Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Net foreign currency exchange gain/loss	$ 1.3	$ (23.7)	$ 0.6	$ (22.7)
Notional amount of derivative financial instruments outstanding	$ 1,300.0	$ 1,200.0	$ 1,400.0	$ 1,000.0
Average maturities of derivatives, days	28 days	36 days	29 days	36 days