Reportable Segments Supplemental Product Information (Details) - USD ($) $ in Millions	3 Months Ended
	Apr. 03, 2021	Mar. 28, 2020
Segment Reporting Information [Line Items]
Net sales	$ 3,584	$ 3,412
Snacks
Segment Reporting Information [Line Items]
Net sales	1,647	1,554
Cereal
Segment Reporting Information [Line Items]
Net sales	1,374	1,325
Frozen
Segment Reporting Information [Line Items]
Net sales	297	294
Noodles and other
Segment Reporting Information [Line Items]
Net sales	$ 266	$ 239