Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

Name:	us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue	$ 731.1	$ 736.2	$ 3,066.8	$ 2,889.0	$ 2,913.5
Companion Animal Disease Prevention
Disaggregation of Revenue [Line Items]
Revenue	185.9	201.3	804.6	660.2	628.4
Companion Animal Therapeutics
Disaggregation of Revenue [Line Items]
Revenue	81.4	62.3	283.1	260.8	255.6
Food Animal Future Protein & Health
Disaggregation of Revenue [Line Items]
Revenue	167.2	166.7	711.2	649.2	630.8
Food Animal Ruminants & Swine
Disaggregation of Revenue [Line Items]
Revenue	274.1	282.5	1,174.0	1,175.0	1,309.2
Strategic Exits(1)
Disaggregation of Revenue [Line Items]
Revenue	$ 22.5	$ 23.4	$ 93.9	$ 143.8	$ 89.5