Employee Benefit Plans - Multiemployer Plans Additional Information (Details) - USD ($) $ in Millions		12 Months Ended
		Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2016
Multiemployer Plans, Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Contributions by ABM	[1]	$ 65.3	$ 63.1	$ 59.3
Multiemployer Plans, Pension Plans | Defined Contribution Plans
Defined Benefit Plan Disclosure [Line Items]
Contributions by ABM		10.6	5.4	6.6
Multiemployer Plans, Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Contributions by ABM		$ 263.4	$ 247.9	$ 224.5

[1] To determine individually significant plans, we evaluated several factors, including our total contributions to the plan, our significance to the plan in terms of participating employees and contributions, and the funded status of the plan.