Revenue - Revenue by Species (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from External Customer [Line Items]
Revenues	$ 1,674	$ 1,584	$ 1,547	$ 1,455	$ 1,564	$ 1,480	$ 1,415	$ 1,366	$ 6,260	$ 5,825	$ 5,307
Cattle
Revenue from External Customer [Line Items]
Revenues									1,654	1,754	1,735
Swine
Revenue from External Customer [Line Items]
Revenues									611	663	621
Poultry
Revenue from External Customer [Line Items]
Revenues									559	522	479
Fish
Revenue from External Customer [Line Items]
Revenues									134	132	118
Other
Revenue from External Customer [Line Items]
Revenues									72	83	84
Livestock
Revenue from External Customer [Line Items]
Revenues									3,030	3,154	3,037
Dogs and Cats
Revenue from External Customer [Line Items]
Revenues									195	168	151
Horses
Revenue from External Customer [Line Items]
Revenues									2,950	2,445	2,075
Companion Animal
Revenue from External Customer [Line Items]
Revenues									3,145	2,613	2,226
Contract Manufacturing and Human Health Diagnostics [Member]
Revenue from External Customer [Line Items]
Revenues									$ 85	$ 58	$ 44