Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Jul. 31, 2019	Jul. 31, 2018
Basic and diluted earnings per share
Net income available to common stockholders	$ 186	$ 200
Share data (in thousands):
Basic average common shares outstanding	477,369	480,964
Dilutive effect of stock-based awards	2,719	3,477
Diluted average common shares outstanding	480,088	484,441
Basic earnings per share (dollars per share)	$ 0.39	$ 0.42
Diluted earnings per share (dollars per share)	$ 0.39	$ 0.41