Equity Changes in Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Equity [Abstract]
Net income	$ 1,344	$ 1,254	$ 700
Foreign currency translation adjustment before tax	5	(34)	(230)
Foreign currency translation adjustments tax (expense) benefit	(53)	113	(24)
Foreign currency translation adjustments after tax	(48)	79	(254)
Unrealized gain (loss) on cash flow hedges, pre-tax	3	0	(55)
Unrealized gain (loss) on cash flow hedges, tax (expense) benefit	(1)	0	22
Unrealized gain (loss) on cash flow hedges, after-tax	2	0	(33)
Reclassifications to net income, pre-tax	8	9	11
Reclassifications to net income, tax (expense) benefit	(2)	(3)	(6)
Reclassification to net income, after-tax	6	6	5
Net experience gain (loss)	(8)	44	25
Net experience gain (loss), tax (expense) benefit	1	(12)	(9)
Net experience gain (loss), after tax	(7)	32	16
Prior service credit (cost)	1	0	(4)
Prior service credit (cost), tax (expense) benefit	0	0	2
Prior service credit (cost), after-tax	1	0	(2)
Net experience loss, pre-tax	(5)	0	3
Net experience loss, tax (expense) benefit	1	0	(1)
Net experience loss, after-tax	(4)	0	2
Prior service cost	0	1	5
Prior service cost, tax (expense) benefit	0	0	(1)
Prior service cost, after-tax	0	1	4
Venezuela deconsolidation loss, pre-tax	0	0	63
Venezuela deconsolidation loss, tax (expense) benefit	0	0	0
Venezuela deconsolidation loss related to CTA, net of tax	0	0	63
Other Comprehensive Income (Loss), before Tax	4	20	(182)
Other Comprehensive Income (Loss), Tax	(54)	98	(17)
Other Comprehensive Income (loss)	(50)	118	(199)
Comprehensive income	1,294	1,372	501
Net income (loss) attributable to noncontrolling interests	8	0	1
Other comprehensive income (loss) attributable to noncontrolling interests	(7)	0	0
Comprehensive income attributable to Kellogg Company	$ 1,293	$ 1,372	$ 500