Properties - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 30, 2016	Dec. 25, 2015
Property, Plant and Equipment [Line Items]
Percentage of labor costs relating to the deconstruction of old track	20.00%
Percentage of labor costs relating to the installation of new track	80.00%
Percentage of assets depreciated under the group-life method	86.00%
Total fixed assets	$ 44,324,000,000	$ 43,227,000,000
Depreciation	1,315,000,000	1,301,000,000	$ 1,208,000,000
Abnormal gains and losses	14,000,000	110,000,000
Impairment expense	25,000,000	0	0
Ties
Property, Plant and Equipment [Line Items]
Total fixed assets	$ 5,665,000,000	$ 5,368,000,000
Estimated useful life	27 years	27 years
Total Equipment
Property, Plant and Equipment [Line Items]
Total fixed assets	$ 11,606,000,000	$ 11,604,000,000
Life studies, frequency period	3 years
Total Road
Property, Plant and Equipment [Line Items]
Total fixed assets	$ 30,091,000,000	28,824,000,000
Life studies, frequency period	6 years
Abnormal gain (loss) on operating property
Property, Plant and Equipment [Line Items]
Abnormal gains and losses	$ 0	$ 0	0
Gain (loss) on non-operating property
Property, Plant and Equipment [Line Items]
Abnormal gains and losses			$ 59,000,000