Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 248	$ 383	$ 825	$ 1,426
Other comprehensive income (loss), pre-tax:
Foreign currency translation adjustments, pre-tax	35	(5)	96	(29)
Cash flow hedges, pre-tax:
Unrealized gain (loss) on cash flow hedges, pre-tax	(12)	0	(12)	3
Reclassification to net income, pre-tax	(1)	2	2	6
Postretirement and postemployment benefits reclassification to net income, pre-tax:
Net experience (gain) loss	(1)	(1)	(3)	(3)
Prior service cost		(1)		(1)
Available-for-sale securities, pre-tax
Unrealized gain (loss) on available-for-sale securities, pre-tax	1		4
Reclassification to net income on available-for-sale securities, pre-tax	(4)		(4)
Other comprehensive income (loss), pre-tax	18	(5)	83	(24)
Other comprehensive income (loss), tax (expense) benefit
Foreign currency translation adjustments, tax (expense) benefit	(38)	(7)	(47)	(34)
Cash flow hedges, tax (expense) benefit:
Unrealized gain (loss) on cash flow hedges, tax (expense) benefit	4	0	4	(1)
Reclassification to net income, tax (expense) benefit	0	(1)	(1)	(2)
Postretirement and postemployment benefits reclassification to net income, tax (expense) benefit:
Net experience loss, tax (expense) benefit	0	0	1	0
Prior service cost, tax (expense) benefit		0		0
Available-for-sale securities, tax (expense) benefit
Unrealized gain (loss) on available-for-sale securities, tax (expense) benefit	0		0
Reclassification to net income on available for sale of securities, tax (expense) benefit	0		0
Other comprehensive income (loss), tax (expense) benefit	(34)	(8)	(43)	(37)
Other comprehensive income (loss), after tax:
Foreign currency translation adjustments, after-tax	(3)	(12)	49	(63)
Cash flow hedges, after tax
Unrealized gain (loss) on cash flow hedges, after-tax	(8)	0	(8)	2
Reclassification to net income, after-tax	(1)	1	1	4
Postretirement and postemployment benefits reclassification to net income, after-tax:
Net experience (gain) loss, after-tax	(1)	(1)	(2)	(3)
Prior service cost, after-tax		(1)		(1)
Available-for-sale securities, after tax
Unrealized gain (loss) on available-for-sale securities, after-tax	1		4
Reclassification to net income on available for sale securities, after tax	(4)		(4)
Other comprehensive income (loss)	(16)	(13)	40	(61)
Comprehensive income	232	370	865	1,365
Net income attributable to noncontrolling interests	1	3	10	6
Other comprehensive income (loss) attributable to noncontrolling interests	(2)	(2)	1	(6)
Comprehensive income attributable to Kellogg Company	$ 233	$ 369	$ 854	$ 1,365