Casualty, Environmental and Other Reserves (Casualty) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2010		Dec. 25, 2009		Dec. 30, 2011 claims	Jun. 01, 2010	May 31, 2010
Loss Contingencies [Line Items]
Change in Estimate	$ (49)	[1]	$ (127)	[1]
Casualty [Member]
Loss Contingencies [Line Items]
Self-insured retention amount per injury						50	25
Individual claims expected to exceed self-insured retention amount					0
Change in Estimate	(49)	[1]	(127)	[1]
Decrease in casualty reserves	30
Earnings per share after-tax effect from decrease in casualty reserves (in dollars per share)	$ 0.03
Personal Injury [Member]
Loss Contingencies [Line Items]
Change in Estimate	$ (24)	[1]

[1] Changes in estimates in 2010 and 2009 are the result of continued safety improvements and decreasing claim trends for both personal injury and occupational injuries. See below for more detailed discussion regarding these changes in estimates.