Common stock (Tables)

12 Months Ended

Dec. 31, 2020

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, 2020 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, 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		(20,542	)		—			(20,542	)		31,492,234		—			31,492,234
Treasury stock acquired		—			(1,217	)		(1,217	)		—		(4,729,147	)		(4,729,147	)
Balance December 31, 2018		742,213			(12,897	)		729,316			1,373,558,983		(6,138,909	)		1,367,420,074
Conversions of Class A common stock to    Class B common stock and exercises of    replacement stock options		(22,906	)		—			(22,906	)		34,624,869		—			34,624,869
Treasury stock acquired		—			(4,440	)		(4,440	)		—		(17,563,410	)		(17,563,410	)
Balance December 31, 2019		719,307			(17,337	)		701,970			1,408,183,852		(23,702,319	)		1,384,481,533
Conversions of Class A common stock to    Class B common stock and exercises of    replacement stock options		(40,784	)		—			(40,784	)		61,176,000		—			61,176,000
Treasury stock acquired		—			(17,255	)		(17,255	)		—		(95,614,062	)		(95,614,062	)
Balance December 31, 2020		678,523			(34,592	)		643,931			1,469,359,852		(119,316,381	)		1,350,043,471