Reportable Segments Supplemental Product Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Net sales	$ 3,461	$ 3,360	$ 6,983	$ 6,761
Snacks
Segment Reporting Information [Line Items]
Net sales	1,741	1,684	3,521	3,458
Cereal
Segment Reporting Information [Line Items]
Net sales	1,256	1,304	2,531	2,655
Frozen
Segment Reporting Information [Line Items]
Net sales	256	247	527	523
Noodles and other
Segment Reporting Information [Line Items]
Net sales	$ 208	$ 125	$ 404	$ 125