Reportable segments (Details) $ in Millions	3 Months Ended		6 Months Ended
Reportable segments (Details) $ in Millions	Jun. 28, 2025 USD ($)	Jun. 29, 2024 USD ($)	Jun. 28, 2025 USD ($) segment	Jun. 29, 2024 USD ($)	Dec. 28, 2024 USD ($)
Segment Reporting [Abstract]
Number of operating segments \| segment			1
Number of reportable segments \| segment			1
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	$ 613	$ 672	$ 1,276	$ 1,379
Long-lived assets	824		824		$ 786
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	529	589	1,114	1,212
Long-lived assets	623		623		624
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	75	75	145	150
Long-lived assets	166		166		129
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	9	$ 8	17	$ 17
Long-lived assets	$ 35		$ 35		$ 33

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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+ Details

WK Kellogg Co 10-Q