Document and Entity Information	9 Months Ended
	Sep. 30, 2018 shares
Document and Entity Information [Abstract]
Entity Registrant Name	WEST PHARMACEUTICAL SERVICES INC
Entity Central Index Key	0000105770
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding	74,079,671
Entity Current Reporting Status	Yes