Financial Instruments (Effects of Derivative Instruments on Condensed Consolidated Statements of Operations) (Details) - Foreign currency contracts - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in accumulated other comprehensive loss on derivatives (effective portion)	$ 6.8	$ 2.9	$ 20.1	$ (8.5)
Amount and location of (loss) gain reclassified from accumulated other comprehensive loss into (loss) income (effective portion)	(4.7)	5.3	(9.0)	6.9
Designated as hedging instrument | Net revenue
Derivative Instruments, Gain (Loss) [Line Items]
Amount and location of (loss) gain reclassified from accumulated other comprehensive loss into (loss) income (effective portion)	(2.5)	2.4	(8.5)	7.2
Designated as hedging instrument | Operating expenses
Derivative Instruments, Gain (Loss) [Line Items]
Amount and location of (loss) gain reclassified from accumulated other comprehensive loss into (loss) income (effective portion)	(2.2)	2.9	(0.5)	(0.3)
Designated as hedging instrument | Interest and other expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Amount and location of gain (loss) recognized in (loss) income on derivatives (ineffective portion and amount excluded from effectiveness testing)	0.9	0.0	1.4	(0.1)
Derivatives not designated as hedging instruments | Interest and other expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Amount and location of gain (loss) recognized on derivatives in net (loss)	$ 4.7	$ 0.9	$ 10.7	$ (7.4)