STOCK COMPENSATION - Summary of Share-based Compensation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		12 Months Ended
		Dec. 28, 2024	Dec. 30, 2023		Dec. 31, 2022		Apr. 01, 2023
Share-Based Payment Arrangement [Abstract]
Outstanding, beginning of period - shares	[1]	9	10		15
Granted - shares		0	0		0
Exercised - shares		(3)	(1)		(4)
Forfeitures and expirations		0	(1)		(1)
Awards transferred to WK Kellogg Co.			(1)		0
Adjustment for spin-off			2	[2]	0
Outstanding, end of period - shares		6	9	[1]	10	[1]
Exerciseable, end of period - shares		6	8		8
Outstanding, beginning of period - weighted-average exercise price	[1]	$ 58	$ 65		$ 64
Granted - weighted-average exercise price		0	0		0
Exercised - weighted-average exercise price		59	59		61
Forfeitures and expirations - weighted-average exercise price		0	60		63
Awards transferred to WK Kellogg Co			66		0
Outstanding, end of period - weighted-average exercise price		57	58	[1]	65	[1]
Exercisable, end of period - weighted-average exercise price		$ 57	$ 58		$ 67
Outstanding, end of period - weighted-average remaining contractual term (years)		4 years
Excerciseable, end of period - weighted-average remaining contractual term (years)		4 years
Outstanding, end of period - aggregate intrinsic value		$ 130
Exerciseable, end of period - aggregate intrinsic value		130
Total intrinsic value of options exercised		$ 36	$ 5		$ 44
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
2023 Performance Share Award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, beginning of year - weighted-average grant date fair value							$ 60
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

[1] Activities prior to the spin-off remain unadjusted to ensure consistency with historical reporting.

[2] In connection with the spin-off of WK Kellogg Co, the modification of stock options resulted in incremental expense totaling approximately $10 million, of which $9 million was related to vested awards and was recognized immediately. The remaining expense will be amortized over the vesting period of the award.