Derivative financial instruments - OCI Movement (Details) - Interest Rate Contract - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Movement recognized in OCI in relation to:
—Fair value loss on cash flow hedges	$ (10.6)	$ (14.6)	$ (26.5)	$ (27.9)
—Deferred premium reclassified from OCI to net income	1.9	0.7	3.6	0.8
Total movement	$ (8.7)	(14.4)	$ (22.9)	(27.6)
Previously Reported
Movement recognized in OCI in relation to:
—Deferred premium reclassified from OCI to net income		$ 0.2		$ 0.3