Other Postretirement Benefits - Changes in the Benefit Obligation and Plan Assets and Other Amounts (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 25, 2011	Dec. 26, 2010	Dec. 27, 2009
Other Postretirement Benefits
Benefit obligation	$ 2,263,562	$ 2,077,368	$ 1,901,846
Employer contributions	167,809	193,289
Service cost	13,739	13,941
Interest cost	113,284	116,125
Plan participants’ contributions	34	32
Actuarial loss	165,807	157,092
Benefits paid	(106,637)	(110,262)
Fair value of plan assets	1,464,729	1,381,811	1,150,915
Current liabilities	18,784	16,436
Noncurrent liabilities	780,049	679,121
Net amount recognized	(798,833)	(695,557)
Actuarial loss	(1,003,344)	(776,432)
Prior service cost	(1,959)	(2,762)
Total amount recognized in accumulated other comprehensive loss	1,005,303	779,194
Other Postretirement Benefit Plans, Defined Benefit [Member]
Other Postretirement Benefits
Benefit obligation	113,803	142,417	164,811
Employer contributions	14,371	15,945
Service cost	1,143	1,076	1,551
Interest cost	6,890	9,340	10,355
Plan participants’ contributions	4,659	4,569
Actuarial loss	13,436	(16,865)
Plan amendments	(35,712)	0
Benefits paid	(20,247)	(21,438)
Medicare subsidies received	1,217	924
Fair value of plan assets	0	0	0
Current liabilities	(9,611)	(11,794)
Noncurrent liabilities	(104,192)	(130,623)
Net amount recognized	(113,803)	(142,417)
Actuarial loss	43,114	31,967
Prior service cost	(136,469)	(117,350)
Total amount recognized in accumulated other comprehensive loss	$ (93,355)	$ (85,383)