Supplemental equity information (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 29, 2013	Sep. 23, 2012	Sep. 29, 2013	Sep. 23, 2012
Accumulated Other Comprehensive Income [Line Items]
Balance at	$ (699,771)	$ (584,568)	$ (701,141)	$ (595,839)
Other comprehensive income before reclassifications	16,455	6,428	(1,841)	3,407
Amounts reclassified from accumulated other comprehensive income	9,834	6,334	29,500	20,626
Other comprehensive income	26,289	12,762	27,659	24,033
Balance at	(673,482)	(571,806)	(673,482)	(571,806)
Retirement Plans [Member]
Accumulated Other Comprehensive Income [Line Items]
Balance at	(1,085,020)	(983,292)	(1,119,263)	(995,853)
Other comprehensive income before reclassifications	(14,016)	(15,735)	561	(17,466)
Amounts reclassified from accumulated other comprehensive income	9,834	6,334	29,500	20,626
Other comprehensive income	(4,182)	(9,401)	30,061	3,160
Balance at	(1,089,202)	(992,693)	(1,089,202)	(992,693)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income [Line Items]
Balance at	385,249	398,724	418,122	400,014
Other comprehensive income before reclassifications	30,471	22,163	(2,402)	20,873
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income	30,471	22,163	(2,402)	20,873
Balance at	$ 415,720	$ 420,887	$ 415,720	$ 420,887