Common stock (Detail)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Class A [Member]
Class of Stock [Line Items]
Outstanding, beginning of year (in shares)	947,460	1,055,281	1,059,001
Outstanding, end of year (in shares)	938,244	947,460	1,055,281
Treasury shares acquired	(98)
Treasury shares, end of year	(98)
Shares issued, beginning of year (in shares)	947,460	1,055,281	1,059,001
Conversions of Class A common stock to Class B common stock and exercises of replacement stock options issued in a business acquisition	(9,118)	(188,752)	(3,720)
Shares issued, end of year (in shares)	938,342	947,460	1,055,281
Class A [Member] | BNSF [Member]
Class of Stock [Line Items]
Shares issued in business acquisition		80,931
Class B [Member]
Class of Stock [Line Items]
Outstanding, beginning of year (in shares)	1,050,990,468	744,701,300	735,349,800
Outstanding, end of year (in shares)	1,068,843,376	1,050,990,468	744,701,300
Treasury shares acquired	(801,985)
Treasury shares, end of year	(801,985)
Shares issued, beginning of year (in shares)	1,050,990,468	744,701,300	735,349,800
Shares issued in business acquisition	3,253,472
Conversions of Class A common stock to Class B common stock and exercises of replacement stock options issued in a business acquisition	15,401,421	285,312,547	9,351,500
Shares issued, end of year (in shares)	1,069,645,361	1,050,990,468	744,701,300
Class B [Member] | BNSF [Member]
Class of Stock [Line Items]
Shares issued in business acquisition		20,976,621