Employee Benefit Plans - Multiemployer Plans Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Cost recognized	$ 18.2	$ 24.3	$ 21.6
Multiemployer Plans, Pension Plans \| Defined Contribution Plans
Defined Benefit Plan Disclosure [Line Items]
Cost recognized	15.5	9.0	10.6
Multiemployer Plans, Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Contributions by ABM	$ 264.8	$ 269.8	$ 263.4

Amount of contributions made by entity participating in defined benefit plan, defined as multiple-employer plan but accounted for as multiemployer plan.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 30
-Section 55
-Paragraph 64
-URI http://asc.fasb.org/extlink&oid=65881987&loc=d3e16414-114935

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 30
-Section 55
-Paragraph 63
-URI http://asc.fasb.org/extlink&oid=65881987&loc=d3e16378-114935

Name:	us-gaap_MultipleEmployerPlanAccountedForAsMultiemployerPlanContributionByParticipatingEntity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration