Employee Benefit Plans - Multiemployer Plans Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2017
Multiemployer Plans, Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Contributions by ABM	$ 66.6	$ 65.3	$ 63.1
Multiemployer Plans, Pension Plans \| Defined Contribution Plans
Defined Benefit Plan Disclosure [Line Items]
Contributions by ABM	9.0	10.6	5.4
Multiemployer Plans, Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Contributions by ABM	$ 269.8	$ 263.4	$ 247.9

Amount of contributions made to multiemployer plan by employer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450691-114947

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947

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