Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	Apr. 30, 2020	Apr. 30, 2019
Deferred tax assets:
Postretirement and other benefits	$ 110	$ 87
Accrued liabilities and other	23	23
Inventories	26	34
Lease liabilities	14	0
Loss and credit carryforwards	57	55
Valuation allowance	(22)	(25)
Total deferred tax assets, net	208	174
Deferred tax liabilities:
Intangible assets	(233)	(218)
Property, plant, and equipment	(90)	(73)
Right-of-use assets	(13)	0
Derivative instruments	(18)	(9)
Other	(16)	(3)
Total deferred tax liabilities	(370)	(303)
Net deferred tax liability	$ (162)	$ (129)