Other Postretirement Benefits - Changes in the Benefit Obligations Recognized in Other Comprehensive Income (Details) (USD $)	1 Months Ended	12 Months Ended
	Jan. 31, 2012	Dec. 30, 2012	Dec. 25, 2011	Dec. 26, 2010
Other Postretirement Benefits
Additional postretirement costs		$ 18,000,000	$ 16,000,000	$ 18,000,000
Other Postretirement Benefit Plans, Defined Benefit [Member]
Other Postretirement Benefits
Net actuarial loss/(gain)		(11,562,000)	(13,436,000)	16,865,000
Prior service credit		0	(35,712,000)	0
Recognized actuarial loss		(3,328,000)	(2,289,000)	(3,129,000)
Amortization of prior service credit		15,112,000	16,593,000	15,602,000
Effect of curtailment	27,200,000	27,213,000	0	0
Total recognized in other comprehensive (income)/loss		50,559,000	(7,972,000)	(4,392,000)
Net periodic pension cost/(income)		(33,055,000)	(6,271,000)	(2,057,000)
Total recognized in net periodic benefit cost and other comprehensive loss		17,504,000	(14,243,000)	(6,449,000)
Estimated actuarial loss that will be amortized from accumulated other comprehensive loss into net periodic pension cost over the next fiscal year		4,000,000
Estimated prior service cost that will be amortized from accumulated other comprehensive loss into net periodic pension cost over the next fiscal year		$ 15,000,000