DISCONTINUED OPERATIONS (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
	Sep. 29, 2023	Dec. 30, 2023	Sep. 30, 2023	Jul. 01, 2023	Apr. 01, 2023	Dec. 31, 2022	Oct. 01, 2022	Jul. 02, 2022	Apr. 02, 2022	Dec. 30, 2023	Dec. 31, 2022	Jan. 01, 2022
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Net Sales										$ 2,085	$ 2,662	$ 2,434
Disposal Group, Including Discontinued Operation, Costs of Goods Sold										1,387	1,858	1,692
Disposal Group, Including Discontinued Operation, General and Administrative Expense										479	381	373
Disposal Group, Including Discontinued Operation, Operating Profit										219	423	369
Disposal Group, Including Discontinued Operation, Interest Expense										26	17	18
Disposal Group, Including Discontinued Operation, Other Income										54		162
Disposal Group, Including Discontinued Operation, Other Expense											(111)
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax										247	295	513
Discontinued Operation, Tax Effect of Discontinued Operation										71	64	121
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent										176	231	392
Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents						$ 0					0
Disposal Group, Including Discontinued Operation, Accounts Receivable, Net						204					204
Disposal Group, Including Discontinued Operation, Inventories						429					429
Disposal Group, Including Discontinued Operation, Other Assets, Current						5					5
Current assets of discontinued operations		$ 0				638				0	638
Disposal Group, Including Discontinued Operation, Property, Noncurrent						699					699
Disposal Group Including Discontinued Operation Operating Lease Right-of-Use Assets						7					7
Disposal Group, Including Discontinued Operation, Goodwill, Noncurrent						305					305
Disposal Group, Including Discontinued Operation, Other Intangibles, Noncurrent						57					57
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent						210					210
Total assets of discontinued operations						1,916					1,916
Disposal Group, Including Discontinued Operation, Accounts Payable, Current						405					405
Disposal Operating Lease, Liability, Current						3					3
Disposal Group, Including Discontinued Operation, Accrued Advertising and Promotion, Current						57					57
Disposal Group, Including Discontinued Operation, Accrued salaries and wages, Current						52					52
Disposal Group, Including Discontinued Operation, Other Liabilities, Current						31					31
Current liabilities of discontinued operations		0				548				0	548
Disposal Group, Including Discontinued Operation, Operating Lease, Liability, Noncurrent						4					4
Disposal Group, Including Discontinued Operation, Deferred Income Tax Liabilities						53					53
Disposal Group, Including Discontinued Operation, Pension Plan Liabilities						116					116
Disposal Group, Including Discontinued Operation, Other Liabilities, Noncurrent						10					10
Disposal Group, Including Discontinued Operation, Liabilities						731					731
Disposal Group, Including Discontinued Operation, Depreciation and Amortization										52	74	72
Capital Expenditure, Discontinued Operations										107	87	90
Disposal Group, Including Discontinued Operation, Postretirement benefit plan expense (benefit)										(53)	123	(143)
Disposal Group, Including Discontinued Operation, Transition Services Agreement Cost										52
Net sales		3,174	$ 3,255	$ 3,351	$ 3,342	3,164	$ 3,251	$ 3,181	$ 3,057	13,122	12,653	11,747
Cost of goods sold										8,839	8,842	$ 7,929
WK Kellogg Co
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net sales										18
Cost of goods sold										16
SGA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Transition Services Agreement Cost										15
Cost of Goods and Service, Product and Service Benchmark
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Transition Services Agreement Cost										37
2.65% U.S. Dollar Notes Due 2023
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt instrument, stated interest rate	2.65%
Long-term Debt, Gross	$ 550	$ 0				$ 547				$ 0	$ 547
Revolving Credit Facility | Line of Credit | WK Kellogg Co
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt, Long-Term and Short-Term, Combined Amount	664
Payments of Dividends	$ 663