Nature of Operations and Significant Accounting Policies (Business) (Details) mi in Thousands, employees in Thousands, carloads in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 25, 2015 USD ($) employees terminals railroads state port_terminals mi	Sep. 25, 2015 USD ($)	Jun. 26, 2015 USD ($)	Mar. 27, 2015 USD ($)	Dec. 26, 2014 USD ($)	Sep. 26, 2014 USD ($)	Jun. 27, 2014 USD ($)	Mar. 28, 2014 USD ($)	Dec. 25, 2015 USD ($) employees terminals railroads state carloads port_terminals mi	Dec. 26, 2014 USD ($)	Dec. 27, 2013 USD ($)
Revenue from External Customer [Line Items]
Number of employees | employees	29								29
Number of union employees | employees									24
Number of rail route miles | mi	21								21
Rail network states number | state	23								23
Number of short-line and regional railroads served | railroads	240								240
Revenue | $	$ 2,781	$ 2,939	$ 3,064	$ 3,027	$ 3,192	$ 3,221	$ 3,244	$ 3,012	$ 11,811	$ 12,669	$ 12,026
Minimum [Member]
Revenue from External Customer [Line Items]
Number of ocean, river and lake ports serviced (more than) | port_terminals	70								70
Merchandise business [Member]
Revenue from External Customer [Line Items]
Number of carloads | carloads									2.9
Percentage of total revenue									62.00%
Percentage of total volume									42.00%
Coal business [Member]
Revenue from External Customer [Line Items]
Number of carloads | carloads									1.1
Percentage of total revenue									19.00%
Percentage of total volume									16.00%
Intermodal business [Member]
Revenue from External Customer [Line Items]
Percentage of total revenue									15.00%
Percentage of total volume									42.00%
Number of terminals (more than) | terminals	50								50
Other business [Member]
Revenue from External Customer [Line Items]
Percentage of total revenue									4.00%