Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	Apr. 30, 2019	Apr. 30, 2018
Deferred tax assets:
Postretirement and other benefits	$ 87	$ 89
Accrued liabilities and other	23	36
Inventories	34	48
Loss and credit carryforwards	55	51
Valuation allowance	(25)	(29)
Total deferred tax assets, net	174	195
Deferred tax liabilities:
Intangible assets	(218)	(199)
Property, plant, and equipment	(73)	(64)
Other	(12)	(1)
Total deferred tax liabilities	(303)	(264)
Net deferred tax liability	$ (129)	$ (69)