Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Oct. 31, 2018
Income Tax Disclosure [Abstract]
U.S. statutory federal rate (percent)	21.00%		23.30%
Net discrete tax benefit from remeasurement of deferred taxes at new rate due to Tax Act		$ 28.7
One-time transition tax on deemed repatriation of indefinitely reinvested earnings	$ 7.0
Increase tax benefit from remeasurement of deferred taxes at new rate due to Tax Act			$ 29.6
Remeasurement of one-time transition tax on deemed repatriation of indefinitely reinvested earnings			$ (4.5)
Unrecognized tax benefits, interest on income tax expense	0.7
Income tax benefit related to vesting of share-based compensation awards	0.5	1.5
Income tax (provision) benefit	$ (4.7)	22.2
Discrete tax benefit, provision income tax expense benefit		$ 21.7