Income Taxes - Reconciliation of Total Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jul. 31, 2016	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance		$ 57.2	$ 82.5	$ 85.5
Additions for tax positions related to the current year		0.0	0.0	2.1
Additions for tax positions related to prior years		16.4	0.0	0.1
Reductions for tax positions related to prior years		(0.1)	(3.2)	0.0
Reductions for lapse of statute of limitations	$ (19.0)	(19.7)	(21.9)	(5.2)
Settlements		(0.3)	(0.2)	0.0
Ending Balance		$ 53.4	$ 57.2	$ 82.5