Income Taxes - Components of Income Tax Provision (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Current:
Federal		$ 112.5	$ 227.9	$ 125.5
State		18.2	16.7	15.4
Foreign		47.7	49.0	43.5
Total current income tax expense (benefit)		178.4	293.6	184.4
Deferred:
Federal		(23.2)	94.1	36.7
State		(2.0)	1.1	7.1
Foreign		3.9	1.6	2.3
Total deferred income tax expense (benefit)		(21.3)	96.8	46.1
Income tax expense (benefit)	$ 146.2	$ 157.1	$ 390.4	$ 230.5