Deferred Compensation And Retirement Plans (Reconciliation Of Benefit Obligation) (Parenthetical) (Detail) - CSV of COLI Contracts - USD ($) $ in Millions	Apr. 30, 2018	Apr. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Gross CSV	$ 186.8	$ 180.3
Outstanding policy loans	66.7	67.2
Deferred Compensation Plan
Defined Benefit Plan Disclosure [Line Items]
Gross CSV	186.8	180.3
Outstanding policy loans	$ 66.7	$ 67.2