Income Tax (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 26.3	$ 16.0	$ 59.1	$ 34.6
(Loss) income before income taxes	66.5	$ (23.4)	75.1	$ (87.2)
Unrecognized tax benefits	214.4		214.4
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	196.7		196.7
Valuation allowance of deferred tax assets
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	$ 17.7		$ 17.7