Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Jul. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Jan. 31, 2018	Jul. 31, 2019	Jul. 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		$ 21.5
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)
Effective income tax rate (percent)	18.90%		6.60%		24.50%	(17.10%)
Income tax (provision) benefit	$ (8.5)		$ (2.4)		$ (25.8)	$ 12.7
Discrete tax benefit from expiring statute of limitations	(2.0)		(4.2)		(2.0)	(4.1)
Tax benefit from certain credits	$ (0.5)
Unrecognized tax benefits, interest on income tax expense					1.4
Decrease in tax credits, work opportunity tax credit					1.3	1.5
Income tax benefit related to vesting of share-based compensation awards			$ (1.6)		$ (1.1)	(3.1)
Tax deductions for energy efficient government buildings						$ (2.6)