Nature of Operations and Significant Accounting Policies - Narrative (Details) mi in Thousands, $ in Millions	6 Months Ended
Jun. 26, 2015 USD ($) state mi	Jun. 27, 2014	Dec. 26, 2014 USD ($)
Background
Total number of rail route miles	21
Number of states rail network serves \| state	23
Fiscal Year
Number of days in fiscal year	364 days	364 days
Number of days in fiscal quarter	91 days	91 days
Number of days in fiscal quarter YTD	182 days	182 days
Allowance for Doubtful Accounts
Allowance for doubtful accounts \| $	$ 37		$ 41

A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.4)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5074-111524

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Period Type:	instant