Employee Benefit Plans - Multiemployer Defined Benefit Pension Plans (Details) - USD ($) $ in Millions	12 Months Ended
Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2017
Multiemployer Plans [Line Items]
Entity Tax Identification Number	94-1369354
Multiemployer Plans, Pension Plans
Multiemployer Plans [Line Items]
Contributions by ABM	$ 66.6	$ 65.3	$ 63.1
Multiemployer Plans, Pension Plans \| Minimum
Multiemployer Plans [Line Items]
Green Zone funded percent - Minimum	80.00%	80.00%
Multiemployer Plans, Pension Plans \| Maximum
Multiemployer Plans [Line Items]
Red Zone funded percent - Maximum	65.00%	65.00%
Yellow Zone funded percent - Maximum	80.00%	80.00%
Multiemployer Plans, Pension Plans \| Building Service 32BJ Pension Fund
Multiemployer Plans [Line Items]
Entity Tax Identification Number	13-1879376
Multiemployer Plan Number	001
Pension Protection Act Zone Status	Red	Red
Pension Protection Act Zone Status, Date	Jun. 30, 2018	Jun. 30, 2017
FIP/RP Status Pending/Implemented	Implemented
Contributions by ABM	$ 19.3	$ 19.9	20.1
Surcharge Imposed	No
Expiration Dates of Collective Bargaining Agreements, Last	Dec. 31, 2019
Multiemployer Plans, Pension Plans \| Central Pension Fund of the IUOE & Participating Employers
Multiemployer Plans [Line Items]
Entity Tax Identification Number	36-6052390
Multiemployer Plan Number	001
Pension Protection Act Zone Status	Green	Green
Pension Protection Act Zone Status, Date	Jan. 31, 2019	Jan. 31, 2018
FIP/RP Status Pending/Implemented	NA
Contributions by ABM	$ 11.7	$ 11.0	10.7
Surcharge Imposed	NA
Expiration Dates of Collective Bargaining Agreements, First	Apr. 30, 2020
Expiration Dates of Collective Bargaining Agreements, Last	Dec. 31, 2022
Multiemployer Plans, Pension Plans \| S.E.I.U. National Industry Pension Fund
Multiemployer Plans [Line Items]
Entity Tax Identification Number	52-6148540
Multiemployer Plan Number	001
Pension Protection Act Zone Status	Red	Red
Pension Protection Act Zone Status, Date	Dec. 31, 2018	Dec. 31, 2017
FIP/RP Status Pending/Implemented	Implemented
Contributions by ABM	$ 10.6	$ 8.7	7.2
Surcharge Imposed	Yes
Expiration Dates of Collective Bargaining Agreements, First	Apr. 30, 2020
Expiration Dates of Collective Bargaining Agreements, Last	Jan. 31, 2023
Multiemployer Plans, Pension Plans \| SEIU Local 1 & Participating Employers Pension Trust
Multiemployer Plans [Line Items]
Entity Tax Identification Number	36-6486542
Multiemployer Plan Number	001
Pension Protection Act Zone Status	Green	Green
Pension Protection Act Zone Status, Date	Sep. 30, 2018	Sep. 30, 2017
FIP/RP Status Pending/Implemented	NA
Contributions by ABM	$ 5.1	$ 5.8	6.0
Surcharge Imposed	NA
Expiration Dates of Collective Bargaining Agreements, Last	Apr. 04, 2021
Multiemployer Plans, Pension Plans \| IUOE Stationary Engineers Local 39 Pension Plan
Multiemployer Plans [Line Items]
Entity Tax Identification Number	94-6118939
Multiemployer Plan Number	001
Pension Protection Act Zone Status	Green	Green
Pension Protection Act Zone Status, Date	Dec. 31, 2018	Dec. 31, 2017
FIP/RP Status Pending/Implemented	NA
Contributions by ABM	$ 4.6	$ 5.2	4.8
Surcharge Imposed	NA
Expiration Dates of Collective Bargaining Agreements, First	Nov. 30, 2020
Expiration Dates of Collective Bargaining Agreements, Last	Aug. 31, 2023
Multiemployer Plans, Pension Plans \| Local 68 Engineers Union Pension Plan
Multiemployer Plans [Line Items]
Entity Tax Identification Number	51-0176618
Multiemployer Plan Number	001
Pension Protection Act Zone Status	Yellow	Red
Pension Protection Act Zone Status, Date	Jun. 30, 2018	Jun. 30, 2017
FIP/RP Status Pending/Implemented	Implemented
Contributions by ABM	$ 3.2	$ 3.0	2.8
Surcharge Imposed	No
Expiration Dates of Collective Bargaining Agreements, First	Apr. 30, 2020
Expiration Dates of Collective Bargaining Agreements, Last	Aug. 31, 2022
Multiemployer Plans, Pension Plans \| Western Conference of Teamsters Pension Plan
Multiemployer Plans [Line Items]
Entity Tax Identification Number	91-6145047
Multiemployer Plan Number	001
Pension Protection Act Zone Status	Green	Green
Pension Protection Act Zone Status, Date	Dec. 31, 2018	Dec. 31, 2017
FIP/RP Status Pending/Implemented	NA
Contributions by ABM	$ 3.1	$ 3.1	3.5
Surcharge Imposed	NA
Expiration Dates of Collective Bargaining Agreements, First	May 31, 2020
Expiration Dates of Collective Bargaining Agreements, Last	Dec. 31, 2022
Multiemployer Plans, Pension Plans \| All Other Plans
Multiemployer Plans [Line Items]
Contributions by ABM	$ 9.0	$ 8.5	$ 8.0

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Red Zone Multiemployer Plans Funded Percentage

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Yellow Zone Multiemployer Plans Funded Percentage

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The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation 12B
-Number 240
-Section 12
-Subsection b-2

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Amount of contributions made to multiemployer plan by employer.

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Three digit plan number for a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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Indicate the multiemployer plan's certified zone status as currently required by the Pension Protection Act of 2006 or a subsequent amendment thereof. The zone status categories are red (critical status), orange (seriously endangered), yellow (endangered), and green (none of the above). The acceptable values are "red", "orange", "yellow", "green", "other", and "NA". A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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Date of the multiemployer plan's year end to which the certified zone status relates, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan that will expire first in a group of associated collective bargaining arrangements, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan that will expire last in a group of associated collective bargaining arrangements, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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Indicate whether a funding improvement plan or rehabilitation plan has been implemented or is pending for a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "pending", "implemented", "other", and "NA".

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- 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.

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Indicate whether the employer paid a surcharge to the pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "yes", and "NA".

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