STOCK COMPENSATION - Summary of Share-based Compensation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Dec. 30, 2023	Dec. 31, 2022	Jan. 01, 2022
Share-Based Payment Arrangement [Abstract]
Outstanding, beginning of period - shares	10	15	14
Granted - shares	0	0	3
Exercised - shares	(1)	(4)	(1)
Forfeitures and expirations	(1)	(1)	(1)
Awards transferred to WK Kellogg Co.	(1)
Adjustment for spin-off	2
Outstanding, end of period - shares	9	10	15
Exerciseable, end of period - shares	8	8	10
Outstanding, beginning of period - weighted-average exercise price	$ 65	$ 64	$ 65
Granted - weighted-average exercise price	0	0	58
Exercised - weighted-average exercise price	59	61	56
Forfeitures and expirations - weighted-average exercise price	60	63	66
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Awards transferred to spin off, Weighted Average Exercise Price	66
Outstanding, end of period - weighted-average exercise price	55	65	64
Exercisable, end of period - weighted-average exercise price	$ 59	$ 67	$ 66
Outstanding, end of period - weighted-average remaining contractual term (years)	4 years 6 months
Excerciseable, end of period - weighted-average remaining contractual term (years)	4 years 3 months 18 days
Outstanding, end of period - aggregate intrinsic value	$ 15
Exerciseable, end of period - aggregate intrinsic value	12
Total intrinsic value of options exercised	5	$ 44	$ 6
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Incremental Expense related to spin-off	10
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Incremental Expense related to spin-off	10
WK Kellogg Co
Share-Based Payment Arrangement [Abstract]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Incremental Expense related to spin-off	9
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Incremental Expense related to spin-off	$ 9

Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Adjustment for spin-off

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Weighted average price of options that were either forfeited or expired.

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