Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Jan. 31, 2020	Jun. 30, 2019
Document and Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	1-8036
Entity Registrant Name	WEST PHARMACEUTICAL SERVICES, INC.
Entity Incorporation, State or Country Code	PA
Entity Tax Identification Number	23-1210010
Entity Address, Address Line One	530 Herman O. West Drive
Entity Address, City or Town	Exton
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19341-0645
City Area Code	610
Local Phone Number	594-2900
Title of 12(b) Security	Common Stock, par value $.25 per share
Trading Symbol	WST
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 9,218,126,218
Entity Common Stock, Shares Outstanding		73,837,449
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2019
Entity Central Index Key	0000105770