Accounting policies - Allocation of Expenses from Parent (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 29, 2024	Jul. 01, 2023	Jun. 29, 2024	Jul. 01, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cost of goods sold	$ 476	$ 509	$ 980	$ 1,048
Selling, general and administrative expense	$ 149	163	$ 306	318
Kellanova
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cost of goods sold		34		89
Selling, general and administrative expense		89		174
Other (income) expense, net		(5)		(11)
Total		$ 118		$ 252

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.

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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The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(2)(d))
-Publisher FASB
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-Topic 220
-SubTopic 10
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-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(2)(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 924
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-Publisher FASB
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Total costs of sales and operating expenses for the period.

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The aggregate total costs related to selling a firm's product and services, as well as all other general and administrative expenses. Direct selling expenses (for example, credit, warranty, and advertising) are expenses that can be directly linked to the sale of specific products. Indirect selling expenses are expenses that cannot be directly linked to the sale of specific products, for example telephone expenses, Internet, and postal charges. General and administrative expenses include salaries of non-sales personnel, rent, utilities, communication, etc.

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