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)					0
Common stock repurchases	0				$ 0		0
Net income	444			444			444
Dividends	(187)			(187)			(187)
Other comprehensive income (loss)	50					50	50	0
Stock compensation	16		16				16
Stock options exercised and other (in shares)					(1)
Stock options exercised and other	37		(42)	8	$ 71		37
Balance (in shares) at Mar. 31, 2018		421			74
Balance at Mar. 31, 2018	2,538	$ 105	$ 852	$ 7,334	$ (4,346)	$ (1,407)	$ 2,538
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 2,554							$ 16