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	1,056			1,046			1,046	10
Dividends, Common Stock	(586)			(586)			(586)
Distributions to noncontrolling interest	(1)						0	(1)
Other comprehensive income (loss)	(343)					(309)	(309)	(34)
Stock compensation	55		55				55
Stock options exercised and other	91		(28)	(1)	$ 120		91
Stock options exercised and other (in shares)					(2)
Balance (in shares) at Sep. 26, 2020		421			77
Balance at Sep. 26, 2020		$ 105	948	8,318	$ (4,570)	(1,757)	3,044	542
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Sep. 26, 2020	$ 3,586
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared - per share	$ 1.71
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, Beginning Balance at Jun. 27, 2020	$ 3,406
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	352			348			348	4
Dividends, Common Stock	(196)			(196)			(196)
Other comprehensive income (loss)	(38)					(40)	(40)	2
Stock compensation	18		18				18
Stock options exercised and other	44		1	0	$ 43		44
Stock options exercised and other (in shares)					(1)
Balance (in shares) at Sep. 26, 2020		421			77
Balance at Sep. 26, 2020		$ 105	948	8,318	$ (4,570)	(1,757)	3,044	542
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Sep. 26, 2020	$ 3,586
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	$ 1,061			1,055			1,055	6
Acquisition of noncontrolling interest and other	52		22				22	30
Dividends, Common Stock	(590)			(590)			(590)
Distributions to noncontrolling interest	(18)						0	(18)
Other comprehensive income (loss)	22					39	39	(17)
Stock compensation	50		50				50
Stock options exercised and other	36		(39)	5	$ 70		36
Stock options exercised and other (in shares)					(1)
Balance (in shares) at Oct. 02, 2021		421			80
Balance at Oct. 02, 2021	3,484	$ 105	1,005	8,796	$ (4,729)	(1,693)	3,484	525
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Oct. 02, 2021	$ 4,009
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared - per share	$ 1.73
Balance (in shares) at Jul. 03, 2021		421			80
Balance at Jul. 03, 2021		$ 105	973	8,688	$ (4,741)	(1,663)	3,362	518
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Jul. 03, 2021	$ 3,880
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	305			307			307	(2)
Acquisition of noncontrolling interest and other	52		22				22	30
Dividends, Common Stock	(198)			(198)			(198)
Distributions to noncontrolling interest	(17)						0	(17)
Other comprehensive income (loss)	(34)					(30)	(30)	(4)
Stock compensation	11		11				11
Stock options exercised and other	10		(1)	(1)	$ 12		10
Stock options exercised and other (in shares)					0
Balance (in shares) at Oct. 02, 2021		421			80
Balance at Oct. 02, 2021	3,484	$ 105	$ 1,005	$ 8,796	$ (4,729)	$ (1,693)	$ 3,484	$ 525
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Oct. 02, 2021	$ 4,009
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared - per share	$ 0.58