Comprehensive Income Statement - USD ($) $ in Millions	12 Months Ended
	Jan. 02, 2021	Dec. 28, 2019	Dec. 29, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 1,264	$ 977	$ 1,344
Other comprehensive income (loss), pre-tax:
Foreign currency translation adjustment before tax	(405)	100	5
Cash flow hedges, pre-tax:
Unrealized gain (loss) on cash flow hedges, pre-tax	(9)	5	3
Reclassifications to net income, pre-tax	14	4	8
Postretirement and postemployment benefit amounts arising during the period, pre-tax:
Net experience gain (loss)	(4)	(16)	(8)
Prior service credit (cost)	(21)	3	1
Postretirement and postemployment benefits reclassification to net income, pre-tax:
Net experience (gain) loss, pre-tax	(3)	(5)	(5)
Prior service (credit) cost, pre-tax	(1)	(1)	0
Available-for-sale securities, pre-tax
Unrealized gain (loss) on available-for-sale securities, pre-tax	3	4	0
Reclassification to net income on available-for-sale securities, pre-tax	0	(4)	0
Other comprehensive income (loss), pre-tax	(426)	90	4
Other comprehensive income (loss), tax (expense) benefit:
Foreign currency translation adjustments tax (expense) benefit	84	(19)	(53)
Cash flow hedges, tax (expense) benefit:
Unrealized gain (loss) on cash flow hedges, tax (expense) benefit	2	(1)	(1)
Reclassifications to net income, tax (expense) benefit	(4)	(1)	(2)
Postretirement and postemployment benefit amounts arising during the period, tax (expense) benefit:
Net experience gain (loss), tax (expense) benefit	1	5	1
Prior service credit (cost), tax (expense) benefit	6	(1)	0
Postretirement and postemployment benefits reclassification to net income, tax (expense) benefit:
Net experience (gain) loss, tax (expense) benefit	1	1	1
Prior service (credit) cost, tax (expense) benefit	0	0	0
Available-for-sale securities, tax (expense) benefit
Unrealized gain (loss) on available-for-sale securities, tax (expense) benefit	0	0	0
Reclassification to net income on available-for-sale securities, tax (expense) benefit	0	0	0
Other comprehensive income (loss), tax (expense) benefit	90	(16)	(54)
Other comprehensive income (loss), after-tax
Foreign currency translation adjustments after tax	(321)	81	(48)
Cash flow hedges, after-tax:
Unrealized gain (loss) on cash flow hedges, after-tax	(7)	4	2
Reclassification to net income, after-tax	10	3	6
Postretirement and postemployment benefit amounts arising during the period, after-tax
Net experience gain (loss), after tax	(3)	(11)	(7)
Prior service credit (cost), after-tax	(15)	2	1
Postretirement and postemployment benefits reclassification to net income, after-tax
Net experience loss, after-tax	(2)	(4)	(4)
Prior service cost, after-tax	(1)	(1)	0
Available-for-sale securities, after-tax
Unrealized gain (loss) on available-for-sale securities, after-tax	3	4	0
Reclassification to net income on available-for-sale securities, after-tax	0	(4)	0
Other comprehensive income (loss)	(336)	74	(50)
Comprehensive income	928	1,051	1,294
Net income (loss) attributable to noncontrolling interests	13	17	8
Other comprehensive income (loss) attributable to noncontrolling interests	(52)	0	(7)
Comprehensive income attributable to Kellogg Company	$ 967	$ 1,034	$ 1,293