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Assumptions Used to Determine Postretirement Cost (Detail) (Other Postretirement Benefit Plans, Defined Benefit)
12 Months Ended
Dec. 25, 2011
Dec. 26, 2010
Dec. 27, 2009
Other Postretirement Benefit Plans, Defined Benefit
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Discount rate 5.30% 5.80% 6.15%
Health care cost trend on coverage 6.50% 6.50% 7.00%
Ultimate trend rate 5.00% 5.00% 5.00%
Year that ultimate trend rate is reached 2015 2014 2014