Segment and Geographic Information - Financial Information by Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Oct. 31, 2020	Jul. 31, 2020	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2018
Revenues
Revenues	$ 1,484.6	$ 1,394.1	$ 1,496.0	$ 1,612.9	$ 1,648.0	$ 1,647.9	$ 1,594.7	$ 1,607.9	$ 5,987.6	$ 6,498.6	$ 6,442.2
Operating profit (loss)
Operating profit (loss)									95.7	208.3	138.6
Income from unconsolidated affiliates									2.2	3.0	3.2
Interest expense									(44.6)	(51.1)	(54.1)
Income from continuing operations before income taxes									53.3	160.2	87.7
Depreciation and amortization
Depreciation and amortization									96.4	107.4	112.5
Goodwill, impairment loss									163.8
Impairment loss									172.8	0.0	26.5
Operating Segments
Revenues
Revenues									6,110.0	6,626.3
Corporate
Operating profit (loss)
Operating profit (loss)									(146.9)	(159.0)	(168.8)
Depreciation and amortization
Depreciation and amortization									13.5	13.9	12.4
Segment Reconciling Items
Operating profit (loss)
Adjustment for tax deductions for energy efficient government buildings, included in Technical Solutions									(2.1)	0.1	(2.8)
Income from unconsolidated affiliates									(2.2)	(3.0)	(3.2)
Business & Industry
Depreciation and amortization
Goodwill, impairment loss									0.0
Business & Industry | Operating Segments
Revenues
Revenues									3,157.8	3,251.4	3,268.4
Operating profit (loss)
Operating profit (loss)									253.7	182.3	157.9
Depreciation and amortization
Depreciation and amortization									18.9	21.3	23.6
Technology & Manufacturing
Depreciation and amortization
Goodwill, impairment loss									0.0
Technology & Manufacturing | Operating Segments
Revenues
Revenues									956.0	917.0	925.4
Operating profit (loss)
Operating profit (loss)									84.4	72.5	67.4
Depreciation and amortization
Depreciation and amortization									12.5	14.3	15.6
Education
Depreciation and amortization
Goodwill, impairment loss									99.3
Education | Operating Segments
Revenues
Revenues									808.8	847.4	856.7
Operating profit (loss)
Operating profit (loss)									(41.1)	39.0	44.1
Depreciation and amortization
Depreciation and amortization									33.8	37.3	37.5
Aviation
Depreciation and amortization
Goodwill, impairment loss									55.5
Impairment loss									61.1
Aviation | Operating Segments
Revenues
Revenues									680.9	1,017.3	1,038.7
Operating profit (loss)
Operating profit (loss)									(59.6)	21.1	23.2
Depreciation and amortization
Depreciation and amortization									10.6	11.9	13.1
Technical Solutions
Depreciation and amortization
Goodwill, impairment loss									9.0
Impairment loss									12.4
Technical Solutions | Operating Segments
Revenues
Revenues									506.6	593.2	500.1
Operating profit (loss)
Operating profit (loss)									9.5	55.4	21.8
Depreciation and amortization
Depreciation and amortization									7.2	8.6	10.2
Government Services | Operating Segments
Operating profit (loss)
Operating profit (loss)									(0.1)	(0.1)	(0.8)
Elimination of inter-segment revenues | Operating Segments
Revenues
Revenues									$ (122.4)	$ (127.7)	$ (147.1)