Segment and Other Revenue Information - Revenue by Major Product Category (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 02, 2017	Jul. 03, 2016	Jul. 02, 2017	Jul. 03, 2016
Revenue from External Customer [Line Items]
Revenue	$ 1,269	$ 1,208	$ 2,500	$ 2,370
Anti-infectives
Revenue from External Customer [Line Items]
Revenue	278	272	546	563
Vaccines
Revenue from External Customer [Line Items]
Revenue	324	310	643	611
Parasiticides
Revenue from External Customer [Line Items]
Revenue	206	189	390	334
Medicated feed additives
Revenue from External Customer [Line Items]
Revenue	121	128	244	266
Other pharmaceuticals
Revenue from External Customer [Line Items]
Revenue	282	248	554	469
Other non-pharmaceuticals
Revenue from External Customer [Line Items]
Revenue	46	49	100	102
Contract manufacturing
Revenue from External Customer [Line Items]
Revenue	$ 12	$ 12	$ 23	$ 25