Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2020	Jan. 31, 2019
Basic and diluted earnings per share
Net income available to common stockholders	$ 231	$ 227	$ 699	$ 676
Share data (in thousands):
Basic average common shares outstanding	477,898	477,301	477,643	479,522
Dilutive effect of stock-based awards	2,859	2,798	2,793	3,143
Diluted average common shares outstanding	480,757	480,099	480,436	482,665
Basic earnings per share (dollars per share)	$ 0.48	$ 0.47	$ 1.46	$ 1.41
Diluted earnings per share (dollars per share)	$ 0.48	$ 0.47	$ 1.45	$ 1.40