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
Balance (in shares) at Dec. 28, 2019		421			79
Balance at Dec. 28, 2019		$ 105	$ 921	$ 7,859	$ (4,690)	$ (1,448)	$ 2,747	$ 567
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Dec. 28, 2019	$ 3,314
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	704			698			698	6
Dividends, Common Stock	(390)			(390)			(390)
Distributions to noncontrolling interest	(1)						0	(1)
Other comprehensive income (loss)	(305)					(269)	(269)	(36)
Stock compensation	37		37				37
Stock options exercised and other	47		(29)	(1)	$ 77		47
Stock options exercised and other (in shares)					(1)
Balance (in shares) at Jun. 27, 2020		421			78
Balance at Jun. 27, 2020		$ 105	929	8,166	$ (4,613)	(1,717)	2,870	536
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Jun. 27, 2020	$ 3,406
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared - per share	$ 1.14
Balance (in shares) at Mar. 28, 2020		421			78
Balance at Mar. 28, 2020		$ 105	911	8,010	$ (4,625)	(1,727)	2,674	538
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Mar. 28, 2020	$ 3,212
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	354			351			351	3
Dividends, Common Stock	(195)			(195)			(195)
Distributions to noncontrolling interest	(1)						0	(1)
Other comprehensive income (loss)	6					10	10	(4)
Stock compensation	18		18				18
Stock options exercised and other	12		0	0	$ 12		12
Stock options exercised and other (in shares)					0
Balance (in shares) at Jun. 27, 2020		421			78
Balance at Jun. 27, 2020		$ 105	929	8,166	$ (4,613)	(1,717)	2,870	536
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Jun. 27, 2020	$ 3,406
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared - per share	$ 0.57
Balance (in shares) at Jan. 02, 2021		421			77
Balance at Jan. 02, 2021	$ 3,112	$ 105	972	8,326	$ (4,559)	(1,732)	3,112	524
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Jan. 02, 2021	3,636
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock repurchased	$ (240)				$ (240)		(240)
Common stock repurchased (in shares)	4				4
Net income	$ 756			748			748	8
Dividends, Common Stock	(392)			(392)			(392)
Distributions to noncontrolling interest	(1)						0	(1)
Other comprehensive income (loss)	56					69	69	(13)
Stock compensation	39		39				39
Stock options exercised and other	26		(38)	6	$ 58		26
Stock options exercised and other (in shares)					(1)
Balance (in shares) at Jul. 03, 2021		421			80
Balance at Jul. 03, 2021	3,362	$ 105	973	8,688	$ (4,741)	(1,663)	3,362	518
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Jul. 03, 2021	$ 3,880
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared - per share	$ 1.15
Balance (in shares) at Apr. 03, 2021		421			81
Balance at Apr. 03, 2021		$ 105	954	8,506	$ (4,762)	(1,665)	3,138	517
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Apr. 03, 2021	$ 3,655
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	385			380			380	5
Dividends, Common Stock	(197)			(197)			(197)
Distributions to noncontrolling interest	(1)						0	(1)
Other comprehensive income (loss)	(1)					2	2	(3)
Stock compensation	19		19				19
Stock options exercised and other	20		0	(1)	$ 21		20
Stock options exercised and other (in shares)					(1)
Balance (in shares) at Jul. 03, 2021		421			80
Balance at Jul. 03, 2021	3,362	$ 105	$ 973	$ 8,688	$ (4,741)	$ (1,663)	$ 3,362	$ 518
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Jul. 03, 2021	$ 3,880
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared - per share	$ 0.58