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Employee Benefit Plans - Defined Contribution Plans (Details) $ in Millions | 12 Months Ended
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Oct. 31, 2020 USD ($) defined_contribution_plan | Oct. 31, 2019 USD ($) | Oct. 31, 2018 USD ($)
Retirement Benefits [Abstract] |  |  |
Number of defined contribution plans | defined_contribution_plan | 4 |  |
Cost recognized | $ | $ 18.2 | $ 24.3 | $ 21.6

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- Definition Number of Defined Contribution Plans + References No definition available. + Details
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Namespace Prefix: | abm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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Namespace Prefix: | us-gaap_
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