Pension and Other Postretirement Benefits (Plans with ABO in Excess of Plan Assets) (Details) - USD ($) $ in Millions	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total, Plan Assets	$ 836	$ 749
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation	(155)	(277)
Defined Benefit Plan Pension Plans With Assets In Excess Of Accumulated Benefit Obligation Aggregate Accumulated Benefit Obligation	(748)	(613)
Defined Benefit Plan, Accumulated Benefit Obligation	(903)	(890)
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets	0	124
Defined Benefit Plan Pension Plans With Assets In Excess Of Accumulated Benefit Obligation Aggregate Fair Value Of Plan Assets	836	625
Total, Plan Assets	$ 836	$ 749	$ 754