Accounting Policies Impacts of Adoption of Standards Related to Revenue Recognition, Leases and Cash Flow to Previously Reported Results (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017	Dec. 30, 2017
Consolidated Balance Sheet
Other assets	$ 1,112		$ 1,112		$ 1,027
Other current liabilities	1,329		1,329		1,474
Deferred income taxes	714		714		355
Retained earnings	7,743		7,743		7,069
Consolidated Statement of Income
Net sales	3,360	$ 3,175	6,761	$ 6,423
Cost of goods sold	2,151	1,950	4,300	4,038
Selling, general and administrative expense	735	840	1,477	1,720
Other income (expense), net	69	63	139	151
Income taxes	70	102	137	145
Net income attributable to Kellogg Company	$ 596	$ 283	$ 1,040	$ 549
Per share amounts:
Basic earnings (in dollars per share)	$ 1.72	$ 0.81	$ 3.00	$ 1.57
Diluted earnings (in dollars per share)	$ 1.71	$ 0.80	$ 2.99	$ 1.56
Consolidated Statement of Cash Flows
Net income	$ 599	$ 283	$ 1,043	$ 549	1,254
Deferred income taxes			69	(66)
Trade receivables			(83)	(716)
Other			(67)	36
All other current assets and liabilities			(245)	4
Net cash provided by (used in) operating activities			447	92
Collections of deferred purchase price on securitized trade receivables			0	568
Investment in unconsolidated entities, net proceeds				0
Net cash provided by (used in) investing activities			$ (661)	300
As previously reported
Consolidated Balance Sheet
Other assets					1,026
Other current liabilities					1,431
Deferred income taxes					363
Retained earnings					7,103
Consolidated Statement of Income
Net sales		3,187		6,441
Cost of goods sold		1,922		3,972
Selling, general and administrative expense		812		1,656
Other income (expense), net		(6)		(3)
Income taxes		102		144
Net income attributable to Kellogg Company		$ 282		$ 544
Per share amounts:
Basic earnings (in dollars per share)		$ 0.81		$ 1.56
Diluted earnings (in dollars per share)		$ 0.80		$ 1.54
Consolidated Statement of Cash Flows
Net income				$ 544
Deferred income taxes				(67)
Trade receivables				(148)
Other				30
All other current assets and liabilities				10
Net cash provided by (used in) operating activities				654
Collections of deferred purchase price on securitized trade receivables				0
Investment in unconsolidated entities, net proceeds				6
Net cash provided by (used in) investing activities				(262)
Revenue recognition ASU
Consolidated Balance Sheet
Other assets					1
Other current liabilities					43
Deferred income taxes					(8)
Retained earnings					$ (34)
Consolidated Statement of Income
Net sales		$ (12)		(18)
Cost of goods sold		(17)		(33)
Selling, general and administrative expense		4		9
Other income (expense), net		0		0
Income taxes		0		1
Net income attributable to Kellogg Company		$ 1		$ 5
Per share amounts:
Basic earnings (in dollars per share)		$ 0.00		$ 0.01
Diluted earnings (in dollars per share)		$ 0.00		$ 0.02
Consolidated Statement of Cash Flows
Net income				$ 5
Deferred income taxes				1
Trade receivables				0
Other				0
All other current assets and liabilities				(6)
Net cash provided by (used in) operating activities				0
Collections of deferred purchase price on securitized trade receivables				0
Investment in unconsolidated entities, net proceeds				0
Net cash provided by (used in) investing activities				0
Pension ASU
Consolidated Statement of Income
Net sales		$ 0		0
Cost of goods sold		45		99
Selling, general and administrative expense		24		55
Other income (expense), net		69		154
Income taxes		0		0
Net income attributable to Kellogg Company		$ 0		$ 0
Per share amounts:
Basic earnings (in dollars per share)		$ 0.00		$ 0.00
Diluted earnings (in dollars per share)		$ 0.00		$ 0.00
Cash Flow ASU
Consolidated Statement of Cash Flows
Net income				$ 0
Deferred income taxes				0
Trade receivables				(568)
Other				6
All other current assets and liabilities				0
Net cash provided by (used in) operating activities				(562)
Collections of deferred purchase price on securitized trade receivables				568
Investment in unconsolidated entities, net proceeds				(6)
Net cash provided by (used in) investing activities				$ 562