Related Party Transactions (Consolidated Balance Sheets Components) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2014	Dec. 25, 2015	Dec. 26, 2014
Related Party Transaction [Line Items]
Payable to Affiliates		$ 0	$ 0
TTX Company [Member] | Accounts Payable [Member]
Related Party Transaction [Line Items]
Payable to Affiliates		40	35
Corporate Joint Venture [Member] | Accounts Payable [Member]
Related Party Transaction [Line Items]
Payable to Affiliates		65	54
Corporate Joint Venture [Member] | Long-term Debt [Member] | CSX Promissory Note Related Party October 2044 [Member]
Related Party Transaction [Line Items]
Promissory notes payable to Conrail subsidiary		$ 73	73
Related party note, interest rate		2.89%
Corporate Joint Venture [Member] | Long-term Debt [Member] | CSXT Promissory Note Related Party October 2044 [Member]
Related Party Transaction [Line Items]
Promissory notes payable to Conrail subsidiary		$ 151	$ 151
Related party note, interest rate	2.89%	2.89%