Income Tax (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 35.2	$ 8.6	$ 69.8	$ 34.4
(Loss) income before income taxes	11.5	$ (111.2)	(75.7)	$ (359.0)
Unrecognized tax benefits	344.8		344.8
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	312.3		312.3
Valuation Allowance of Deferred Tax Assets
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	$ 32.5		$ 32.5