Income Tax (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019
Income Tax Contingency [Line Items]
Provision for income taxes	$ 30.8	$ 26.3	$ 54.8	$ 59.1
(Loss) income before income taxes	129.0	$ 66.5	219.5	$ 75.1
Unrecognized tax benefits	222.4		222.4
Unrecognized tax benefits that would impact effective tax rate	204.7		204.7
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