, 1,000,000 shares of preferred stock are authorized, but none are issued.

	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, 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
Conversions of Class A common stock to Class B common stock and exercises of replacement stock options issued in a business acquisition		(20,542	)		—			(20,542	)		31,492,234		—			31,492,234
Treasury stock acquired		—			(1,217	)		(1,217	)		—		(4,729,147	)		(4,729,147	)
Balance at December 31, 2018		742,213			(12,897	)		729,316			1,373,558,983		(6,138,909	)		1,367,420,074