Casualty, Environmental and Other Reserves (Loss Contingencies Roll Forward) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 26, 2014		Dec. 27, 2013	Dec. 28, 2012
Casualty Reserves [Member]
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	$ 280		$ 325	$ 372
Charged to Expense	89	[1]	54	51
Payments	(104)		(99)	(98)
Balance end of period	265		280	325
Environmental Reserves [Member]
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	100		88	83
Charged to Expense	57	[1]	48	35
Payments	(63)		(36)	(30)
Balance end of period	94		100	88
Other Reserves [Member]
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	71		64	64
Charged to Expense	30	[1]	38	36
Payments	(42)		(31)	(36)
Balance end of period	59		71	64
Casualty, Environmental and Other [Member]
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	451		477	519
Charged to Expense	176	[1]	140	122
Payments	(209)		(166)	(164)
Balance end of period	$ 418		$ 451	$ 477

[1] Increase in expense in 2014 is primarily due to the resolution of personal injury claims for prior years.