Sale of Accounts Receivable - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 29, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017	Dec. 30, 2017	Jul. 31, 2016
Receivables Sales Agreement
Transfer of Financial Assets Accounted for as Sales [Line Items]
Gain (Loss) on Sale of Accounts Receivable	$ (7)		$ (3)	$ (20)	$ (8)
Receivables Sales Agreement | Maximum [Member]
Transfer of Financial Assets Accounted for as Sales [Line Items]
Transfers of Accounts Receivable Agreements	1,033	$ 988		1,033
Receivables Sales Agreement | Sold And Outstanding
Transfer of Financial Assets Accounted for as Sales [Line Items]
Transfer of Financial Assets Accounted for as Sales, Amount Derecognized	942			942		$ 601
Kellogg Funding Company Program
Transfer of Financial Assets Accounted for as Sales [Line Items]
Cash Proceeds Received for Assets Derecognized						412
Deferred Purchase Price		$ 21				21
Kellogg Funding Company Program | Maximum [Member]
Transfer of Financial Assets Accounted for as Sales [Line Items]
Transfers of Accounts Receivable Agreements							$ 600
Kellogg Funding Company Program | Sold And Outstanding
Transfer of Financial Assets Accounted for as Sales [Line Items]
Transfer of Financial Assets Accounted for as Sales, Amount Derecognized						433
Kellogg Foreign Subsidiaries Other Program
Transfer of Financial Assets Accounted for as Sales [Line Items]
Transfers of Accounts Receivable Agreements	$ 23			$ 23		$ 86