Shareholders' equity - Change in accumulated other comprehensive income, net of tax (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jul. 02, 2017	Jun. 26, 2016	Jul. 02, 2017	Jun. 26, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			$ 2,137,517
Other comprehensive income (loss) before reclassifications			114,682	$ 9,976
Amounts reclassified from accumulated other comprehensive income	$ 2,231	$ 2,191	4,740	4,777
Net current-period other comprehensive income			119,422	14,753
Ending Balance	2,358,529		2,358,529
Cash Flow Hedges
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(2,424)	(2,491)
Other comprehensive income (loss) before reclassifications			2,684	(1,684)
Amounts reclassified from accumulated other comprehensive income			2,477	2,668
Net current-period other comprehensive income			5,161	984
Ending Balance	2,737	(1,507)	2,737	(1,507)
Pension and Other Postretirement Benefit Plans
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(136,596)	(138,887)
Other comprehensive income (loss) before reclassifications			(669)	375
Amounts reclassified from accumulated other comprehensive income	1,132	1,053	2,263	2,109
Net current-period other comprehensive income			1,594	2,484
Ending Balance	(135,002)	(136,403)	(135,002)	(136,403)
Foreign Currency Translation Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(299,697)	(229,746)
Other comprehensive income (loss) before reclassifications			112,667	11,285
Amounts reclassified from accumulated other comprehensive income			0	0
Net current-period other comprehensive income			112,667	11,285
Ending Balance	(187,030)	(218,461)	(187,030)	(218,461)
Accumulated Other Comprehensive (Loss) Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(438,717)	(371,124)
Ending Balance	$ (319,295)	$ (356,371)	$ (319,295)	$ (356,371)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount after tax, before reclassification adjustments of other comprehensive income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=66004921&loc=d3e1436-108581

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 45
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-URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669686-108580

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Amount of increase (decrease) in other comprehensive income, after tax, from changes classified as other.

+ References

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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-Publisher FASB
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- Definition

Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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