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SEPARATION TRANSACTION - Transition Services and Supply Agreement Narrative (Details) - WK Kellogg Co - Spinoff - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 28, 2025	Jun. 29, 2024	Jun. 28, 2025	Jun. 29, 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		$ 44	$ 16	$ 91
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		29	7	62
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	9	29
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	$ 10	11	18	26
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	$ 9	$ 10	$ 16	$ 23