Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 292	$ 599	$ 577	$ 1,043
Other comprehensive income (loss), pre-tax:
Foreign currency translation adjustments, pre-tax	(5)	(54)	61	(24)
Cash flow hedges, pre-tax:
Unrealized gain (loss) on cash flow hedges, pre-tax		3		3
Reclassification to net income, pre-tax	2	2	3	4
Postretirement and postemployment benefits reclassification to net income, pre-tax:
Net experience (gain) loss	(1)	(1)	(2)	(2)
Unrealized gain (loss) on available-for-sale securities, pre-tax	1		3
Other comprehensive income (loss), pre-tax	(3)	(50)	65	(19)
Other comprehensive income (loss), tax (expense) benefit
Foreign currency translation adjustments, tax (expense) benefit	1	(46)	(9)	(27)
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)	(1)	(1)	(1)
Postretirement and postemployment benefits reclassification to net income, tax (expense) benefit:
Net experience loss, tax (expense) benefit	1	0	1	0
Unrealized gain (loss) on available-for-sale securities, tax (expense) benefit	0		0
Other comprehensive income (loss), tax (expense) benefit	1	(48)	(9)	(29)
Other comprehensive income (loss), after tax:
Foreign currency translation adjustments, after-tax	(4)	(100)	52	(51)
Cash flow hedges, after tax
Unrealized gain (loss) on cash flow hedges, after-tax		2		2
Reclassification to net income, after-tax	1	1	2	3
Postretirement and postemployment benefits reclassification to net income, after-tax:
Net experience (gain) loss, after-tax	0	(1)	(1)	(2)
Unrealized gain (loss) on available-for-sale securities, after-tax	1		3
Other comprehensive income (loss)	(2)	(98)	56	(48)
Comprehensive income	290	501	633	995
Net income attributable to noncontrolling interests	6	3	9	3
Other comprehensive income (loss) attributable to noncontrolling interests	0	(4)	3	(4)
Comprehensive income attributable to Kellogg Company	$ 284	$ 502	$ 621	$ 996