Income Tax (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Income Tax Contingency [Line Items]
Provision for income taxes	$ 29.7	$ 35.2	$ 88.8	$ 69.8
(Loss) income before income taxes	96.4	$ 11.5	171.5	$ (75.7)
Unrecognized tax benefits	215.8		215.8
Unrecognized tax benefits that would impact effective tax rate	198.4		198.4
Valuation allowance of deferred tax assets
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	$ 17.4		$ 17.4