Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 599	$ 283	$ 1,043	$ 549
Other comprehensive income (loss), pre-tax:
Foreign currency translation adjustments, pre-tax	(54)	(66)	(24)	10
Cash flow hedges, pre-tax:
Unrealized gain (loss) on cash flow hedges, pre-tax	3		3
Reclassification to net income, pre-tax	2	2	4	4
Postretirement and postemployment benefits reclassification to net income, pre-tax:
Net experience loss	(1)	0	(2)	1
Other comprehensive income (loss), pre-tax	(50)	(64)	(19)	15
Other comprehensive income (loss), tax (expense) benefit
Foreign currency translation adjustments, tax (expense) benefit	(46)	57	(27)	66
Cash flow hedges, tax (expense) benefit:
Unrealized gain (loss) on cash flow hedges, tax (expense) benefit	(1)		(1)
Reclassification to net income, tax (expense) benefit	(1)	0	(1)	(1)
Postretirement and postemployment benefits reclassification to net income, tax (expense) benefit:
Net experience loss, tax (expense) benefit	0	0	0	0
Other comprehensive income (loss), tax (expense) benefit	(48)	57	(29)	65
Other comprehensive income (loss), after tax:
Foreign currency translation adjustments, after-tax	(100)	(9)	(51)	76
Cash flow hedges, after tax
Unrealized gain (loss) on cash flow hedges, after-tax	2		2
Reclassification to net income, after-tax	1	2	3	3
Postretirement and postemployment benefits reclassification to net income, after-tax:
Net experience loss, after-tax	(1)	0	(2)	1
Other comprehensive income (loss)	(98)	(7)	(48)	80
Comprehensive income	501	276	995	629
Net income (loss) attributable to noncontrolling interests	3	$ 0	3	$ 0
Other comprehensive income (loss) attributable to noncontrolling interests	(4)		(4)
Comprehensive income attributable to Kellogg Company	$ 502		$ 996