Pension and Other Postretirement Benefits Pension plans whose assets (obligations) exceed obligations (assets) (Details) - USD ($) $ in Millions	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Total, Plan Assets	$ 780	$ 623
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plans with assets in excess of accumulated benefit obligation, Plan Assets	780	48
Plans with accumulated benefit obligation in excess of assets, Plan Assets	0	575
Total, Plan Assets	780	623	$ 594
Plans with assets in excess of accumulated benefit obligation, Accumulated Benefit Obligation	669	47
Plans with accumulated benefit obligation in excess of assets, Accumulated Benefit Obligation	123	729
Total, Accumulated Benefit Obligation	792	776
Plans with assets in excess of accumulated benefit obligation, Projected Benefit Obligation	754	48
Plans with accumulated benefit obligation in excess of assets, Projected Benefit Obligation	149	845
Total, Projected Benefit Obligation	$ 903	$ 893	$ 898