Revenue - Revenue by Major Species (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Revenue from External Customer [Line Items]
Revenue		$ 1,455	$ 1,366
Livestock
Revenue from External Customer [Line Items]
Revenue		707	770
Livestock | U.S.
Revenue from External Customer [Line Items]
Revenue		273	292
Livestock | International
Revenue from External Customer [Line Items]
Revenue		434	478
Companion animal
Revenue from External Customer [Line Items]
Revenue		729	590
Companion animal | U.S.
Revenue from External Customer [Line Items]
Revenue		445	342
Companion animal | International
Revenue from External Customer [Line Items]
Revenue		284	248
Operating Segments | U.S.
Revenue from External Customer [Line Items]
Revenue		718	634
Operating Segments | International
Revenue from External Customer [Line Items]
Revenue	[1]	$ 718	$ 726

[1] Revenue denominated in euros was $181 million and $184 million for the three months ended March 31, 2019, and March 31, 2018, respectively.