Income Taxes - Narrative (Details) £ in Millions, $ in Millions					12 Months Ended
	Jan. 17, 2019 USD ($)	Jan. 19, 2018 GBP (£)	Jan. 19, 2018 USD ($)	Dec. 20, 2017 GBP (£)	Oct. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Oct. 31, 2017 USD ($)	Feb. 26, 2019 GBP (£)	Feb. 26, 2019 USD ($)
Operating Loss Carryforwards [Line Items]
Diverted profit tax refund								£ 22.1	$ 29.0
Payment for diverted profit tax		£ 31.0	$ 42.0
Effective tax rate					2.30%	57.90%	5.30%
Statutory federal income tax rate					21.00%	23.34%	35.00%
Valuation allowance					$ 41.5	$ 39.1
Unrecognized tax benefits					49.7	68.9	$ 59.9
Unrecognized tax benefits that would impact the effective tax rate					41.7	46.6	38.1
Accrued gross interest and penalties related to uncertain tax positions					3.9	$ 4.4	$ 3.6
Significant change in unrecognized tax benefits that is reasonably possible during the next twelve months					21.7
United Kingdom
Operating Loss Carryforwards [Line Items]
Diverted profit tax	$ 116.0			£ 31.0
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards					23.1
Federal net operating losses expiring between 2022 and 2037					18.6
Federal net operating losses not subject to expiration					4.5
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards					37.5
Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research credit					$ 1.7