Consolidated Statement of Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common stock	Capital in excess of par value	Retained earnings	Treasury stock	Accumulated other comprehensive income (loss)	Total Kellogg Company equity	Non-controlling interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 2,194
Balance at Dec. 30, 2017		$ 105	$ 878	$ 7,069	$ (4,417)	$ (1,457)	$ 2,178	$ 16
Balance (in shares) at Dec. 30, 2017		421			75
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock repurchases (in shares)					2
Common stock repurchases	(120)				$ (120)		(120)
Net income	1,426			1,420			1,420	6
Acquisition of noncontrolling interest-Multipro	552						0	552
Dividends declared	(568)			(568)			(568)
Distributions to Noncontrolling interest	(1)						0	(1)
Other comprehensive income (loss)	(61)					(55)	(55)	(6)
Stock compensation	42		42	0			42
Stock options exercised and other (in shares)					(3)
Stock options exercised and other	151		(37)	8	$ 180		151
Balance (in shares) at Sep. 29, 2018		421			74
Balance at Sep. 29, 2018		$ 105	883	7,929	$ (4,357)	(1,512)	3,048	567
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	3,404
Balance at Jun. 30, 2018		$ 105	866	7,743	$ (4,375)	(1,501)	2,838	566
Balance (in shares) at Jun. 30, 2018		421			74
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock repurchases (in shares)					1
Common stock repurchases	(70)				$ (70)		(70)
Net income	383			380			380	3
Acquisition of noncontrolling interest-Multipro	0						0	0
Dividends declared	(194)			(194)			(194)
Distributions to Noncontrolling interest	0						0	0
Other comprehensive income (loss)	(13)					(11)	(11)	(2)
Stock compensation	12		12				12
Stock options exercised and other (in shares)					(1)
Stock options exercised and other	93		5	0	$ 88		93
Balance (in shares) at Sep. 29, 2018		421			74
Balance at Sep. 29, 2018		$ 105	883	7,929	$ (4,357)	(1,512)	3,048	567
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	3,615
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	3,159
Balance at Dec. 29, 2018	2,601	$ 105	895	7,652	$ (4,551)	(1,500)	2,601	558
Balance (in shares) at Dec. 29, 2018		421			77
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock repurchases (in shares)					4
Common stock repurchases	(220)				$ (220)		(220)
Net income	825			815			815	10
Sale of subsidiary shares to noncontrolling interest	1						0	1
Dividends declared	(574)			(574)			(574)
Distributions to Noncontrolling interest	(9)						0	(9)
Other comprehensive income (loss)	40					39	39	1
Reclassification of tax effects relating to U.S. tax reform	0			22		(22)	0
Stock compensation	42		42				42
Stock options exercised and other (in shares)					(1)
Stock options exercised and other	24		(28)	(5)	$ 57		24
Balance (in shares) at Sep. 28, 2019		421			80
Balance at Sep. 28, 2019	2,727	$ 105	909	7,910	$ (4,714)	(1,483)	2,727	561
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	3,212
Balance at Jun. 29, 2019		$ 105	895	7,858	$ (4,739)	(1,469)	2,650	562
Balance (in shares) at Jun. 29, 2019		421			80
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	248			247			247	1
Sale of subsidiary shares to noncontrolling interest	0						0	0
Dividends declared	(194)			(194)			(194)
Distributions to Noncontrolling interest	0						0	0
Other comprehensive income (loss)	(16)					(14)	(14)	(2)
Stock compensation	13		13				13
Stock options exercised and other (in shares)					0
Stock options exercised and other	25		1	(1)	$ 25		25
Balance (in shares) at Sep. 28, 2019		421			80
Balance at Sep. 28, 2019	2,727	$ 105	$ 909	$ 7,910	$ (4,714)	$ (1,483)	$ 2,727	$ 561
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 3,288