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	$ 1,907							$ 16
Balance at Dec. 31, 2016		$ 105	$ 806	$ 6,552	$ (3,997)	$ (1,575)	$ 1,891
Balance (in shares) at Dec. 31, 2016		420			69
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock repurchases (in shares)					7
Common stock repurchases	(516)				$ (516)		(516)
Net income	1,254			1,254			1,254	0
Dividends	(736)			(736)			(736)
Other comprehensive income (loss)	118					118	118	0
Stock compensation	66		66				66
Stock options exercised and other (in shares)		1			(1)
Stock options exercised and other	101		6	(1)	$ 96		101
Balance (in shares) at Dec. 30, 2017		421			75
Balance at Dec. 30, 2017	2,178	$ 105	878	7,069	$ (4,417)	(1,457)	2,178
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 2,194							16
Common stock repurchases (in shares)	2				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	(569)			(568)			(568)	(1)
Other comprehensive income (loss)	(61)					(55)	(55)	(6)
Stock compensation	42		42				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	3,048	$ 105	$ 883	$ 7,929	$ (4,357)	$ (1,512)	$ 3,048
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 3,615							$ 567