Income Tax (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Income Tax Contingency [Line Items]
Provision for income taxes	$ 23.9	$ 29.7	$ 78.7	$ 88.8
(Loss) income before income taxes	156.1	$ 96.4	375.6	$ 171.5
Unrecognized tax benefits	221.3		221.3
Unrecognized tax benefits that would impact effective tax rate	203.7		203.7
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	$ 17.7		$ 17.7