Fair value measurement - Schedule of assets and liabilities measured at fair value on a recurring basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Mar. 28, 2020	Dec. 28, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Equity investments	$ 1.0	$ 1.1
Derivative assets	2.9	5.4
Derivative liabilities	(71.2)	(60.9)
Quoted prices in active markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Equity investments	1.0	1.1
Derivative assets	0.0	0.0
Derivative liabilities	0.0	0.0
Significant observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Equity investments	0.0	0.0
Derivative assets	2.9	5.4
Derivative liabilities	$ (71.2)	$ (60.9)