Reconciliation of Benefit Obligations and Funded Status of Postretirement Benefit Plans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 30, 2012		Dec. 25, 2011		Dec. 26, 2010
Change in benefit obligations
Benefit obligations at end of year	$ 3,573,085
Change in plan assets
Fair value of plan assets at end of year	2,594,250	[1]	2,518,515	[1]
Benefit obligations at end of year	3,573,085
Accrued postretirement benefit cost:
Noncurrent	149,937		163,699
Other Postretirement Benefit Plans, Defined Benefit
Change in benefit obligations
Benefit obligations at beginning of year	184,131		191,282
Service cost	545		611		713
Interest cost	7,744		9,205		10,606
Plan participants' contributions	10,362		10,896
Actuarial gain (loss)	(5,877)		2,482
Gross benefits paid	(29,245)		(32,386)
Federal subsidy on benefits paid	1,932		2,041
Benefit obligations at end of year	169,592		184,131		191,282
Change in plan assets
Fair value of plan assets at beginning of year	0		0
Employer contributions	18,883		21,490
Plan participants' contributions	10,362		10,896
Gross benefits paid	(29,245)		(32,386)
Fair value of plan assets at end of year	0		0		0
Benefit obligations at end of year	169,592		184,131		191,282
Accrued postretirement benefit cost:
Current	19,655		20,432
Noncurrent	$ 149,937		$ 163,699

[1] The company uses a Dec. 31 measurement date for its retirement plans.