Derivative Instruments (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2019 USD ($)	Jul. 31, 2018 USD ($)	Jul. 31, 2019 USD ($)	Jul. 31, 2018 USD ($)
Derivative [Line Items]
Weighted Average Notional Amount Of Foreign Currency Derivatives	$ 1,200.0	$ 1,300.0	$ 1,200.0	$ 1,400.0
Derivative, Average Remaining Maturity	26 days	28 days	25 days	29 days
Net Investment Hedging [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held		0		0
Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held		0		0
Derivative, Notional Amount	$ 4.5		$ 4.5