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Employee Benefit Plans - Multiemployer Plans Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended
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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

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