CONSOLIDATED STATEMENT OF EQUITY (unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common stock	Net Kellanova investment	Capital in excess of par value	Retained earnings	Accumulated other comprehensive income (loss)
Balance at Dec. 31, 2022	$ 687		$ 725	$ 0	$ 0	$ (38)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	95		95
Net transfer (to)/from Kellanova	74		66			8
Distribution of WK Kellogg Co shares to Kellanova shareholders	(663)		(663)
Other comprehensive income (loss)	3					3
Balance at Sep. 30, 2023	196		223	0	0	(27)
Balance at Jul. 01, 2023	650		684	0	0	(34)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	42		42
Net transfer (to)/from Kellanova	168		160			8
Distribution of WK Kellogg Co shares to Kellanova shareholders	(663)		(663)
Other comprehensive income (loss)	(1)					(1)
Balance at Sep. 30, 2023	196		$ 223	0	0	(27)
Balance (in shares) at Dec. 30, 2023		86
Balance at Dec. 30, 2023	300	$ 0		327	1	(28)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	53				53
Dividends declared ($0.16 per share)	(41)				(41)
Other comprehensive income (loss)	(8)					(8)
Stock compensation	9			11	(2)
Share issuance	3			3
Balance (in shares) at Sep. 28, 2024		86
Balance at Sep. 28, 2024	$ 316	$ 0		341	11	(36)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared (in dollars per share)	$ 0.48
Balance (in shares) at Jun. 29, 2024		86
Balance at Jun. 29, 2024	$ 336	$ 0		335	37	(36)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(11)				(11)
Dividends declared ($0.16 per share)	(14)				(14)
Other comprehensive income (loss)	0					0
Stock compensation	4			5	(1)
Share issuance	1			1
Balance (in shares) at Sep. 28, 2024		86
Balance at Sep. 28, 2024	$ 316	$ 0		$ 341	$ 11	$ (36)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared (in dollars per share)	$ 0.16