Income Taxes (Narrative) (Details) £ in Millions, $ in Millions			3 Months Ended		6 Months Ended			12 Months Ended
	Jan. 19, 2018 GBP (£)	Dec. 20, 2017 GBP (£)	Apr. 30, 2018 USD ($)	Apr. 30, 2017	Apr. 30, 2018 GBP (£)	Apr. 30, 2018 USD ($)	Apr. 30, 2017	Oct. 31, 2018	Oct. 31, 2017 USD ($)
Operating Loss Carryforwards [Line Items]
Repatriation tax						$ 177.9
Provisional tax expense						13.2
Current state and local tax expense (benefit)						8.1
Withholding taxes relating to the unremitted foreign earnings			$ 2.8			$ 2.8
Effective income tax rate			12.90%	4.20%	147.80%	147.80%	4.70%
Effective tax rate increase						$ 202.0
Unrecognized tax benefits			$ 63.6			63.6			$ 59.9
Unrecognized tax benefits that could be settled			$ 6.1			$ 6.1
UNITED KINGDOM
Operating Loss Carryforwards [Line Items]
Diverted profit tax | £		£ 31.0			£ 31.0
Payment for DPT | £	£ 31.0
Scenario, Forecast
Operating Loss Carryforwards [Line Items]
Blended tax rate								23.34%