Stockholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended
	Jul. 31, 2016	Jul. 31, 2015	May 01, 2016
Balance at April 30, 2016	$ 1,562
Cumulative effect of change in accounting principle (Note 1)			$ 10
Net income	144	$ 156
Net other comprehensive income (loss)	(52)	$ (4)
Cash dividends	(134)
Acquisition of treasury stock	(201)
Stock-based compensation expense	4
Stock issued under compensation plans	7
Loss on issuance of treasury stock issued under compensation plans	(10)
Stock split	0
Balance at July 31, 2016	1,330
Additional Paid-in Capital [Member]
Balance at April 30, 2016	114
Stock-based compensation expense	4
Loss on issuance of treasury stock issued under compensation plans	(10)
Stock split	(34)
Balance at July 31, 2016	74
Retained Earnings [Member]
Balance at April 30, 2016	4,065
Cumulative effect of change in accounting principle (Note 1)			$ 10
Net income	144
Cash dividends	(134)
Balance at July 31, 2016	4,085
AOCI Attributable to Parent [Member]
Balance at April 30, 2016	(350)
Net other comprehensive income (loss)	(52)
Balance at July 31, 2016	(402)
Treasury Stock, Common [Member]
Balance at April 30, 2016	(2,301)
Acquisition of treasury stock	(201)
Stock issued under compensation plans	7
Balance at July 31, 2016	(2,495)
Common stock, Class A, voting [Member] | Common Stock [Member]
Balance at April 30, 2016	13
Stock split	12
Balance at July 31, 2016	25
Common stock, Class B, nonvoting [Member] | Common Stock [Member]
Balance at April 30, 2016	21
Stock split	22
Balance at July 31, 2016	$ 43