Earnings Per Share (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended
	Jul. 31, 2013	Jul. 31, 2012
Basic and diluted earnings per share
Net income	$ 143	$ 147
Net income available to common stockholders	$ 143	$ 147
Share data (in thousands):
Basic average common shares outstanding	213,709	213,168
Dilutive effect of stock-based awards	1,611	1,630
Diluted average common shares outstanding	215,320	214,798
Basic earnings per share	$ 0.67	$ 0.69
Diluted earnings per share	$ 0.66	$ 0.69