Revenue - Consolidated Statements of Operations (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 1,647.9	$ 1,624.3	$ 4,850.6	$ 4,793.5
Operating expenses	1,454.1	1,446.7	4,314.2	4,281.8
Selling, general and administrative expenses	119.8	110.0	340.9	326.8
Income tax provision	8.5	2.4	25.8	(12.7)
Net income	$ 36.8	$ 33.6	$ 79.4	$ 88.1
Net income per common share — Basic (in usd per share)	$ 0.55	$ 0.51	$ 1.19	$ 1.33
Net income per common share — Diluted (in usd per share)	$ 0.55	$ 0.51	$ 1.19	$ 1.33
Under Historical Guidance
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 1,661.0		$ 4,887.1
Operating expenses	1,466.6		4,350.3
Selling, general and administrative expenses	121.9		347.5
Income tax provision	8.1		24.2
Net income	$ 35.6		$ 74.8
Net income per common share — Basic (in usd per share)	$ 0.53		$ 1.13
Net income per common share — Diluted (in usd per share)	$ 0.53		$ 1.12
Effect of Adoption | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ (13.1)		$ (36.5)
Operating expenses	(12.5)		(36.1)
Selling, general and administrative expenses	(2.2)		(6.6)
Income tax provision	0.4		1.6
Net income	$ 1.2		$ 4.6
Net income per common share — Basic (in usd per share)	$ 0.02		$ 0.07
Net income per common share — Diluted (in usd per share)	$ 0.02		$ 0.07