RESTRUCTURING - Restructuring Liability Rollforward (Details) - USD ($)	12 Months Ended
	Dec. 28, 2024	Dec. 30, 2023	Dec. 31, 2022
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	$ 0
Restructuring charge	56,000,000	$ 0	$ 0
Cash payments	(1,000,000)
Non-cash charges and other	(34,000,000)
Restructuring reserve, ending balance	21,000,000	0
Employee Related Costs
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	0
Restructuring charge	20,000,000	0	0
Cash payments	0
Non-cash charges and other	0
Restructuring reserve, ending balance	20,000,000	0
Pension curtailment (gain) loss, net
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	0
Restructuring charge	3,000,000	0	0
Cash payments	0
Non-cash charges and other	(3,000,000)
Restructuring reserve, ending balance	0	0
Asset related costs
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	0
Restructuring charge	31,000,000	0	0
Cash payments	0
Non-cash charges and other	(31,000,000)
Restructuring reserve, ending balance	0	0
Other cost
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	0
Restructuring charge	2,000,000	0	$ 0
Cash payments	(1,000,000)
Non-cash charges and other	0
Restructuring reserve, ending balance	$ 1,000,000	$ 0

WK Kellogg Co 10-K/A