Revenue - Consolidated Statements of Operations (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2019	Apr. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 1,594.7	$ 1,580.8	$ 3,202.6	$ 3,169.2
Operating expenses	1,414.2	1,405.8	2,860.2	2,835.1
Selling, general and administrative expenses	108.4	107.8	221.1	216.8
Income tax provision	12.6	7.1	17.3	(15.1)
Net income	$ 29.7	$ 26.6	$ 42.7	$ 54.4
Net income per common share — Basic (in usd per share)	$ 0.45	$ 0.40	$ 0.64	$ 0.83
Net income per common share — Diluted (in usd per share)	$ 0.45	$ 0.40	$ 0.64	$ 0.82
Under Historical Guidance
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 1,608.1		$ 3,226.0
Operating expenses	1,426.4		2,883.7
Selling, general and administrative expenses	112.0		225.6
Income tax provision	12.0		16.1
Net income	$ 28.0		$ 39.2
Net income per common share — Basic (in usd per share)	$ 0.42		$ 0.59
Net income per common share — Diluted (in usd per share)	$ 0.42		$ 0.59
Effect of Adoption | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ (13.4)		$ (23.4)
Operating expenses	(12.2)		(23.6)
Selling, general and administrative expenses	(3.5)		(4.5)
Income tax provision	0.6		1.2
Net income	$ 1.7		$ 3.4
Net income per common share — Basic (in usd per share)	$ 0.03		$ 0.05
Net income per common share — Diluted (in usd per share)	$ 0.03		$ 0.05