Pension and Other Postretirement Benefits Pension plans whose assets (obligations) exceed obligations (assets) (Details) - USD ($) $ in Millions	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Total, Plan Assets	$ 594	$ 626
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plans with assets in excess of accumulated benefit obligation, Plan Assets	0	53
Plans with accumulated benefit obligation in excess of assets, Plan Assets	594	573
Total, Plan Assets	594	626	$ 605
Plans with assets in excess of accumulated benefit obligation, Accumulated Benefit Obligation	0	50
Plans with accumulated benefit obligation in excess of assets, Accumulated Benefit Obligation	776	710
Total, Accumulated Benefit Obligation	776	760
Plans with assets in excess of accumulated benefit obligation, Projected Benefit Obligation	0	52
Plans with accumulated benefit obligation in excess of assets, Projected Benefit Obligation	898	835
Total, Projected Benefit Obligation	$ 898	$ 887	$ 785