SEPARATION TRANSACTION - Transition Services and Supply Agreement Narrative (Details) - WK Kellogg Co - Spinoff - USD ($) $ in Millions	3 Months Ended
Mar. 29, 2025	Mar. 30, 2024
Transition Services Agreement (TSA)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Intra-Entity Amounts, Discontinued Operation after Disposal, Expense	$ 14	$ 47
Discontinued Operation, Period of Continuing Involvement after Disposal	2 years
Transition Services Agreement (TSA) \| COGS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Intra-Entity Amounts, Discontinued Operation after Disposal, Expense	$ 6	33
Transition Services Agreement (TSA) \| Selling, General and Administrative Expenses
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Intra-Entity Amounts, Discontinued Operation after Disposal, Expense	$ 8	14
Supply Agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Period of Continuing Involvement after Disposal	3 years
Supply Agreement \| Sales
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Intra-Entity Amounts, Discontinued Operation after Disposal, Revenue	$ 8	15
Supply Agreement \| COGS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Intra-Entity Amounts, Discontinued Operation after Disposal, Expense	$ 7	$ 13

Amount of expense in continuing operations related to continuing involvement in a discontinued operation after the disposal that before the disposal was eliminated as intra-entity transactions.

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-Topic 205
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-Topic 360
-SubTopic 10
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