Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 285	$ 444
Other comprehensive income (loss), pre-tax:
Foreign currency translation adjustments, pre-tax	66	30
Cash flow hedges, pre-tax:
Reclassification to net income, pre-tax	1	2
Postretirement and postemployment benefits reclassification to net income, pre-tax:
Net experience (gain) loss	(1)	(1)
Unrealized gain (loss) on available-for-sale securities, pre-tax	2
Other comprehensive income (loss), pre-tax	68	31
Other comprehensive income (loss), tax (expense) benefit
Foreign currency translation adjustments, tax (expense) benefit	(10)	19
Cash flow hedges, tax (expense) benefit:
Reclassification to net income, tax (expense) benefit	0	0
Postretirement and postemployment benefits reclassification to net income, tax (expense) benefit:
Net experience loss, tax (expense) benefit	0	0
Unrealized gain (loss) on available-for-sale securities, tax (expense) benefit	0
Other comprehensive income (loss), tax (expense) benefit	(10)	19
Other comprehensive income (loss), after tax:
Foreign currency translation adjustments, after-tax	56	49
Cash flow hedges, after tax
Reclassification to net income, after-tax	1	2
Postretirement and postemployment benefits reclassification to net income, after-tax:
Net experience (gain) loss, after-tax	(1)	(1)
Unrealized gain (loss) on available-for-sale securities, after-tax	2
Other comprehensive income (loss)	58	50
Comprehensive income	343	494
Net income (loss) attributable to noncontrolling interests	3	0
Other comprehensive income (loss) attributable to noncontrolling interests	3	0
Comprehensive income attributable to Kellogg Company	$ 337	$ 494