Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended		12 Months Ended
	Apr. 30, 2019	Oct. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Apr. 30, 2019	Apr. 30, 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)
Increase (decrease) in tax credits, work opportunity tax credit	$ (1.3)		$ (1.5)		$ (1.4)	$ (1.5)
Unrecognized tax benefits, interest on income tax expense	0.7				1.4
Income tax benefit related to vesting of share-based compensation awards	$ (0.3)				$ (0.8)	(1.5)
Tax deductions for energy efficient government buildings			$ (2.0)			(2.3)
Discrete tax benefit, provision income tax expense benefit						$ 21.7