Reportable Segments Supplemental Product Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Net sales	$ 3,522	$ 3,401
Snacks
Segment Reporting Information [Line Items]
Net sales	1,780	1,775
Cereal
Segment Reporting Information [Line Items]
Net sales	1,275	1,351
Frozen
Segment Reporting Information [Line Items]
Net sales	271	275
Noodles and other
Segment Reporting Information [Line Items]
Net sales	$ 196	$ 0