Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Earnings Per Share [Abstract]
Net income available to common stockholders	$ 835	$ 717	$ 669
Share data (in thousands):
Basic average common shares outstanding (shares)	478,956	480,319	484,635
Dilutive effect of stock-based awards (shares)	3,111	3,929	3,442
Diluted average common shares outstanding (shares)	482,067	484,248	488,077
Basic earnings per share (dollars per share)	$ 1.74	$ 1.49	$ 1.38
Diluted earnings per share (dollars per share)	$ 1.73	$ 1.48	$ 1.37
Antidilutive common stock-based awards excluded from calculation of diluted earnings per share (shares)	447	805	2,145