Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Basic and diluted earnings per share
Net income available to common stockholders	$ 282	$ 249	$ 468	$ 449
Share data (in thousands):
Basic average common shares outstanding	477,680	480,436	477,522	480,647
Dilutive effect of stock-based awards	2,801	3,155	2,760	3,316
Diluted average common shares outstanding	480,481	483,591	480,282	483,963
Basic earnings per share (dollars per share)	$ 0.59	$ 0.52	$ 0.98	$ 0.93
Diluted earnings per share (dollars per share)	$ 0.59	$ 0.52	$ 0.97	$ 0.93