Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Basic and diluted earnings per share
Net income available to common stockholders	$ 227	$ 190	$ 676	$ 607
Share data (in thousands):
Basic average common shares outstanding	477,301	480,361	479,522	480,193
Dilutive effect of stock-based awards	2,798	3,883	3,143	3,318
Diluted average common shares outstanding	480,099	484,244	482,665	483,511
Basic earnings per share (dollars per share)	$ 0.47	$ 0.39	$ 1.41	$ 1.26
Diluted earnings per share (dollars per share)	$ 0.47	$ 0.39	$ 1.40	$ 1.25