Basis of Presentation and Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2021	Apr. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 1,497.4	$ 1,496.0	$ 2,989.8	$ 3,109.0
Management Reimbursement Revenue
Segment Reporting Information [Line Items]
Revenues	56.1	82.4	113.1	182.0
Management Reimbursement Revenue | Business & Industry
Segment Reporting Information [Line Items]
Revenues	43.2	61.7	86.6	135.4
Management Reimbursement Revenue | Aviation
Segment Reporting Information [Line Items]
Revenues	$ 12.9	$ 20.7	$ 26.5	$ 46.6