Income Taxes - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Jan. 31, 2018 USD ($)	Oct. 31, 2018 USD ($) state	Oct. 31, 2017 USD ($)	Oct. 31, 2016 USD ($)
Income Taxes [Line Items]
U.S. statutory rate		23.30%	35.00%	35.00%
Net discrete tax benefit from remeasurement of deferred taxes at new rate due to Tax Act		$ 29.6
One-time transition tax		4.5
Tax benefits, implementation of tax act	$ 22.6	23.2
Tax benefits, adjustments		1.9
Tax benefit related to lapse of statute of limitations		5.8	$ 17.8
Interest on tax benefits related to lapse of statute of limitations		1.0
Tax benefit related to share-based compensation		3.4	3.6
Income tax benefit related to deduction for energy efficient government buildings		2.8	1.9
Work opportunity tax credit, adjustment		1.0
Interest on income taxes			1.2
Tax credits		24.6
Unrecognized tax benefits that would impact effective tax rate		35.8	50.5	$ 52.0
Maximum decrease in unrecognized tax benefits that is reasonably possible		5.6
Uncertain tax positions, interest and penalties accrued		1.0	1.9
Unrecognized tax benefits, interest and penalties benefit		$ (1.0)	$ (0.5)	$ (0.9)
Number of states in which entity operates | state		50
State and Local Jurisdiction
Income Taxes [Line Items]
Operating loss carryforwards		$ 255.0
Federal
Income Taxes [Line Items]
Operating loss carryforwards		$ 25.7