Accounts receivable (Tables)

12 Months Ended

Dec. 31, 2011

Notes To Financial Statements [Abstract]

Accounts receivable

In millions	December 31,	2011		2010
Freight		$	630	$	585
Non-freight			206		211
Gross accounts receivable			836		796
Allowance for doubtful accounts			(16)		(21)
Net accounts receivable		$	820	$	775