Pension and Other Postretirement Benefits Pension plans whose assets (obligations) exceed obligations (assets) (Details) - USD ($) $ in Millions	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Total, Plan Assets	$ 749	$ 754
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plans with assets in excess of accumulated benefit obligation, Plan Assets	625	754
Plans with accumulated benefit obligation in excess of assets, Plan Assets	124	0
Total, Plan Assets	749	754	$ 780
Plans with assets in excess of accumulated benefit obligation, Accumulated Benefit Obligation	613	668
Plans with accumulated benefit obligation in excess of assets, Accumulated Benefit Obligation	277	136
Total, Accumulated Benefit Obligation	890	804
Plans with assets in excess of accumulated benefit obligation, Projected Benefit Obligation	698	752
Plans with accumulated benefit obligation in excess of assets, Projected Benefit Obligation	307	156
Total, Projected Benefit Obligation	$ 1,005	$ 908	$ 903