Common stock (Detail)	3 Months Ended
	Mar. 31, 2021 shares
Class A [Member]
Class of Stock [Line Items]
Shares issued, beginning balance	678,523
Treasury shares, beginning balance	(34,592)
Shares outstanding, beginning balance	643,931
Conversions of Class A to Class B common stock, Issued	(896)
Conversions of Class A to Class B common stock, Outstanding	(896)
Treasury stock acquired	(4,606)
Shares issued, ending balance	677,627
Treasury shares, ending balance	(39,198)
Shares outstanding, ending balance	638,429
Class B [Member]
Class of Stock [Line Items]
Shares issued, beginning balance	1,469,359,852
Treasury shares, beginning balance	(119,316,381)
Shares outstanding, beginning balance	1,350,043,471
Conversions of Class A to Class B common stock, Issued	1,344,000
Conversions of Class A to Class B common stock, Outstanding	1,344,000
Treasury stock acquired	(20,547,740)
Shares issued, ending balance	1,470,703,852
Treasury shares, ending balance	(139,864,121)
Shares outstanding, ending balance	1,330,839,731