Pension and Other Postretirement Benefits (Funded Status of Pension Plan Assets) (Details) (USD $) In Millions, unless otherwise specified	Apr. 30, 2013	Apr. 30, 2012
Pension plans that have assets in excess of their accumulated benefit obligations with those whose assets are less than their obligations
Plans with assets in excess of accumulated benefit obligation, Plan Assets	$ 52	$ 49
Plans with accumulated benefit obligation in excess of assets, Plan Assets	521	459
Total, Plan Assets	573	508
Plans with assets in excess of accumulated benefit obligation, Accumulated Benefit Obligation	48	45
Plans with accumulated benefit obligation in excess of assets, Accumulated Benefit Obligation	647	598
Total, Accumulated Benefit Obligation	695	643
Plans with assets in excess of accumulated benefit obligation, Projected Benefit Obligation	50	46
Plans with accumulated benefit obligation in excess of assets, Projected Benefit Obligation	733	681
Total, Projected Benefit Obligation	$ 783	$ 727