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	$ 3,159
Balance at Dec. 29, 2018		$ 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	285			282			282	3
Dividends declared	(192)			(192)			(192)
Other comprehensive income (loss)	58					55	55	3
Reclassification of tax effects relating to U.S. tax reform	0			22		(22)	0
Stock compensation	13		13				13
Stock options exercised and other (in shares)					(1)
Stock options exercised and other	(6)		(31)	(2)	$ 27		(6)
Balance (in shares) at Mar. 30, 2019		421			80
Balance at Mar. 30, 2019		$ 105	877	7,762	$ (4,744)	(1,467)	2,533	564
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	3,097
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	3,314
Balance at Dec. 28, 2019	2,747	$ 105	921	7,859	$ (4,690)	(1,448)	2,747	567
Balance (in shares) at Dec. 28, 2019		421			79
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	350			347			347	3
Dividends declared	(195)			(195)			(195)
Other comprehensive income (loss)	(311)					(279)	(279)	(32)
Stock compensation	19		19				19
Stock options exercised and other (in shares)					(1)
Stock options exercised and other	35		(29)	(1)	$ 65		35
Balance (in shares) at Mar. 28, 2020		421			78
Balance at Mar. 28, 2020	2,674	$ 105	$ 911	$ 8,010	$ (4,625)	$ (1,727)	$ 2,674	$ 538
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 3,212