Pension and Other Postretirement Benefits Pension plans whose assets (obligations) exceed obligations (assets) (Details) - USD ($) $ in Millions	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Total, Plan Assets	$ 754	$ 780
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plans with assets in excess of accumulated benefit obligation, Plan Assets	754	780
Plans with accumulated benefit obligation in excess of assets, Plan Assets	0	0
Total, Plan Assets	754	780	$ 623
Plans with assets in excess of accumulated benefit obligation, Accumulated Benefit Obligation	668	669
Plans with accumulated benefit obligation in excess of assets, Accumulated Benefit Obligation	136	123
Total, Accumulated Benefit Obligation	804	792
Plans with assets in excess of accumulated benefit obligation, Projected Benefit Obligation	752	754
Plans with accumulated benefit obligation in excess of assets, Projected Benefit Obligation	156	149
Total, Projected Benefit Obligation	$ 908	$ 903	$ 893