Impact of Adopting ASC 606 (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended
	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Jan. 31, 2019	Jan. 31, 2018	May 01, 2018	Apr. 30, 2018	Apr. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of changes in accounting standards (Note 1)									$ (5)
Sales	$ 1,181			$ 1,156			$ 3,329	$ 3,251
Excise taxes	277			278			749	736
Net sales	904			878			2,580	2,515
Cost of sales	333			291			896	825
Gross profit	571			587			1,684	1,690
Advertising expenses	103			112			303	308
Selling, general, and administrative expenses	149			173			478	496
Other expense (income), net	(1)			(4)			(13)	(15)
Operating income	320			306			916	901
Non-operating postretirement expense	15			2			19	7
Interest income	(2)			(2)			(6)	(4)
Interest expense	23			17			67	49
Income before income taxes	284			289			836	849
Income taxes	57			99			160	242
Net income	$ 227	$ 249	$ 200	$ 190	$ 239	$ 178	$ 676	$ 607
Basic earnings per share (dollars per share)	$ 0.47			$ 0.39			$ 1.41	$ 1.26
Diluted earnings per share (dollars per share)	$ 0.47			$ 0.39			$ 1.40	$ 1.25
Other current assets	$ 287						$ 287			$ 298
Deferred tax assets	20						20			16
Assets	5,163						5,163			4,976
Accounts payable and accrued expenses	587						587			581
Accrued income taxes	22						22			25
Deferred tax liabilities	119						119			85
Liabilities	3,670						3,670			3,660
Retained earnings	2,085						2,085			1,730
Stockholders' Equity Attributable to Parent	1,493	$ 1,497	$ 1,368	$ 1,201	$ 1,647	$ 1,420	1,493	$ 1,201		$ 1,316	$ 1,370
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of changes in accounting standards (Note 1)									$ (25)
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sales	3						(15)
Excise taxes	0						0
Net sales	3						(15)
Cost of sales	0						0
Gross profit	3						(15)
Advertising expenses	(2)						(10)
Selling, general, and administrative expenses	0						(2)
Other expense (income), net	0						0
Operating income	5						(3)
Non-operating postretirement expense	0						0
Interest income	0						0
Interest expense	0						0
Income before income taxes	5						(3)
Income taxes	1						(1)
Net income	$ 4						$ (2)
Basic earnings per share (dollars per share)	$ 0.01						$ 0.00
Diluted earnings per share (dollars per share)	$ 0.01						$ 0.00
Other current assets	$ (1)						$ (1)
Deferred tax assets	1						1
Assets	0						0
Accounts payable and accrued expenses	34						34
Deferred tax liabilities	(7)						(7)
Liabilities	27						27
Retained earnings	(27)						(27)
Stockholders' Equity Attributable to Parent	(27)						(27)
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sales	1,178						3,344
Excise taxes	277						749
Net sales	901						2,595
Cost of sales	333						896
Gross profit	568						1,699
Advertising expenses	105						313
Selling, general, and administrative expenses	149						480
Other expense (income), net	(1)						(13)
Operating income	315						919
Non-operating postretirement expense	15						19
Interest income	(2)						(6)
Interest expense	23						67
Income before income taxes	279						839
Income taxes	56						161
Net income	$ 223						$ 678
Basic earnings per share (dollars per share)	$ 0.46						$ 1.41
Diluted earnings per share (dollars per share)	$ 0.46						$ 1.40
Other current assets	$ 288						$ 288
Deferred tax assets	19						19
Assets	5,163						5,163
Accounts payable and accrued expenses	553						553
Deferred tax liabilities	126						126
Liabilities	3,643						3,643
Retained earnings	2,112						2,112
Stockholders' Equity Attributable to Parent	$ 1,520						$ 1,520