Common stock (Detail)	6 Months Ended
	Jun. 30, 2014
Class A [Member]
Class of Stock [Line Items]
Shares issued, beginning of year (in shares)	868,616
Conversions of Class A common stock to Class B common stock and exercises of replacement stock options issued in a business acquisition	(5,391)
Shares issued, end of period (in shares)	863,225
Treasury shares, beginning of year	(9,573)
Treasury shares acquired	(2,107)
Treasury shares, end of period	(11,680)
Outstanding, beginning of year (in shares)	859,043
Outstanding, end of period (in shares)	851,545
Class B [Member]
Class of Stock [Line Items]
Shares issued, beginning of year (in shares)	1,178,775,092
Conversions of Class A common stock to Class B common stock and exercises of replacement stock options issued in a business acquisition	8,819,007
Shares issued, end of period (in shares)	1,187,594,099
Treasury shares, beginning of year	(1,408,484)
Treasury shares acquired	(1,278)
Treasury shares, end of period	(1,409,762)
Outstanding, beginning of year (in shares)	1,177,366,608
Outstanding, end of period (in shares)	1,186,184,337