Derivative financial instruments - OCI Movement (Details) - Interest Rate Contract - USD ($) $ in Millions	12 Months Ended
	Jan. 02, 2021	Dec. 28, 2019	Dec. 29, 2018
Movement recognized in OCI in relation to:
—Fair value loss on cash flow hedges	$ (29.1)	$ (31.7)	$ (4.5)
—Amortization to net income of prior period fair value losses	9.1	0.0	0.0
—Deferred premium reclassified from OCI to net income	3.6	2.5	5.4
Total movement	$ (16.4)	$ (29.2)	$ 0.9