Accumulated other comprehensive income (loss) (Details) $ in Thousands	6 Months Ended
	Jul. 01, 2017 USD ($)
Accumulated Other Comprehensive Income Rollforward [Roll Forward]
Balance as of December 31, 2016	$ 5,783,487
Balance as of July 1, 2017	6,454,493
Foreign currency translation adjustments
Accumulated Other Comprehensive Income Rollforward [Roll Forward]
Balance as of December 31, 2016	(825,354)
Current period other comprehensive income (loss) before reclassifications	197,088
Balance as of July 1, 2017	(628,266)
Pensions
Accumulated Other Comprehensive Income Rollforward [Roll Forward]
Balance as of December 31, 2016	(7,673)
Current period other comprehensive income (loss) before reclassifications	(848)
Balance as of July 1, 2017	(8,521)
AOCI attributable to parent
Accumulated Other Comprehensive Income Rollforward [Roll Forward]
Balance as of December 31, 2016	(833,027)
Current period other comprehensive income (loss) before reclassifications	196,240
Balance as of July 1, 2017	$ (636,787)