Employee Benefit Plans - Multiemployer Defined Benefit Pension Plans (Details) - Multiemployer Plans, Pension Plans - USD ($) $ in Millions		12 Months Ended
		Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2016
Multiemployer Plans [Line Items]
Contributions by ABM	[1]	$ 65.3	$ 63.1	$ 59.3
Minimum
Multiemployer Plans [Line Items]
Green Zone funded percent - Minimum		80.00%	80.00%
Maximum
Multiemployer Plans [Line Items]
Red Zone funded percent - Maximum		65.00%	65.00%
Yellow Zone funded percent - Maximum		80.00%	80.00%
Building Service 32BJ Pension Fund
Multiemployer Plans [Line Items]
Entity Tax Identification Number	[1],[2]	131879376
Multiemployer Plan Number	[1],[2]	001
Pension Protection Act Zone Status	[1],[3]	Red	Red
Pension Protection Act Zone Status, Date	[1],[3]	Jun. 30, 2017	Jun. 30, 2016
FIP/RP Status Pending/Implemented	[1],[4]	Implemented
Contributions by ABM	[1]	$ 19.9	$ 20.1	17.0
Surcharge Imposed	[1],[5]	No
Expiration Dates of Collective Bargaining Agreements, Last	[1]	Dec. 31, 2019
Central Pension Fund of the IUOE & Participating Employers
Multiemployer Plans [Line Items]
Entity Tax Identification Number	[1],[2]	366052390
Multiemployer Plan Number	[1],[2]	001
Pension Protection Act Zone Status	[1],[3]	Green	Green
Pension Protection Act Zone Status, Date	[1],[3]	Jan. 31, 2018	Jan. 31, 2017
FIP/RP Status Pending/Implemented	[1],[5]	NA
Contributions by ABM	[1]	$ 11.0	$ 10.7	11.0
Surcharge Imposed	[1],[5]	NA
Expiration Dates of Collective Bargaining Agreements, First	[1]	Dec. 31, 2018
Expiration Dates of Collective Bargaining Agreements, Last	[1]	Dec. 31, 2021
S.E.I.U. National Industry Pension Fund
Multiemployer Plans [Line Items]
Entity Tax Identification Number	[1],[2]	526148540
Multiemployer Plan Number	[1],[2]	001
Pension Protection Act Zone Status	[1],[3]	Red	Red
Pension Protection Act Zone Status, Date	[1],[3]	Dec. 31, 2017	Dec. 31, 2016
FIP/RP Status Pending/Implemented	[1],[4]	Implemented
Contributions by ABM	[1]	$ 8.7	$ 7.2	6.8
Surcharge Imposed	[1],[5]	Yes
Expiration Dates of Collective Bargaining Agreements, First	[1]	Feb. 14, 2019
Expiration Dates of Collective Bargaining Agreements, Last	[1]	Jan. 31, 2023
Local 25 SEIU & Participating Employers Pension Trust
Multiemployer Plans [Line Items]
Entity Tax Identification Number	[1],[2]	366486542
Multiemployer Plan Number	[1],[2]	001
Pension Protection Act Zone Status	[1],[3]	Green	Green
Pension Protection Act Zone Status, Date	[1],[3]	Sep. 30, 2017	Sep. 30, 2016
FIP/RP Status Pending/Implemented	[1],[5]	NA
Contributions by ABM	[1]	$ 5.8	$ 6.0	6.2
Surcharge Imposed	[1],[5]	NA
Expiration Dates of Collective Bargaining Agreements, Last	[1]	Apr. 04, 2021
IUOE Stationary Engineers Local 39 Pension Plan
Multiemployer Plans [Line Items]
Entity Tax Identification Number	[1],[2]	946118939
Multiemployer Plan Number	[1],[2]	001
Pension Protection Act Zone Status	[1],[3]	Green	Green
Pension Protection Act Zone Status, Date	[1],[3]	Dec. 31, 2017	Dec. 31, 2016
FIP/RP Status Pending/Implemented	[1],[5]	NA
Contributions by ABM	[1]	$ 5.2	$ 4.8	5.2
Surcharge Imposed	[1],[5]	NA
Expiration Dates of Collective Bargaining Agreements, First	[1]	Feb. 28, 2019
Expiration Dates of Collective Bargaining Agreements, Last	[1]	Aug. 31, 2023
Western Conference of Teamsters Pension Plan
Multiemployer Plans [Line Items]
Entity Tax Identification Number	[1],[2]	916145047
Multiemployer Plan Number	[1],[2]	001
Pension Protection Act Zone Status	[1],[3]	Green	Green
Pension Protection Act Zone Status, Date	[1],[3]	Dec. 31, 2017	Dec. 31, 2016
FIP/RP Status Pending/Implemented	[1],[5]	NA
Contributions by ABM		$ 3.1	$ 3.5	0.9
Surcharge Imposed	[1],[5]	NA
Expiration Dates of Collective Bargaining Agreements, First	[1]	Nov. 30, 2018
Expiration Dates of Collective Bargaining Agreements, Last	[1]	Dec. 31, 2021
Local 68 Engineers Union Pension Plan
Multiemployer Plans [Line Items]
Entity Tax Identification Number	[1],[2]	510176618
Multiemployer Plan Number	[1],[2]	001
Pension Protection Act Zone Status	[1],[3]	Red	Green
Pension Protection Act Zone Status, Date	[1],[3]	Jun. 30, 2017	Jun. 30, 2016
FIP/RP Status Pending/Implemented	[1],[4]	Implemented
Contributions by ABM	[1]	$ 3.0	$ 2.8	2.8
Surcharge Imposed	[1],[5]	No
Expiration Dates of Collective Bargaining Agreements, First	[1]	Apr. 30, 2019
Expiration Dates of Collective Bargaining Agreements, Last	[1]	Sep. 30, 2021
All Other Plans
Multiemployer Plans [Line Items]
Contributions by ABM	[1]	$ 8.5	$ 8.0	$ 9.4

[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.

[2] The “EIN/PN” column provides the Employer Identification Number and the three-digit plan number assigned to the plan by the Internal Revenue Service (“IRS”).

[3] The Pension Protection Act Zone Status columns provide the two most recently available Pension Protection Act zone statuses from each plan. The zone status is based on information provided to us and other participating employers and is certified by each plan’s actuary. Among other factors, plans in the red zone are generally less than 65% funded, plans in the yellow zone are less than 80% funded, and plans in the green zone are at least 80% funded.

[4] Indicates whether a Financial Improvement Plan (“FIP”) for yellow zone plans or a Rehabilitation Plan (“RP”) for red zone plans is pending or implemented.

[5] Indicates whether our contribution in 2018 included an amount in addition to the contribution rate specified in the applicable collective bargaining agreement as imposed by a plan in the red zone.