Income Taxes - Components of Income Tax Provision (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Current:
Federal	$ 79.7	$ 112.5	$ 227.9
State	11.7	18.2	16.7
Foreign	51.2	47.7	49.0
Total current income tax expense (benefit)	142.6	178.4	293.6
Deferred:
Federal	10.9	(23.2)	94.1
State	0.6	(2.0)	1.1
Foreign	(4.9)	3.9	1.6
Total deferred income tax expense (benefit)	6.6	(21.3)	96.8
Income tax expense (benefit)	$ 149.2	$ 157.1	$ 390.4