Impact of Adopting ASC 606 (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended
	Oct. 31, 2018	Jul. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Oct. 31, 2018	Oct. 31, 2017	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	$ 1,161		$ 1,166		$ 2,148	$ 2,095
Excise taxes	251		252		472	458
Net sales	910		914		1,676	1,637
Cost of sales	320		304		563	534
Gross profit	590		610		1,113	1,103
Advertising expenses	102		109		200	196
Selling, general, and administrative expenses	161		162		329	323
Other expense (income), net	(5)		(10)		(12)	(11)
Operating income	332		349		596	595
Non-operating postretirement expense	2		3		4	5
Interest income	(2)		(1)		(4)	(2)
Interest expense	22		16		44	32
Income before income taxes	310		331		552	560
Income taxes	61		92		103	143
Net income	$ 249	$ 200	$ 239	$ 178	$ 449	$ 417
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
Other current assets	$ 305				$ 305			$ 298
Deferred tax assets	16				16			16
Assets	5,149				5,149			4,976
Accounts payable and accrued expenses	620				620			581
Accrued income taxes	17				17			25
Deferred tax liabilities	113				113			85
Liabilities	3,652				3,652			3,660
Retained earnings	2,016				2,016			1,730
Stockholders' Equity Attributable to Parent	1,497	$ 1,368	$ 1,647	$ 1,420	1,497	$ 1,647		$ 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	(8)				(18)
Excise taxes	0				0
Net sales	(8)				(18)
Cost of sales	0				0
Gross profit	(8)				(18)
Advertising expenses	(5)				(8)
Selling, general, and administrative expenses	(1)				(2)
Other expense (income), net	0				0
Operating income	(2)				(8)
Non-operating postretirement expense	0				0
Interest income	0				0
Interest expense	0				0
Income before income taxes	(2)				(8)
Income taxes	0				(2)
Net income	$ (2)				$ (6)
Basic earnings per share (dollars per share)	$ 0.00				$ (0.01)
Diluted earnings per share (dollars per share)	$ 0.00				$ (0.01)
Other current assets	$ (1)				$ (1)
Deferred tax assets	1				1
Assets	0				0
Accounts payable and accrued expenses	40				40
Deferred tax liabilities	(9)				(9)
Liabilities	31				31
Retained earnings	(31)				(31)
Stockholders' Equity Attributable to Parent	(31)				(31)
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sales	1,169				2,166
Excise taxes	251				472
Net sales	918				1,694
Cost of sales	320				563
Gross profit	598				1,131
Advertising expenses	107				208
Selling, general, and administrative expenses	162				331
Other expense (income), net	(5)				(12)
Operating income	334				604
Non-operating postretirement expense	2				4
Interest income	(2)				(4)
Interest expense	22				44
Income before income taxes	312				560
Income taxes	61				105
Net income	$ 251				$ 455
Basic earnings per share (dollars per share)	$ 0.52				$ 0.94
Diluted earnings per share (dollars per share)	$ 0.52				$ 0.94
Other current assets	$ 306				$ 306
Deferred tax assets	15				15
Assets	5,149				5,149
Accounts payable and accrued expenses	580				580
Deferred tax liabilities	122				122
Liabilities	3,621				3,621
Retained earnings	2,047				2,047
Stockholders' Equity Attributable to Parent	$ 1,528				$ 1,528