Insurance - Insurance Related Balances and Activity (Details) - USD ($) $ in Millions	Jul. 31, 2018	Oct. 31, 2017
Liability for Claims and Claims Adjustment Expense [Line Items]
Insurance recoverables	$ 73.8	$ 73.1
Claim Types Excluding Medical and Dental
Liability for Claims and Claims Adjustment Expense [Line Items]
Insurance claim reserves	500.4	485.6
Medical and Dental Claims
Liability for Claims and Claims Adjustment Expense [Line Items]
Insurance claim reserves	$ 8.9	$ 9.8

Carrying amount as of the balance sheet date of amounts expected to be recovered under the terms of insurance contracts.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_EstimatedInsuranceRecoveries
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpenseLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount (including both current and noncurrent portions) of accrued known and estimated losses incurred as of the balance sheet date for which no insurance coverage exists, and for which a claim has been made or is probable of being asserted, typically arising from workmen's compensation-type of incidents and personal injury to nonemployees from accidents on the entity's property.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.24)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_SelfInsuranceReserve
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	abm_InsurancePoliciesAxis=abm_AllOtherClaimTypesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	abm_InsurancePoliciesAxis=abm_MedicalAndDentalSelfInsuranceProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: