Income Taxes (Deferred Tax Liabilities Not Recognized) (Details) (USD $) In Millions, unless otherwise specified	Apr. 30, 2013	Apr. 30, 2012
Deferred Tax Liability Not Recognized [Line Items]
Undistributed earnings of foreign subsidiaries	$ 641	$ 542
Undistributed Earnings of Foreign Subsidiaries [Member]
Deferred Tax Liability Not Recognized [Line Items]
Amount of unrecognized deferred tax liability	$ 141	$ 121