Accumulated other comprehensive income (loss) - Changes in Accumulated OCI by Component and Reclassifications Out of Accumulated OCI (Details) $ in Millions	6 Months Ended
	Jul. 31, 2021 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,190.3
Other comprehensive income (loss) (“OCI”) before reclassifications	7.1
Amounts reclassified from AOCI to net income	0.8
Net current period OCI	7.9
Ending Balance	1,555.5
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(290.5)
Ending Balance	(282.6)
Foreign currency translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(238.9)
Other comprehensive income (loss) (“OCI”) before reclassifications	7.4
Amounts reclassified from AOCI to net income	0.0
Net current period OCI	7.4
Ending Balance	(231.5)
Gains (losses) on available-for-sale securities, net
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	0.5
Other comprehensive income (loss) (“OCI”) before reclassifications	(0.1)
Amounts reclassified from AOCI to net income	0.0
Net current period OCI	(0.1)
Ending Balance	0.4
Gains (losses) on cash flow hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(0.9)
Other comprehensive income (loss) (“OCI”) before reclassifications	(0.2)
Amounts reclassified from AOCI to net income	0.4
Net current period OCI	0.2
Ending Balance	(0.7)
Pension Plan | Actuarial gains (losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(47.2)
Other comprehensive income (loss) (“OCI”) before reclassifications	0.0
Amounts reclassified from AOCI to net income	0.3
Net current period OCI	0.3
Ending Balance	(46.9)
Pension Plan | Prior service credits (costs)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(4.0)
Other comprehensive income (loss) (“OCI”) before reclassifications	0.0
Amounts reclassified from AOCI to net income	0.1
Net current period OCI	0.1
Ending Balance	$ (3.9)