Reportable Segments Supplemental Product Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 02, 2021	Sep. 26, 2020	Oct. 02, 2021	Sep. 26, 2020
Segment Reporting Information [Line Items]
Net sales	$ 3,622	$ 3,429	$ 10,761	$ 10,306
Snacks
Segment Reporting Information [Line Items]
Net sales	1,712	1,593	5,015	4,669
Cereal
Segment Reporting Information [Line Items]
Net sales	1,313	1,324	4,023	4,093
Frozen
Segment Reporting Information [Line Items]
Net sales	277	279	841	857
Noodles and other
Segment Reporting Information [Line Items]
Net sales	$ 320	$ 233	$ 882	$ 687