Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 03, 2021	Jun. 27, 2020	Jul. 03, 2021	Jun. 27, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 385	$ 354	$ 756	$ 704
Other comprehensive income (loss), pre-tax:
Foreign currency translation adjustments, pre-tax	8	(20)	41	(261)
Cash flow hedges, pre-tax:
Unrealized gain (loss) on cash flow hedges, pre-tax	(39)	12	39	(53)
Reclassification to net income, pre-tax	10	5	15	7
Postretirement and postemployment benefits reclassification to net income, pre-tax:
Net experience (gain) loss	(1)	(1)	(2)	(2)
Prior service cost		(1)		(1)
Available-for-sale securities, pre-tax
Unrealized gain (loss) on available-for-sale securities, pre-tax	1	5	(1)	2
Other comprehensive income (loss), pre-tax	(21)	0	92	(308)
Other comprehensive income (loss), tax (expense) benefit
Foreign currency translation adjustments, tax (expense) benefit	11	10	(23)	(10)
Cash flow hedges, tax (expense) benefit:
Unrealized gain (loss) on cash flow hedges, tax (expense) benefit	11	(3)	(10)	14
Reclassification to net income, tax (expense) benefit	(3)	(2)	(4)	(2)
Postretirement and postemployment benefits reclassification to net income, tax (expense) benefit:
Net experience loss, tax (expense) benefit	1	1	1	1
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	0	0
Other comprehensive income (loss), tax (expense) benefit	20	6	(36)	3
Other comprehensive income (loss), after tax:
Foreign currency translation adjustments, after-tax	19	(10)	18	(271)
Cash flow hedges, after tax
Unrealized gain (loss) on cash flow hedges, after-tax	(28)	9	29	(39)
Reclassification to net income, after-tax	7	3	11	5
Postretirement and postemployment benefits reclassification to net income, after-tax:
Net experience (gain) loss, after-tax	0	0	(1)	(1)
Prior service cost, after-tax		(1)		(1)
Available-for-sale securities, after tax
Unrealized gain (loss) on available-for-sale securities, after-tax	1	5	(1)	2
Other comprehensive income (loss)	(1)	6	56	(305)
Comprehensive income	384	360	812	399
Net income attributable to noncontrolling interests	5	3	8	6
Other comprehensive income (loss) attributable to noncontrolling interests	(3)	(4)	(13)	(36)
Comprehensive income attributable to Kellogg Company	$ 382	$ 361	$ 817	$ 429