Derivative Financial Instruments and Hedging Activities Offsetting Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Apr. 30, 2019	Apr. 30, 2018
Offsetting Assets and Liabilities [Line Items]
Gross Amount of Derivative Assets	$ 43	$ 10
Gross Amount of Derivative Liabilities Offset Against Derivative Assets in Balance Sheet	(3)	(9)
Net Amount of Derivative Assets Presented in Balance Sheet	40	1
Gross Amount of Derivative Liabilities Not Offset Against Derivative Assets in Balance Sheet	0	(1)
Net Amount of Derivative Assets	40	0
Gross Amount of Derivative Liabilities	(9)	(48)
Gross Amount of Derivative Assets Offset Against Derivative Liabilities in Balance Sheet	3	9
Net Amount of Derivative Liabilities Presented in Balance Sheet	(6)	(39)
Gross Amount of Derivative Assets Not Offset Against Derivative Liabilities in Balance Sheet	0	1
Net Amount of Derivative Liabilities	$ (6)	$ (38)