Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Oct. 31, 2018
Income Tax Disclosure [Abstract]
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
Income tax benefit (provision)	22.2	$ (5.9)
Discrete tax benefit related to enactment of Tax Act	$ 21.7
Income tax benefit related to vesting of share-based compensation awards		$ 2.0
Forecast
Income Taxes [Line Items]
U.S. statutory federal rate (percent)			23.30%