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SEPARATION TRANSACTION - Transition Services and Supply Agreement Narrative (Details) - WK Kellogg Co - Spinoff - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 27, 2025	Sep. 28, 2024	Sep. 27, 2025	Sep. 28, 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		$ 37	$ 18	$ 128
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		22	8	84
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		15	10	44
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	$ 7	9	25	35
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	$ 6	$ 7	$ 22	$ 30