Reportable Segments Supplemental product information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 30, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net sales	$ 3,317	$ 3,469	$ 3,360	$ 3,401	$ 3,185	$ 3,246	$ 3,175	$ 3,248	$ 13,547	$ 12,854	$ 12,965
Snacks [Member]
Segment Reporting Information [Line Items]
Net sales									6,797	6,683	6,655
Retail Channel Cereal [Member]
Segment Reporting Information [Line Items]
Net sales									5,208	5,222	5,402
Frozen [Member]
Segment Reporting Information [Line Items]
Net sales									$ 1,542	$ 949	$ 908