Common stock (Detail)	6 Months Ended
	Jun. 30, 2020 shares
Class A [Member]
Class of Stock [Line Items]
Shares issued, beginning balance	719,307
Treasury shares, beginning balance	(17,337)
Shares outstanding, beginning balance	701,970
Conversions of Class A common stock to Class B common stock	(27,607)
Treasury stock acquired	(3,164)
Shares issued, ending balance	691,700
Treasury shares, ending balance	(20,501)
Shares outstanding, ending balance	671,199
Class B [Member]
Class of Stock [Line Items]
Shares issued, beginning balance	1,408,183,852
Treasury shares, beginning balance	(23,702,319)
Shares outstanding, beginning balance	1,384,481,533
Conversions of Class A common stock to Class B common stock	41,410,500
Treasury stock acquired	(31,731,259)
Shares issued, ending balance	1,449,594,352
Treasury shares, ending balance	(55,433,578)
Shares outstanding, ending balance	1,394,160,774