Revenue - Revenue by Species (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue from External Customer [Line Items]
Revenue	$ 1,548	$ 1,547	$ 3,082	$ 3,002
Contract Manufacturing and Human Health Diagnostics [Member]
Revenue from External Customer [Line Items]
Revenue	17	25	37	44
Cattle
Revenue from External Customer [Line Items]
Revenue	320	379	690	759
Swine
Revenue from External Customer [Line Items]
Revenue	146	158	303	307
Poultry
Revenue from External Customer [Line Items]
Revenue	135	143	283	282
Fish
Revenue from External Customer [Line Items]
Revenue	30	25	56	48
Sheep and other
Revenue from External Customer [Line Items]
Revenue	18	19	34	35
Companion animal
Revenue from External Customer [Line Items]
Revenue	649	724	1,366	1,431
Dogs and Cats [Member]
Revenue from External Customer [Line Items]
Revenue	831	754	1,577	1,442
Livestock
Revenue from External Customer [Line Items]
Revenue	882	798	1,679	1,527
Other pharmaceuticals
Revenue from External Customer [Line Items]
Revenue	192	187	389	377
Horses
Revenue from External Customer [Line Items]
Revenue	$ 51	$ 44	$ 102	$ 85