Offsetting Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended
	Jul. 31, 2019	Apr. 30, 2019
Offsetting Assets and Liabilities [Line Items]
Gross Amount of Derivative Assets	$ 57	$ 43
Gross Amount of Derivative Liabilities Offset Against Derivative Assets in Balance Sheet	(2)	(3)
Net Amount of Derivative Assets Presented in Balance Sheet	55	40
Gross Amount of Derivative Liabilities Not Offset Against Derivative Assets in Balance Sheet	0	0
Net Amount of Derivative Assets	55	40
Gross Amount of Derivative Liabilities	(10)	(9)
Gross Amount of Derivative Assets Offset Against Derivative Liabilities in Balance Sheet	2	3
Net Amount of Derivative Liabilities Presented in Balance Sheet	8	6
Gross Amount of Derivative Assets Not Offset Against Derivative Liabilities in Balance Sheet	0	0
Net Amount of Derivative Liabilities	$ 8	$ 6
Document Period End Date	Jul. 31, 2019