Common stock (Tables)

3 Months Ended

Mar. 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 months ending March 31, 2018 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 at 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		(3,038	)		—			(3,038	)		4,806,083		—			4,806,083
Balance at March 31, 2018		759,717			(11,680	)		748,037			1,346,872,832		(1,409,762	)		1,345,463,070