Derivative Financial Instruments Offsetting Derivative Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Oct. 31, 2013	Apr. 30, 2013
Offsetting Assets and Liabilities [Line Items]
Gross Amount of Derivative Assets	$ 7	$ 10
Gross Amount of Derivative Liabilities Offset Against Derivative Assets in Balance Sheet	(5)	(5)
Net Amount of Derivative Assets Presented in Balance Sheet	2	5
Gross Amount of Derivative Liabilities Not Offset Against Derivative Assets in Balance Sheet	(1)	(2)
Net Amount of Derivative Assets	1	3
Gross Amount of Derivative Liabilities	(15)	(9)
Gross Amount of Derivative Assets Offset Against Derivative Liabilities in Balance Sheet	5	5
Net Amount of Derivative Liabilities Presented in Balance Sheet	10	4
Gross Amount of Derivative Assets Not Offset Against Derivative Liabilities in Balance Sheet	1	2
Net Amount of Derivative Liabilities	$ 9	$ 2