Pension and Other Postretirement Benefits (Details 7) (USD $) In Millions, unless otherwise specified	Apr. 30, 2012	Apr. 30, 2011
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	$ 49	$ 50
Plans with assets in excess of accumulated benefit obligation, Accumulated Benefit Obligation	45	41
Plans with assets in excess of accumulated benefit obligation, Projected Benefit Obligation	46	42
Plans with accumulated benefit obligation in excess of assets, Plan Assets	459	417
Plans with accumulated benefit obligation in excess of assets, Accumulated Benefit Obligation	598	505
Plans with accumulated benefit obligation in excess of assets, Projected Benefit Obligation	681	571
Total, Plan Assets	508	467
Total, Accumulated Benefit Obligation	643	546
Total, Projected Benefit Obligation	$ 727	$ 613