Supplemental financial statement data - (Details) - USD ($) $ in Millions	Mar. 30, 2024	Dec. 30, 2023
Condensed Financial Statements, Captions [Line Items]
Trade receivables	$ 223	$ 225
Allowance for expected credit losses	0	0
Other receivables	21	19
Accounts receivable, net	244	244
Raw materials	47	49
Manufacturing supplies	53	53
Materials in process	20	15
Finished goods	208	228
Inventories	328	345
Property, cost	2,637	2,676
Accumulated depreciation	(1,902)	(1,937)
Property, net	735	739
Accounts payable	544	541
Obligations under Transition Services Agreement	17	52
Operating lease obligations	10	6
Income taxes payable	12	7
Other	51	40
Other current liabilities	90	105
Other Counterparty
Condensed Financial Statements, Captions [Line Items]
Accounts payable	537	502
Kellanova
Condensed Financial Statements, Captions [Line Items]
Accounts payable	$ 7	$ 39