Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Earnings Per Share [Abstract]
Net income available to common stockholders	$ 717	$ 669	$ 1,067
Share data (in thousands):
Basic average common shares outstanding (shares)	480,319	484,635	507,441
Dilutive effect of stock-based awards (shares)	3,929	3,442	3,259
Diluted average common shares outstanding (shares)	484,248	488,077	510,700
Basic earnings per share (dollars per share)	$ 1.49	$ 1.38	$ 2.10
Diluted earnings per share (dollars per share)	$ 1.48	$ 1.37	$ 2.09
Antidilutive common stock-based awards excluded from calculation of diluted earnings per share (shares)	805	2,145	1,131