Pension and Other Postretirement Benefits Pension plans whose assets (obligations) exceed obligations (assets) (Details) - USD ($) $ in Millions	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Total, Plan Assets	$ 623	$ 594
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plans with assets in excess of accumulated benefit obligation, Plan Assets	48	0
Plans with accumulated benefit obligation in excess of assets, Plan Assets	575	594
Total, Plan Assets	623	594	$ 626
Plans with assets in excess of accumulated benefit obligation, Accumulated Benefit Obligation	47	0
Plans with accumulated benefit obligation in excess of assets, Accumulated Benefit Obligation	729	776
Total, Accumulated Benefit Obligation	776	776
Plans with assets in excess of accumulated benefit obligation, Projected Benefit Obligation	48	0
Plans with accumulated benefit obligation in excess of assets, Projected Benefit Obligation	845	898
Total, Projected Benefit Obligation	$ 893	$ 898	$ 887