Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Basic and diluted earnings per share
Net income available to common stockholders	$ 249	$ 239	$ 449	$ 417
Share data (in thousands):
Basic average common shares outstanding	480,436	480,150	480,647	480,095
Dilutive effect of stock-based awards	3,155	3,134	3,316	3,035
Diluted average common shares outstanding	483,591	483,284	483,963	483,130
Basic earnings per share (dollars per share)	$ 0.52	$ 0.50	$ 0.93	$ 0.87
Diluted earnings per share (dollars per share)	$ 0.52	$ 0.49	$ 0.93	$ 0.86