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)					1
Common stock repurchases	(50)				$ (50)		(50)
Net income	1,043			1,040			1,040	3
Acquisition of noncontrolling interest-Multipro	552						0	552
Dividends declared	(374)			(374)			(374)
Distributions to Noncontrolling interest	(1)						0	(1)
Other comprehensive income (loss)	(48)					(44)	(44)	(4)
Stock compensation	30		30	0			30
Stock options exercised and other (in shares)					(2)
Stock options exercised and other	58		(42)	8	$ 92		58
Balance (in shares) at Jun. 30, 2018		421			74
Balance at Jun. 30, 2018		$ 105	866	7,743	$ (4,375)	(1,501)	2,838	566
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,554
Balance at Mar. 31, 2018		$ 105	852	7,334	$ (4,346)	(1,407)	2,538	16
Balance (in shares) at Mar. 31, 2018		421			74
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock repurchases (in shares)					1
Common stock repurchases	(50)				$ (50)		(50)
Net income	599			596			596	3
Acquisition of noncontrolling interest-Multipro	552						0	552
Dividends declared	(187)			(187)			(187)
Distributions to Noncontrolling interest	(1)						0	(1)
Other comprehensive income (loss)	(98)					(94)	(94)	(4)
Stock compensation	14		14				14
Stock options exercised and other (in shares)					(1)
Stock options exercised and other	21		0	0	$ 21		21
Balance (in shares) at Jun. 30, 2018		421			74
Balance at Jun. 30, 2018		$ 105	866	7,743	$ (4,375)	(1,501)	2,838	566
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	3,404
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]
Reclassification of tax effects relating to U.S. tax reform				22
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
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	577			568			568	9
Sale of subsidiary shares to noncontrolling interest	1						0	1
Dividends declared	(380)			(380)			(380)
Distributions to Noncontrolling interest	(9)						0	(9)
Other comprehensive income (loss)	56					53	53	3
Reclassification of tax effects relating to U.S. tax reform	0			22		(22)	0
Stock compensation	29		29				29
Stock options exercised and other (in shares)					(1)
Stock options exercised and other	(1)		(29)	(4)	$ 32		(1)
Balance (in shares) at Jun. 29, 2019		421			80
Balance at Jun. 29, 2019	2,650	$ 105	895	7,858	$ (4,739)	(1,469)	2,650	562
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	3,097
Balance at Mar. 30, 2019		$ 105	877	7,762	$ (4,744)	(1,467)	2,533	564
Balance (in shares) at Mar. 30, 2019		421			80
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	292			286			286	6
Sale of subsidiary shares to noncontrolling interest	1						0	1
Dividends declared	(188)			(188)			(188)
Distributions to Noncontrolling interest	(9)						0	(9)
Other comprehensive income (loss)	(2)					(2)	(2)
Stock compensation	16		16				16
Stock options exercised and other (in shares)					0
Stock options exercised and other	5		2	(2)	$ 5		5
Balance (in shares) at Jun. 29, 2019		421			80
Balance at Jun. 29, 2019	2,650	$ 105	$ 895	$ 7,858	$ (4,739)	$ (1,469)	$ 2,650	$ 562
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 3,212