Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 383	$ 288	$ 1,426	$ 837
Other comprehensive income (loss), pre-tax:
Foreign currency translation adjustments, pre-tax	(5)	(6)	(29)	4
Cash flow hedges, pre-tax:
Unrealized gain (loss) on cash flow hedges, pre-tax	0		3
Reclassification to net income, pre-tax	2	3	6	7
Postretirement and postemployment benefits reclassification to net income, pre-tax:
Net experience loss	(1)	0	(3)	1
Prior service cost	(1)		(1)
Other comprehensive income (loss), pre-tax	(5)	(3)	(24)	12
Other comprehensive income (loss), tax (expense) benefit
Foreign currency translation adjustments, tax (expense) benefit	(7)	33	(34)	99
Cash flow hedges, tax (expense) benefit:
Unrealized gain (loss) on cash flow hedges, tax (expense) benefit	0		(1)
Reclassification to net income, tax (expense) benefit	(1)	(1)	(2)	(2)
Postretirement and postemployment benefits reclassification to net income, tax (expense) benefit:
Net experience loss, tax (expense) benefit	0	0	0	0
Prior service cost, tax (expense) benefit	0		0
Other comprehensive income (loss), tax (expense) benefit	(8)	32	(37)	97
Other comprehensive income (loss), after tax:
Foreign currency translation adjustments, after-tax	(12)	27	(63)	103
Cash flow hedges, after tax
Unrealized gain (loss) on cash flow hedges, after-tax	0		2
Reclassification to net income, after-tax	1	2	4	5
Postretirement and postemployment benefits reclassification to net income, after-tax:
Net experience loss, after-tax	(1)	0	(3)	1
Prior service cost, after-tax	(1)		(1)
Other comprehensive income (loss)	(13)	29	(61)	109
Comprehensive income	370	317	1,365	946
Net income (loss) attributable to noncontrolling interests	3	$ 0	6	$ 0
Other comprehensive income (loss) attributable to noncontrolling interests	(2)		(6)
Comprehensive income attributable to Kellogg Company	$ 369		$ 1,365