Pension and Other Postretirement Benefits (Plans with PBO 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, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation	(941)	(1,005)
Defined Benefit Plan, Pension Plan with Plan Assets in Excess of Projected Benefit Obligation, Projected Benefit Obligation	(71)	0
Defined Benefit Plan, Benefit Obligation	(1,012)	(1,005)	$ (908)
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets	761	749
Defined Benefit Plan, Pension Plan with Plan Assets in Excess of Projected Benefit Obligation, Plan Assets	75	0
Total, Plan Assets	$ 836	$ 749	$ 754