Common stock (Detail)	3 Months Ended
	Mar. 31, 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	(4,290)
Treasury stock acquired	(1,342)
Shares issued, ending balance	715,017
Treasury shares, ending balance	(18,679)
Shares outstanding, ending balance	696,338
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	6,435,000
Treasury stock acquired	(5,388,663)
Shares issued, ending balance	1,414,618,852
Treasury shares, ending balance	(29,090,982)
Shares outstanding, ending balance	1,385,527,870