Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	Apr. 30, 2017	Apr. 30, 2016
Deferred tax assets:
Postretirement and other benefits	$ 173	$ 183
Accrued liabilities and other	17	10
Inventories	27	26
Loss and credit carryforwards	44	39
Valuation allowance	(30)	(25)
Total deferred tax assets, net	231	233
Deferred tax liabilities:
Intangible assets	(262)	(225)
Property, plant, and equipment	(90)	(83)
Other	(15)	(9)
Total deferred tax liabilities	(367)	(317)
Net deferred tax liability	$ (136)	$ (84)