Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Apr. 03, 2021	Mar. 28, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 371	$ 350
Other comprehensive income (loss), pre-tax:
Foreign currency translation adjustments, pre-tax	33	(241)
Cash flow hedges, pre-tax:
Unrealized gain (loss) on cash flow hedges, pre-tax	78	(65)
Reclassification to net income, pre-tax	5	2
Postretirement and postemployment benefits reclassification to net income, pre-tax:
Net experience (gain) loss	(1)	(1)
Available-for-sale securities, pre-tax
Unrealized gain (loss) on available-for-sale securities, pre-tax	(2)	(3)
Other comprehensive income (loss), pre-tax	113	(308)
Other comprehensive income (loss), tax (expense) benefit
Foreign currency translation adjustments, tax (expense) benefit	(34)	(20)
Cash flow hedges, tax (expense) benefit:
Unrealized gain (loss) on cash flow hedges, tax (expense) benefit	(21)	17
Reclassification to net income, tax (expense) benefit	(1)	0
Postretirement and postemployment benefits reclassification to net income, tax (expense) benefit:
Net experience loss, 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
Other comprehensive income (loss), tax (expense) benefit	(56)	(3)
Other comprehensive income (loss), after tax:
Foreign currency translation adjustments, after-tax	(1)	(261)
Cash flow hedges, after tax
Unrealized gain (loss) on cash flow hedges, after-tax	57	(48)
Reclassification to net income, after-tax	4	2
Postretirement and postemployment benefits reclassification to net income, after-tax:
Net experience (gain) loss, after-tax	(1)	(1)
Available-for-sale securities, after tax
Unrealized gain (loss) on available-for-sale securities, after-tax	(2)	(3)
Other comprehensive income (loss)	57	(311)
Comprehensive income	428	39
Net income attributable to noncontrolling interests	3	3
Other comprehensive income (loss) attributable to noncontrolling interests	(10)	(32)
Comprehensive income attributable to Kellogg Company	$ 435	$ 68