Derivative Financial Instruments Offsetting Derivative Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Jul. 31, 2014	Apr. 30, 2014
Offsetting Assets and Liabilities [Line Items]
Gross Amount of Derivative Assets	$ 13	$ 17
Gross Amount of Derivative Liabilities Offset Against Derivative Assets in Balance Sheet	(10)	(10)
Net Amount of Derivative Assets Presented in Balance Sheet	3	7
Gross Amount of Derivative Liabilities Not Offset Against Derivative Assets in Balance Sheet	0	(2)
Net Amount of Derivative Assets	3	5
Gross Amount of Derivative Liabilities	(15)	(17)
Gross Amount of Derivative Assets Offset Against Derivative Liabilities in Balance Sheet	10	10
Net Amount of Derivative Liabilities Presented in Balance Sheet	5	7
Gross Amount of Derivative Assets Not Offset Against Derivative Liabilities in Balance Sheet	0	2
Net Amount of Derivative Liabilities	$ 5	$ 5