Accounting Policies (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	12 Months Ended
	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2010
Basic and diluted earnings per share
Basic and diluted net income	$ 513	$ 572	$ 449
Income allocated to participating securities		(1)	(1)
Net income available to common stockholders	$ 513	$ 571	$ 448
Share data (in thousands):
Basic average common shares outstanding	143,019	145,603	147,834
Dilutive effect of stock-based awards	1,036	910	741
Diluted average common shares outstanding	144,055	146,513	148,575
Basic earnings per share	$ 3.59	$ 3.92	$ 3.03
Diluted earnings per share	$ 3.56	$ 3.90	$ 3.02