Derivative Financial Instruments and Hedging Activities Offsetting Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Jan. 31, 2019	Apr. 30, 2018
Offsetting Assets and Liabilities [Line Items]
Gross Amount of Derivative Assets	$ 31	$ 10
Gross Amount of Derivative Liabilities Offset Against Derivative Assets in Balance Sheet	(7)	(9)
Net Amount of Derivative Assets Presented in Balance Sheet	24	1
Gross Amount of Derivative Liabilities Not Offset Against Derivative Assets in Balance Sheet	(1)	(1)
Net Amount of Derivative Assets	23	0
Gross Amount of Derivative Liabilities	(10)	(48)
Gross Amount of Derivative Assets Offset Against Derivative Liabilities in Balance Sheet	7	9
Net Amount of Derivative Liabilities Presented in Balance Sheet	3	39
Gross Amount of Derivative Assets Not Offset Against Derivative Liabilities in Balance Sheet	1	1
Net Amount of Derivative Liabilities	$ 2	$ 38