Reportable Segments Supplemental Product Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 03, 2021	Jun. 27, 2020	Jul. 03, 2021	Jun. 27, 2020
Segment Reporting Information [Line Items]
Net sales	$ 3,555	$ 3,465	$ 7,139	$ 6,877
Snacks
Segment Reporting Information [Line Items]
Net sales	1,656	1,522	3,303	3,076
Cereal
Segment Reporting Information [Line Items]
Net sales	1,336	1,444	2,710	2,769
Frozen
Segment Reporting Information [Line Items]
Net sales	267	284	564	578
Noodles and other
Segment Reporting Information [Line Items]
Net sales	$ 296	$ 215	$ 562	$ 454