Equity Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 30, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Oct. 01, 2016	Jul. 02, 2016	Apr. 02, 2016	Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Equity [Abstract]
Net income (loss) attributable to Kellogg Company, Basic	$ 428	$ 297	$ 282	$ 262	$ (53)	$ 292	$ 280	$ 175	$ 1,269	$ 694	$ 614
Net income attributed to Kellogg Company, Diluted									$ 1,269	$ 694	$ 614
Average shares outstanding, Basic (in shares)									348	350	354
Average shares outstanding, Dilutive potential common shares (in shares)									2	4	2
Average shares outstanding, Diluted (in shares)									350	354	356
Earnings per share, Basic (in shares)	$ 1.24	$ 0.86	$ 0.81	$ 0.75	$ (0.15)	$ 0.83	$ 0.80	$ 0.50	$ 3.65	$ 1.98	$ 1.74
Earnings per share, Dilutive potential common shares (in dollars per share)									(0.03)	(0.02)	(0.02)
Earnings per share, Diluted (in dollars per share)	$ 1.23	$ 0.85	$ 0.80	$ 0.74	$ (0.15)	$ 0.82	$ 0.79	$ 0.49	$ 3.62	$ 1.96	$ 1.72