Revenue - Revenue by Species (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue from External Customer [Line Items]
Revenue	$ 1,786	$ 1,584	$ 4,868	$ 4,586
Contract Manufacturing and Human Health Diagnostics [Member]
Revenue from External Customer [Line Items]
Revenue	23	19	60	63
Cattle
Revenue from External Customer [Line Items]
Revenue	417	389	1,107	1,148
Swine
Revenue from External Customer [Line Items]
Revenue	151	142	454	449
Poultry
Revenue from External Customer [Line Items]
Revenue	129	135	412	417
Fish
Revenue from External Customer [Line Items]
Revenue	45	42	101	90
Sheep and other
Revenue from External Customer [Line Items]
Revenue	26	23	60	58
Companion animal
Revenue from External Customer [Line Items]
Revenue	768	731	2,134	2,162
Dogs and Cats [Member]
Revenue from External Customer [Line Items]
Revenue	947	789	2,524	2,231
Livestock
Revenue from External Customer [Line Items]
Revenue	995	834	2,674	2,361
Other pharmaceuticals
Revenue from External Customer [Line Items]
Revenue	208	196	597	573
Horses
Revenue from External Customer [Line Items]
Revenue	$ 48	$ 45	$ 150	$ 130