Accounting policies -Components of net parent investment (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 30, 2024	Apr. 01, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Stock compensation	$ 1	$ 1
Postretirement plan benefit	$ 9	7
Net transfer (to)/from Kellanova		(36)
Kellanova
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Net transfers (to) from Kellanova		(30)
Stock compensation		1
Postretirement plan benefit		(7)
Net transfer (to)/from Kellanova		$ (36)

Transfers (To) From Parent, Net

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- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 808
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479402/808-10-50-1

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- Definition

Amount of noncash expense (reversal of expense) for pension and other postretirement benefits.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

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- Definition

Amount of noncash expense for share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (a)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

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- Definition

The change in equity as a result of a spin-off transaction (a regular or reverse spin-off) which is based on the recorded amounts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 505
-SubTopic 60
-Section 25
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481423/505-60-25-2

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