Revenue - Revenue by Product (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
Vaccines
Revenue from External Customer [Line Items]
Revenue	336	370	685	728
Other pharmaceuticals
Revenue from External Customer [Line Items]
Revenue	192	187	389	377
Anti-infectives
Revenue from External Customer [Line Items]
Revenue	241	293	521	579
Parasiticides
Revenue from External Customer [Line Items]
Revenue	307	266	562	497
Medicated feed additives
Revenue from External Customer [Line Items]
Revenue	109	115	234	227
Animal health diagnostics
Revenue from External Customer [Line Items]
Revenue	69	65	129	125
Other non-pharmaceuticals
Revenue from External Customer [Line Items]
Revenue	50	41	101	81
Total products and services
Revenue from External Customer [Line Items]
Revenue	1,531	1,522	3,045	2,958
Dermatology
Revenue from External Customer [Line Items]
Revenue	227	185	424	344
Cattle
Revenue from External Customer [Line Items]
Revenue	$ 320	$ 379	$ 690	$ 759