Debt and Credit Agreements (Long-term Debt Instruments) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 27, 2013		Dec. 28, 2012
Debt Instrument [Line Items]
Total Long-term Debt Maturities (including current portion)	$ 9,555		$ 9,832
Less Debt Due within One Year	(533)	[1]	(780)	[1]
Long-term Debt (excluding current portion)	9,022	[1]	9,052	[1]
Notes Payable [Member]
Debt Instrument [Line Items]
Average Interest Rates (in hundredths)	5.70%
Total Long-term Debt Maturities (including current portion)	8,935		9,151
Equipment Obligations [Member]
Debt Instrument [Line Items]
Average Interest Rates (in hundredths)	7.30%	[2]
Total Long-term Debt Maturities (including current portion)	602	[2]	667	[2]
Capital Leases [Member]
Debt Instrument [Line Items]
Average Interest Rates (in hundredths)	8.10%
Total Long-term Debt Maturities (including current portion)	16		12
Convertible Debt [Member]
Debt Instrument [Line Items]
Average Interest Rates (in hundredths)	1.00%
Total Long-term Debt Maturities (including current portion)	$ 2		$ 2

[1] See the revision of prior period financial statements in Note 1. Nature of Operations and Significant Accounting Policies.

[2] These obligations are secured by an interest in certain railroad equipment.