Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	Apr. 30, 2018	Apr. 30, 2017
Deferred tax assets:
Postretirement and other benefits	$ 89	$ 173
Accrued liabilities and other	36	17
Inventories	48	27
Loss carryforwards	51	44
Valuation allowance	(29)	(30)
Total deferred tax assets, net	195	231
Deferred tax liabilities:
Intangible assets	(199)	(262)
Property, plant, and equipment	(64)	(90)
Other	(1)	(15)
Total deferred tax liabilities	(264)	(367)
Net deferred tax liability	$ (69)	$ (136)