Nature of Operations and Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 27, 2014 states mi	Jun. 28, 2013	Jun. 27, 2014 states mi	Jun. 28, 2013	Dec. 27, 2013
Background
Total number of rail route miles	21,000		21,000
Rail network states number	23		23
Fiscal Year
Number of weeks in fiscal quarter	91 days	91 days
Number of weeks in fiscal quarter ytd			182 days	182 days
Number of weeks in fiscal year			364 days	364 days
Allowance for Doubtful Accounts
Allowance for doubtful accounts	$ 35		$ 35		$ 33