Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019
Discrete tax items [Line Items]
Effective tax rate (percent)	35.40%	22.30%	19.00%	20.00%
Income tax expense (benefit)	$ 17.5	$ 39.1	$ (7.7)	$ 65.4
Change In Estimated 2018 Foreign Derived Intangible Income
Discrete tax items [Line Items]
Income tax expense (benefit)				$ (7.5)
Effective income tax rate reconciliation, deduction (percent)				2.30%