Derivative financial instruments - Gain Loss From Derivative Instruments Not Designated As Hedging Instruments (Details) - Not designated as hedging instrument - USD ($) $ in Millions	3 Months Ended
	Apr. 03, 2021	Mar. 28, 2020
Derivative Instruments, Gain (Loss)
Gain (loss) on derivative, recognized in the income statement	$ 1.8	$ 0.8
Currency forward contracts | —Severance expenses included in SG&A
Derivative Instruments, Gain (Loss)
Gain (loss) on derivative, recognized in the income statement	1.8	0.3
Currency swap | —Currency swaps recognized in other income
Derivative Instruments, Gain (Loss)
Gain (loss) on derivative, recognized in the income statement	$ 0.0	$ 0.5