Quarterly Financial Data Net income and earnings per share (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Net income (loss) attributable to Kellogg Company, Basic	$ 428	$ 297	$ 282	$ 262	$ (53)	$ 292	$ 280	$ 175	$ 1,269	$ 694	$ 614
Basic	$ 1.24	$ 0.86	$ 0.81	$ 0.75	$ (0.15)	$ 0.83	$ 0.80	$ 0.50	$ 3.65	$ 1.98	$ 1.74
Diluted	$ 1.23	$ 0.85	$ 0.80	$ 0.74	$ (0.15)	$ 0.82	$ 0.79	$ 0.49	$ 3.62	$ 1.96	$ 1.72