Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Jul. 31, 2019	Jan. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018	Oct. 31, 2018
Income Tax Disclosure [Abstract]
Income tax benefit to finalize tax effects of 2017 Act		$ 4.4
Effective income tax rate expense (benefit)	5.40%		(11.50%)	0.90%	82.10%
Provisional charge related to 2017 Act recorded in fiscal 2018						$ 196.7
Discrete tax benefits				$ 26.7
Unrecognized tax benefits	$ 50.7			50.7		$ 68.9
Unrecognized tax benefits that could be settled during the next twelve months	$ 8.1			$ 8.1