Income Taxes (Deferred Tax Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Apr. 30, 2013	Apr. 30, 2012
Deferred tax assets:
Postretirement and other benefits	$ 136	$ 127
Accrued liabilities and other	26	24
Inventories	8	12
Loss and credit carryforwards	39	35
Valuation allowance	(25)	(24)
Total deferred tax assets, net	184	174
Deferred tax liabilities:
Intangible assets	258	228
Property, plant, and equipment	(50)	(49)
Other	(20)	(14)
Total deferred tax liabilities	(328)	(291)
Net deferred tax liability	$ (144)	$ (117)