Reportable Segments Supplemental Product Information (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 27, 2020	Mar. 28, 2020	Jun. 29, 2019	Jun. 27, 2020		Jun. 29, 2019
Segment Reporting Information [Line Items]
Net sales	$ 3,465		$ 3,461	$ 6,877		$ 6,983
Snacks
Segment Reporting Information [Line Items]
Net sales	1,522		1,741	3,076	[1]	3,521
Snacks | Revision of prior period, reclassification, adjustment
Segment Reporting Information [Line Items]
Net sales		$ 229
Cereal
Segment Reporting Information [Line Items]
Net sales	1,444		1,256	2,769	[1]	2,531
Cereal | Revision of prior period, reclassification, adjustment
Segment Reporting Information [Line Items]
Net sales		$ (229)
Frozen
Segment Reporting Information [Line Items]
Net sales	284		256	578		527
Noodles and other
Segment Reporting Information [Line Items]
Net sales	$ 215		$ 208	$ 454		$ 404

[1] The year-to-date snacks and cereal net sales reflect the correction of an error in the Company’s first quarter 2020 disclosure. First quarter net sales for snacks was understated $229 million and net sales for cereal was overstated $229 million within the disclosure included in our previously issued first quarter financial statements. The revisions, which did not impact consolidated net sales, are not considered material to the first or second quarter 2020 financial statements.