Stockholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Oct. 31, 2021	Jul. 31, 2021	Oct. 31, 2020	Jul. 31, 2020	Oct. 31, 2021	Oct. 31, 2020
Beginning balance	$ 2,683	$ 2,656	$ 2,150	$ 1,975	$ 2,656	$ 1,975
Net income	236	192	240	324	428	564
Net other comprehensive income (loss)	2	8	15	24	10	39
Declaration of cash dividends		(172)		(167)
Stock-based compensation expense	3	4	3	3
Stock issued under compensation plans	1	5	5	10
Loss on issuance of treasury stock issued under compensation plans	(2)	(10)	(10)	(19)
Ending balance	2,923	2,683	2,403	2,150	2,923	2,403
Additional Paid-in Capital [Member]
Beginning balance	2	0	0	0	0	0
Stock-based compensation expense	3	4	3	3
Loss on issuance of treasury stock issued under compensation plans	(2)	(2)	(3)	(3)
Ending balance	3	2	0	0	3	0
Retained Earnings [Member]
Beginning balance	3,255	3,243	2,849	2,708	3,243	2,708
Net income	236	192	240	324
Declaration of cash dividends		(172)		(167)
Loss on issuance of treasury stock issued under compensation plans	0	(8)	(7)	(16)
Ending balance	3,491	3,255	3,082	2,849	3,491	3,082
AOCI Attributable to Parent [Member]
Beginning balance	(414)	(422)	(523)	(547)	(422)	(547)
Net other comprehensive income (loss)	2	8	15	24
Ending balance	(412)	(414)	(508)	(523)	(412)	(508)
Treasury Stock, Common [Member]
Beginning balance	(232)	(237)	(248)	(258)	(237)	(258)
Stock issued under compensation plans	1	5	5	10
Ending balance	(231)	(232)	(243)	(248)	(231)	(243)
Common stock, Class A, voting [Member] | Common Stock [Member]
Beginning balance	25	25	25	25	25	25
Ending balance	25	25	25	25	25	25
Common stock, Class B, nonvoting [Member] | Common Stock [Member]
Beginning balance	47	47	47	47	47	47
Ending balance	$ 47	$ 47	$ 47	$ 47	$ 47	$ 47