Stockholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	May 01, 2018
Balance at April 30, 2018	$ 1,316
Cumulative effect of changes in accounting standards (Note 1)			$ (5)
Net income	200	$ 178
Net other comprehensive income (loss)	14	$ 14
Cash dividends	(152)
Acquisition of treasury stock	(6)
Stock-based compensation expense	5
Stock issued under compensation plans	9
Loss on issuance of treasury stock issued under compensation plans	(13)
Balance at July 31, 2018	1,368
Additional Paid-in Capital [Member]
Balance at April 30, 2018	4
Stock-based compensation expense	5
Loss on issuance of treasury stock issued under compensation plans	(7)
Balance at July 31, 2018	2
Retained Earnings [Member]
Balance at April 30, 2018	1,730
Cumulative effect of changes in accounting standards (Note 1)			$ (5)
Net income	200
Cash dividends	(152)
Loss on issuance of treasury stock issued under compensation plans	(6)
Balance at July 31, 2018	1,767
AOCI Attributable to Parent [Member]
Balance at April 30, 2018	(378)
Net other comprehensive income (loss)	14
Balance at July 31, 2018	(364)
Treasury Stock, Common [Member]
Balance at April 30, 2018	(112)
Acquisition of treasury stock	(6)
Stock issued under compensation plans	9
Balance at July 31, 2018	(109)
Common stock, Class A, voting [Member] | Common Stock [Member]
Balance at April 30, 2018	25
Balance at July 31, 2018	25
Common stock, Class B, nonvoting [Member] | Common Stock [Member]
Balance at April 30, 2018	47
Balance at July 31, 2018	$ 47