Supplemental equity information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 29, 2014	Jun. 30, 2013	Jun. 29, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial loss	$ 11,798	$ 16,275	$ 23,233	$ 32,135
Income before income taxes	331,912	166,341	454,001	288,204
Income tax effect	(106,000)	(39,600)	(158,500)	(45,000)
Amounts reclassified from accumulated other comprehensive income (loss)	6,888	9,970	13,990	19,666
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	6,888	9,970	13,990	19,666
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service credit	(1,215)	(384)	(1,700)	(806)
Amortization of actuarial loss	11,798	16,275	23,233	32,135
Income before income taxes	10,583	15,891	21,533	31,329
Income tax effect	$ (3,695)	$ (5,921)	$ (7,543)	$ (11,663)