Income taxes (Details) € in Billions	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 28, 2019 USD ($)	Jun. 29, 2019 USD ($)	Mar. 30, 2019 USD ($)	Sep. 29, 2018 USD ($)	Jun. 29, 2019 USD ($)	Sep. 28, 2019 USD ($)	Sep. 29, 2018 USD ($)	Sep. 28, 2019 EUR (€)
Operating Loss Carryforwards
Income tax expense (benefit)	$ 4,400,000			$ 7,200,000		$ (497,800,000)	$ 30,400,000
Pre-tax income	$ 41,900,000			$ 74,200,000		$ 171,500,000	$ 219,700,000
Effective income tax rate	10.50%			9.70%		(290.30%)	13.80%
Discrete tax expense (benefit)	$ 5,300,000	$ 25,100,000
Reduction in tax on ordinary operations	8,000,000
Foreign currency translation adjustment, tax						$ 26,500,000
Tax benefit related to reorganization		65,600,000
Change in valuation allowance			$ (617,300,000)		$ (605,100,000)
Non-operating cost						0	$ 21,100,000
Deferred tax asset, net	570,100,000		627,600,000			570,100,000
Deferred tax asset to be recognized in the next 12 months			10,300,000
Deferred tax asset, foreign	564,000,000	$ 615,600,000			$ 615,600,000	564,000,000
Indefinite lived net operating loss | €								€ 2.1
Net Operating Loss
Operating Loss Carryforwards
Change in valuation allowance			(6,200,000)			(3,400,000)
Foreign Tax Credits
Operating Loss Carryforwards
Deferred tax asset, net	$ 2,700,000		$ 4,300,000			$ 2,700,000