Multipemployer Pension and Postretirement Plans Multiemployer Pension Plans Trusts Funds Contributions (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Multiemployer Plans [Line Items]
Collective-Bargaining Arrangement, percentage of total contributions	5.00%
Multiemployer withdrawal obligation annual cash obligation	$ 8
Multiemployer Plans, Withdrawal Obligation	$ 156	$ 32
Multiemployer plan withdrawal obligation term	20 years
Multiemployer withdrawal liability payments	$ 8	3
Project K
Multiemployer Plans [Line Items]
Multiemployer plan withdrawal expense	$ 132	$ 7	$ 26

Annual cash payments associated with multi-employer pension plan withdrawal obligation.

No definition available.

Name:	k_AnnualCashObligation
Namespace Prefix:	k_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Costs associated with exiting Multiemployer plans.

+ References

No definition available.

+ Details

Name:	k_MultiemployerPlanWithdrawalExpense
Namespace Prefix:	k_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Multiemployer plan withdrawal obligation term.

+ References

No definition available.

+ Details

Name:	k_MultiemployerPlanWithdrawalObligationTerm
Namespace Prefix:	k_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Cash payments for Multiemployer withdrawal obligations.

+ References

No definition available.

+ Details

Name:	k_MultiemployerWithdrawalLiabilityPayments
Namespace Prefix:	k_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of contributions required of employer under collective bargaining arrangement to total contributions required under all collective bargaining arrangements for pension and other postretirement plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947

+ Details

Name:	us-gaap_MultiemployerPlanCollectiveBargainingArrangementPercentageOfContributionsRequiredForMultipleCollectiveBargainingArrangements
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_MultiemployerPlansLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the obligation recognized by withdrawing from a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

+ References

No definition available.

+ Details

Name:	us-gaap_MultiemployerPlansWithdrawalObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_RestructuringPlanAxis=k_ProjectKMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: