Cover Page Document - USD ($) $ / shares in Units, $ in Billions	12 Months Ended
	Dec. 28, 2019	Jan. 25, 2020	Jun. 29, 2019
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 28, 2019
Document Transition Report	false
Entity File Number	1-4171
Entity Registrant Name	Kellogg Company
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	38-0710690
Entity Address, Address Line One	One Kellogg Square
Entity Address, City or Town	Battle Creek
Entity Address, State or Province	MI
Entity Address, Postal Zip Code	49016-3599
City Area Code	269
Local Phone Number	961-2000
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 14.7
Entity Common Stock, Shares Outstanding		342,054,365
Documents Incorporated by Reference [Text Block]	Parts of the registrant’s Proxy Statement for the Annual Meeting of Shareowners to be held on April 24, 2020 are incorporated by reference into Part III of this Report.
Closing price per share of common stock			$ 53.57
Amendment Flag	false
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2019
Entity Central Index Key	0000055067
Current Fiscal Year End Date	--12-28
Common stock
Entity Information [Line Items]
Title of 12(b) Security	Common Stock, $.25 par value per share
Trading Symbol	K
Security Exchange Name	NYSE
1.750% Senior Notes Due 2021
Entity Information [Line Items]
Title of 12(b) Security	1.750% Senior Notes due 2021
Trading Symbol	K 21
Security Exchange Name	NYSE
0.800% Senior Notes Due 2022
Entity Information [Line Items]
Title of 12(b) Security	0.800% Senior Notes due 2022
Trading Symbol	K 22A
Security Exchange Name	NYSE
1.000% Senior Notes Due 2024
Entity Information [Line Items]
Title of 12(b) Security	1.000% Senior Notes due 2024
Trading Symbol	K 24
Security Exchange Name	NYSE
1.250% Senior Notes Due 2025
Entity Information [Line Items]
Title of 12(b) Security	1.250% Senior Notes due 2025
Trading Symbol	K 25
Security Exchange Name	NYSE