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Goodwill and Other Intangible Assets, Net - Schedule Changes in Goodwill (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2019	Dec. 29, 2018	Dec. 30, 2017
Goodwill [Roll Forward]
Beginning Balance				$ 750	$ 750	$ 760
Foreign currency translation					(9)	(13)
Goodwill additions					1,353	3
Goodwill impairment	$ 1	$ (939)	$ 0	0	(938)	0	$ 0
Divestitures and related adjustments					(2)
Ending Balance	1,154				1,154	750	760
Accumulated impairment at December 31, 2019	(938)				(938)	0
North America
Goodwill [Roll Forward]
Beginning Balance				529	529	528
Foreign currency translation					0	(1)
Goodwill additions					1,280	2
Goodwill impairment					(653)
Divestitures and related adjustments					(2)
Ending Balance	1,154				1,154	529	528
Accumulated impairment at December 31, 2019	(653)				(653)	0
Europe
Goodwill [Roll Forward]
Beginning Balance				172	172	182
Foreign currency translation					(8)	(11)
Goodwill additions					57	1
Goodwill impairment					(221)
Divestitures and related adjustments					0
Ending Balance	0				0	172	182
Accumulated impairment at December 31, 2019	(221)				(221)	0
APAC & Emerging Markets
Goodwill [Roll Forward]
Beginning Balance				$ 49	49	50
Foreign currency translation					(1)	(1)
Goodwill additions					16	0
Goodwill impairment					(64)
Divestitures and related adjustments					0
Ending Balance	0				0	49	$ 50
Accumulated impairment at December 31, 2019	(64)				(64)	0
Vets First Choice
Goodwill [Roll Forward]
Goodwill impairment					(938)	$ 0
Goodwill adjustment	$ (4)				$ (34)